Improved Spin-orbit Torque Induced Magnetization Switching Efficiency by Helium Ion Irradiation

Improved Spin-orbit Torque Induced Magnetization Switching Efficiency by Helium Ion Irradiation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Improved Spin-orbit Torque Induced Magnetization Switching Efficiency by Helium Ion Irradiation Suhyeok An, Eunchong Baek, Jin-A Kim, Ki-Seung Lee, Chun-Yeol You This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-997332/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Mar, 2022 Read the published version in Scientific Reports → Version 1 posted 9 You are reading this latest preprint version Abstract Increasing the efficiency of spin-orbit torque (SOT) is of great interest in spintronics devices because of its application to the non-volatile magnetic random access memory and in-logic memory devices. Accordingly, there are several studies to alter the magnetic properties and reduce the SOT switching current with Helium ion irradiation, but previous researches are focused on its quantitative changes only. Here, the authors observe the reduction of switching current and analyze the origins of Helium ion irradiation induced SOT switching current reduction. The first is from improved spin Hall angle caused by the resistivity change of heavy metal layer and second is from the reduction of surface anisotropy energy at interface between heavy metal and ferromagnet. The result shows that switching current is reduced about ~30.3% at dose of 30 ions/nm 2 and relevant parameter change is shown as improved spin Hall angle from 0.096 to 0.132 and reduced anisotropy field from 13.7 to 8.5 kOe. Altogether, the power consumption ratio is calculated based on the derived parameter and result shows that requiring power reaches only 56.0% at 30 ions/nm 2 . This analysis suggests that more efficient SOT device engineering is possible by Helium ion irradiation. Scientific Communication Materials Chemistry Materials Engineering spin-orbit torque (SOT) magnetization switching efficiency Helium ion irradiation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Spin-orbit torque (SOT) induced magnetization switching is a perspective phenomenon to magnetic material based devices because of its potential application to the non-volatile magnetic random access memory (MRAM) and in-logic memory devices. SOT devices have two main benefits compare to the spin transfer torque (STT) MRAM. First, SOT switching is much faster (~ 1 ns) than STT-MRAM (~ 10 ns). Second, SOT-MRAM have reading path separated from the writing path, it is expected that more stable devices are possible and more margins in the reading and writing currents. In SOT switching, there are two essential ingredients: structural inversion symmetry breaking and strong spin-orbit coupling (SOC). A heavy metal (HM) / ferromagnetic metal (FM) bilayer structure satisfies those requirements. When charge current passes through the HM, the spin current is created inside of HM and injected into the FM by spin Hall effect (SHE) 1 and/or the Rashba effect can create non-zero effective field at the interfaces 2 . For developing more effective SOT induced magnetization switching, many relevant parameters like spin Hall angle (SHA, θ SH ) 3 , magnetic anisotropy field 4 and Dzyaloshinskii-Moriya (DM) interaction 5 are under the investigation. Among them, θ SH , a ratio of spin current to the charge current densities, is a vital parameter as indicators of converting efficiency from electric charge to spin current densities by SHE in HM. The θ SH is one of the key players on SOT induced switching since the magnitude of SOT is proportional to the spin current. Therefore, θ SH value has been investigated heavily in various HMs, like Ta (~0.15) 6 , β-W (~0.33) 7 and Pt (~0.1) 8 , 9 . Since the discovery of SOT, intensive efforts to enhance and control the strength of SOT are conducted by annealing 10 , resistivity control of HM layer 11 , normal metal (NM) insertion 12 , 13 , alloying 14 , interface modifying 15 , 16 , and ion irradiation 17 , 18 . Among them, the method of irradiating Helium ion is known as leading a structural rearrangement while maintaining the overall atomic layer districts in the multi-stacked structure 19 even if no ions remain in the sample due to the long penetration depth (> 50 nm) 20 . Ion irradiation induced structural reorganization affects layers and interfaces, resulting in the coercivity and anisotropy field change 21 , domain wall (DW) pinning site creation 22 , modulating DM Interaction 23 , and performing magnetic skyrmions 24 . This characteristic is also evident in the case of SOT, so it has been observed in various SOT relevant effects such as reduction of switching current by SOT 18 , influence on DW dynamics 25 , and multi-level state 26 . However, none of the previous studies about Helium ion irradiation modifying SOT phenomena have been paid attention in analyzing its origins by separating the properties of HM and FM layer. Here, we successfully distinguished the effects of ion irradiations on HM/FM bilayer system, as changes of θ SH and PMA strength in HM and FM layer. We prepared Pt(5)/Co(0.8)/MgO(2) structure samples and irradiated Helium ions in various doses. After Helium ions irradiations, we measured the critical current for SOT induced switching with various in-plane field. We found that the switching current decreases from 16.1 to 11.2 mA as increasing dose amounts from 0 to 30 ions/nm 2 with the in-plane field of 3.1 kOe. For understanding the decrease of switching current, we also measured the first and second order uniaxial anisotropy fields, and θ SH determined by the harmonic Hall measurement method. By careful analysis including the second order uniaxial anisotropy field contributions, we extracted magnetization polar angular dependent effective field caused by SOT for each dose and θ SH from ΔH DL . Furthermore, we measured the effect of the dose amount on the resistivities of single Pt layers and confirmed the relation between resistivity and θ SH . Based on our analysis, the reduction of the switching current partially ascribes to the reduced anisotropy field from 13.7 to 8.5 kOe (38.0 %) and improved θ SH from 0.096 to 0.132 (27.2 %). Here, it must be mentioned that the reduction rate of switching current (30.4%) is smaller than expected reduction rate when we consider the magnetic anisotropy reduction and θ SH enhancement. Nevertheless, the calculated power consumption was 87.4%, 59.6%, and 56.0% at each dose compared with the non-irradiated sample, indicating that Helium ion irradiation can contribute to better SOT device fabrication. Results We deposited Pt(5 nm)/Co(0.8 nm)/MgO(2 nm) heterostructure sample using magnetron sputter and patterned as 10 µm width Hall bar structure by photolithography technique. In Figure 1 a, the sample structure, coordinate systems, and Helium ion irradiation area are depicted. θ M is the polar angle between magnetization direction and z-axis, θ B is the polar angle between the external magnetic field and z-axis, and ϕ is azimuthal angle from x-axis, and here we ignore the angle differences between the external magnetic field and magnetization directions in the azimuthal angle because of the negligible in-plane anisotropy. After Hall bar fabrication process, Helium ion is irradiated in vertical direction with sample plane having acceleration energy of 30 keV, beam current of 5.5 pA, and dose from 0 to 30 ions/nm 2 with step of 10 ions/nm 2 . Irradiation area covers whole Hall cross for avoiding signal mixing errors by signal differences between irradiation and non-irradiation area as shown red dotted rectangle in Figure 1 a (more explanation in Supplementary Figure S1). Measurement of SOT induced magnetization switching includes three sequences: initialization, SOT writing by pulse current, and reading from Hall resistance measurement. Firstly, sample is under strong enough +z-axis (-z-axis) direction external field to saturate the magnetization in up (down) direction as initial state. After initialized, the current pulse is injected with pulse amplitude ( Ip ) from -25 to 25 mA (25 to -25 mA) with 1 mA step. During the current pulse injection in x-axis direction in-plane magnetic field is applied to ensure deterministic switching. And the Hall resistance ( R H ) is measured in the middle of each pulse injection with 100 µA magnitude direct current (DC). Here, we should mention that the R H is unit value calculated from measured Hall voltage ( V H ) dividing with magnitude of reading current. The R H results as a function of Ip with the previous procedure shows typical hysteresis loops, as shown in Figure 1 b- 1 c, and it indicates SOT induced magnetization switching in PMA system. Here, the shown hysteresis loops in Figure 1 b are in case for dose amount of 30 ions/nm 2 . It is well known that higher in-plane field make switching more easily, but we observe that Helium ion irradiation also reduces the switching current. The SOT driven magnetization switching hysteresis loops for various doses with a fixed 2.2 kOe external in-plane field is shown in Figure 1 c. In Figure 1 d, the switching currents from magnetization switching loops at each dose and external magnetic field are depicted. In Figure 1 d, we found two features. Firstly, in small field region (0.7 kOe), rapid increase of switching current appears. We expect that this increase is caused by the nucleation of multi-domain states during SOT induced magnetization switching process (see the Supplementary Figure S2a for more details). Because of the multi-domains under small field, it is hard to compare the switching current in higher field region directly so that we will not pay attention much. The second feature is main finding of this work in larger field regions (≥1.2 kOe). We found that the switching current is reduced by increasing dose amounts. And at same dose amount, the switching current have linear relation with the external in-plane field strength under the sufficiently smaller in-plane field comparing 1st order effective anisotropy field, which is well-known behavior following \({J}_{C}=\frac{2e}{\hslash }\frac{{M}_{s}{t}_{F}}{{\theta }_{SH}}\left(\frac{{H}_{K,eff}}{2}-\frac{{H}_{x}}{\sqrt{2}}\right)\) 2 8 . And here, e is charge of electron, ℏ is Planck constant, M s is saturation magnetization, t F is thickness of FM layer, H K,eff is the 1st order anisotropy field and H x is in-plane external magnetic field parallel with current. In order to get better insight of the Helium irradiations effect, we show the switching current reduction ratio at each dose compared with the pristine sample ( \(\left|\left({I}_{P.crit}-{I}_{P,crit}^{Dose 0}\right)/{I}_{P,crit}^{Dose 0}\right|\times 100 \%\) ) as in Figure 1 e. Result shows that the switching current reduction has increasing tendency with dose amount for in-plane external field. The exceptional dependence for small field (0.7 kOe) probably ascribe to the formation of multi-domain state as seen in Supplementary Figure S2b. The reduction ratio appears largely at external field of 3.1 kOe about 14.2%, 25.5%, and 30.3% at dose of 10, 20, and 30 ions/nm 2 , respectively. Here, the possible physical origins of the switching current reduction can be the enhanced θ SH of Pt layers, and/or it can be the decrease of the effective anisotropy field of FM layer. We will discuss more details later. To understand the more details of switching behavior, the effects of Helium ion irradiation on the magnetic anisotropy fields are investigated. We conducted Anomalous Hall effect (AHE) measurement by swapping the external magnetic field in z-axis direction to obtained normalized Hall resistance ( R H (H ext )/R H (H ext =0 Oe) ) hysteresis loops, because the AHE signal is proportional to the z-component of magnetization. The normalized AHE hysteresis loops in Figure 2 a shows strong enough PMA for all samples. And each coercivity is decreasing (~ 34 %) from 271 Oe to 178 Oe as shown in Figure 2 b by increasing dose amounts. In order to obtain the 1st and 2nd order anisotropy fields ( H K,eff , H K,2 ) by using generalized Sucksmith-Thompson (GST) method (see Supplementary Figure S3), we measured normalized AHE by applying in-plane field ( H x ) along the current direction as seen in Figure 2 c. Here, it must be mentioned that the obtained 1st order anisotropy fields are the effective anisotropy including demagnetization effect, not pure anisotropy field in GST method. The H K,eff and H K,2 are shown in Figure 2 d as a function of dose. By increasing dose amount from 0 to 30 ions/nm 2 , H K,eff and H K,2 decrease 38.2%, and 27.5%, respectively. We speculate that decrease is mainly caused by interface modulation from Helium ion irradiation process, since the surface anisotropy energy is very sensitive on the quality of the interface between HM and FM layers. Although it is hard to classify and/or probe the effect of the structural modulation caused by the Helium ion irradiation, we can claim that he anisotropic field as well as the coercivity field can be reduced by the Helium ion irradiation. The magnitude of H K,2 is only less than half (40.1 %) compared with the H K,eff , however, the SOT analysis without consideration of H K,2 may lead incorrect results 29 . Not only the anisotropy characteristics, but also an important parameter in SOT induced magnetization reversal is θ SH . The harmonic Hall signal analysis is frequently used method for calculating θ SH as well as extracting SOT driven effective fields 29 , 30 . It is well known that the SOT has two contributions acting on different directions, so called field-like torque (FLT, ΔH FL ) in transverse direction and damping-like torque (DLT, ΔH DL ) effective field in longitudinal direction, consideration of AHE and PHE resistances are necessary for obtaining correct results. In Figure 3 a, the measured Hall resistance loops are shown at ϕ = 10 to 40° with fixed θ B = 80° for dose amount of 30 ions/nm 2 sample. Since the AHE and PHE contribute to the measured Hall signal as following the equation 30 , $${V}_{H}={I}_{0}{R}_{0}=\frac{{I}_{0}{R}_{AHE}}{2}\text{cos}{\theta }_{M}+\frac{{I}_{0}{R}_{PHE}}{2}{\text{sin}}^{2}{\theta }_{M}\text{sin}2\varphi$$ 1 The clear asymmetries are observed for the Hall loops in Figure 3 a in the large field. The asymmetry also increases because of the larger PHE contribution for large ϕ . And by adding and subtracting divided asymmetric Hall loop between +B to -B part and -B to +B part, one can separate the contributions of AHE and PHE as seen in Figure 3 b and Figure 3 c, respectively. Details of extracting method for AHE and PHE resistances is explained in Supplementary Figure S4. Here, Figure 3 b and Figure 3 c show the data at the angle of θ B = 80° and ϕ = 40° at each dose amount. The AHE resistance can be calculated using AHE contribution at θ B = 0°, corresponding to zero external in-plane field, and the PHE resistance can be also calculated taking linear plot on the PHE contribution from the slope of sin 2 θ M , in Equation ( 1 ). From those measurement analyses, the calculated AHE and PHE resistances are shown in Figure 3 d together. R AHE increased from 1.09 to 1.20 Ω (9.8 %) with increasing dose amounts, while R PHE varied within the range of 0.37 to 0.34 Ω. Since the ratio of R=R PHE /R AHE has an important role in analysis of the harmonic Hall measurement result, we calculated the ratio and it changes from 0.34 to 0.29 at dose of 0 and 30 ions/nm 2 , as depicted in Figure 3 e. It must be mentioned that the variation of R with Helium ion irradiation is not significant comparing to other physical quantities. One possible explanation is that the bulk magnetic properties are relatively insensitive on the Helium ion irradiation, while the surface properties, such as surface anisotropy, are more sensitive. To obtain the θ SH or SOT induced effective fields, we measure harmonic Hall with alternating current (AC) of 5.5 mA peak amplitude and 401 Hz frequency ( I AC = I 0 sin2π ft ). Because the harmonic Hall measurement is influenced by the Joule heating effect caused by current flow, we follow the four-direction method for eliminating some thermoelectric artifacts 31 . The 1st and 2nd harmonic Hall loop is measured swapping magnetic field with fixed θ B = 85° and ϕ = 0° for ΔH DL and ϕ = 90° for ΔH FL measurements. Each Hall loop result is shown in Figure 4 a- 4 c, respectively. Here, the 1st and 2nd harmonics are measured simultaneously with two lock-in amplifiers at each ϕ and dose amounts. Harmonic Hall voltage signal under AC follows the equation, $${V}_{H}={I}_{o}{R}_{H}={V}^{1\omega }\text{sin}\left(\omega t\right)-{V}^{2\omega }\text{c}\text{o}\text{s}\left(2\omega t\right)$$ 2 Although 1st voltage has almost same signal at each ϕ , 2nd voltage has completely different signals as shown Figure 4 b and Figure 4 c. These results are come from the different contribution between DLT and FLT. The 2nd order harmonic Hall voltage at each ϕ = 0° and 90° with consideration of 2nd order PMA energy follow the expression 29 , $${V}_{x}^{1\omega }={V}_{y}^{1\omega }={V}_{AHE}\text{cos}{\theta }_{M}$$ 3 $${V}_{x}^{2\omega }=\frac{{V}_{AHE}}{2} \left({A}_{1}{\Delta }{H}_{DL}-{B}_{1}{\Delta }{H}_{FL}\right)$$ 4 $${V}_{y}^{2\omega }=\frac{{V}_{AHE}\text{cos}{\theta }_{M}}{2} ({B}_{1}{\Delta }{H}_{DL}-{A}_{1}{\Delta }{H}_{FL})$$ 5 $${A}_{1}\equiv \frac{\text{s}\text{i}\text{n}{\theta }_{M}}{{H}_{K,eff}\text{cos}2{\theta }_{M}-{H}_{K,2}\text{sin}{\theta }_{M}\text{sin}3{\theta }_{M}+{H}_{ext}\text{cos}\left({\theta }_{M}-{\theta }_{H}\right)}$$ 6 $${B}_{1}\equiv \frac{R\text{s}\text{i}{\text{n}}^{2}{\theta }_{M}}{{H}_{ext}\text{sin}{\theta }_{H}}$$ 7 Following the Equation ( 2 ) to ( 7 ), we can rewrite DLT and FLT effective fields ( ΔH DL , ΔH FL ) as function of θ M from the measured harmonic Hall voltages as shown in Figure 4 d and Figure 4 e, respectively. Here, θ M can be calculated using experimentally obtained the 1st order harmonic Hall signal at each dose with Equation ( 3 ). The results show the different dose dependences on ΔH DL and ΔH FL with θ M . When the near of θ M = 15°, corresponding magnetization angle at external magnetic field of 3.1 kOe in 0 ions/nm 2 , ΔH DL has small increasing tendency as shown in the inset in Figure 4 d but ΔH FL has decreasing tendency at its magnitude according to dose amount. However, when θ M > 15°, both effective fields show great increase and complex behavior having a maximum peak point at θ M of range from 40° to 45°. According to simple macro-spin SOT model 29 , there is no magnetization direction dependence on both effective SOT fields. However, there are much experimental evidences of the magnetization direction dependence on the effective SOT fields 30 , 31 , 32 . The higher order term of SOT can be one of the possible origins of complex angular dependence. According to Ref.30, the high order term of SOT is non-negligible and may cause complex angular dependence. In addition, if Helium ion irradiation modulates the higher-order term of the SOT just similar as the higher-order term of the PMA, the change in angular dependence can be estimated as a phenomenon caused by the Helium ion irradiation. Furthermore, another possible approach explaining such magnetization direction dependent effective SOT fields is from the framework of distorted Fermi surface 33 . The θ M dependent effective fields in Figure 4 d and Figure 4 e are rather complicated angular dependence compared with the theoretical results are based on the free-electron like model Hamiltonian with exchange coupling and Rashba effect. The experimental results reflect realistic band structures so that the more complex angular dependent explanation is acceptable. It is hard to analysis the exact origins separately. However, it is also true that the varying angular dependent effective fields by degree of ion irradiation has been experimentally observed as seen in Figure 4 d and Figure 4 e. And it is worth to note that if H K,2 is not considered in the calculation, the result has quite different tendency with Figure 4 d- 4 e, suggesting the critical role of the 2nd order anisotropy in precise analysis of harmonic Hall measurement in all range of θ M (see the Supplementary Figure S5). Because θ SH is one of the most important material parameters for SOT based devices, understanding the correlation between ion irradiation induced θ SH variation and HM layer state is important. In order to reveal the effect of the Helium ion irradiation on HM layer only, we irradiated the Helium ion on single Pt layer with thickness of 5 nm as same conditions introduced in sample fabrication description. We used the 4-probe measurement technique for measuring resistance with temperature range of 5 K to 225 K and calculated resistivity using sample geometry information with measured resistance. Here, the resistivity curve and the method of calculating resistivity at 300 K are explained in Supplementary Figure S6a. The resistivity of Pt ( ρ Pt ) at 300 K and 5 K is shown in Figure 5 a and we can observe the increasing resistivity according to dose amount, 43.4 to 47.8 µΩ∙cm (109%) in 5 K and 56.8 to 60.9 µΩ∙cm (107%) in 300 K comparing 0 ions/nm 2 and 30 ions/nm 2 . Figure 5 b displays the changed ratio of temperature coefficient ( α Temp ), following ρ = ρ 0 (1 + α Temp ∙ (T-T 0 ) at linear resistivity increasing region ( T > 50 K), and residual-resistivity ratio ( RRR ), comparison of resistivities between 300 K and 5 K in here. We can find the decreasing tendency of α Temp and RRR both, it can be interpreted as increased influence of impurity at higher dose. Because the collision time is inversely proportional to the impurity density, decrease of α Temp and RRR value imply that the Helium ion irradiation makes extra scattering sources by structural distortion in Pt layer. The Figure 5 c shows the resistivity dependence of θ SH , and it can be calculated with ΔH DL at each dose value using following equation 34 , $${\theta }_{SH}=\frac{2\text{e}}{\text{\hslash }}\frac{{M}_{s}{t}_{F}{A}_{HM}}{{I}_{0}}\varDelta {H}_{DL}$$ 8 Here, A HM is the cross section area of flowing current into HM. We assume that the influence of irradiation on M s , t F , and A HM is small enough to ignore, because the irradiated dose amount is scarce to cause interlayer deformation 19 , 20 , 27 . So, we calculated the θ SH with M s = 1100 kA m - 1 , t F = 0.8 nm, A HM = 10 µm × 5 nm and ΔH DL when θ M = 15° at each dose amount using Equation ( 8 ). Error bar can be calculated as the averaged of values of the front and rear data starting from θ M = 15°. It is found that θ SH has linear relation with increased resistivity by Helium ion irradiations, as well reported 11 , 35 , 36 . The θ SH increases 0.096 to 0.132 with resistivity growth from 56.8 to 60.9 µΩ∙cm in 300 K, about 5 - 6 times greater than resistivity of bulk Pt (10.6 µΩ∙cm in 20 ℃) in literature 37 . This result suggests that Helium ion irradiation process makes extra scattering sources, and they raise the resistivity of HM layer. And the extra scattering sources cause improvement of θ SH , resulting in more effective switching of the magnetization by SOT. Although the energy efficiency in view of operating the device is slightly worse due to the ion irradiation induced resistance increasement, the improved θ SH ratio is ~ 4 times greater compared with resistivity increasement ratio. In terms of power ( P=R sample I 2 ) consumption, the change in resistance and SHA has an inverse relationship. As a result, only 87.4%, 59.6%, and 56.0% of power consumption is expected at 10, 20, and 30 ions/nm 2 , respectively. (See Figure 5 d) Here, the R sample and I are normalized resistance of HM and normalized current by θ SH at each dose. Therefore, it means that Helium ion irradiation enables more efficient data writing in terms of energy consumption. And it is worth mentioning that the critical switching current equation shown in ref.28 does not match with our actual experimental value except only linear relationship with in-plane field. We expect because the formula is based on the macro spin model as like well-known Brown paradox 38 . Furthermore, there are reports that it does not match the actual value in the micron scale sample 39 , 40 . That’s why we obtained θ SH from the spin-orbit torque effective field measurement (see Figure 5 c), not from the switching current density. Nevertheless, it is clear that the Helium ion irradiation leads to a decrease in the H K,eff , an increase in the θ SH , and the more efficient the SOT induced magnetization switching. In summary, we observe that Helium ion irradiation can properly reduce SOT induced switching current in Pt(5)/Co(0.8)/MgO(2) structure. The reduction appears 14.2%, 25.5%, and 30.3% at dose of 10, 20, and 30 ions/nm 2 comparing with the pristine sample under the in-plane external magnetic field of 3.1 kOe. For understanding of physical reasons of decreasing tendency of the switching current, we considered two main possible origins of reduction, H K,eff and θ SH . From AHE measurement and GST method, we can extract H K,eff and it decreases from 13.7 to 8.5 kOe (38.2%) comparing dose 0 and 30 ions/nm 2 . Not only H K,eff , θ SH also increase from 0.096 to 0.132 (27.2%). Furthermore, it is revealed that improvement of θ SH is consequence of increase of Pt resistivity by ion irradiation process. Although the power consumption is slightly worse due to the increase of the resistance, the decreased critical current caused by the improved θ SH has a greater impact in power consumption. As a result, the ratio of power requiring for operation of device is calculated to consume only about 56.0% for switching at 30 ions/nm 2 compared to pristine sample, and this successful analysis on Helium ion irradiation induced modulation of SOT effect can be expected to improve efficiency of SOT based spintronic devices engineering. Methods Thin film preparation and fabrication process The sample preparation process includes three steps, firstly Hall bar photolithography and deposition, secondly electrode fabrication, and Helium ion irradiation at last. This section will only explain up to step 2, and step 3 will be explained in later paragraph (See the Helium ion microscope in Methods section). The sample is fabricated with lift-off process using photolithography and magnetron sputtering system. Normal metal layer and oxide layer is deposited using DC and AC power with stack of Pt(5)/Co(0.8)/MgO(2) on single surface polished Si substrate having 300nm thickness SiO 2 oxidated surface. The patterned Hall bar geometry consists of the current line of 10 µm width and 40 µm length and voltage line of 3 µm width 16 µm length. This geometry represses the offset error caused by sample shape. After deposition and patterning of sample, we deposit the electrode with stack of Ta(5)/Cu(50) for electric measurement. Helium ion microscope HIM (Helium ion microscope, Carl Zeiss/ORION NanoFab), using high energy ionized Helium, is one of the brand-new microscopic techniques. Using HIM, we can obtain more detailed image in nano-scale structure compared with Gallium ion or electron based microscope owing to its penetration characteristic of high energy Helium ion 20 , 27 . But for utilizing HIM, we must make trimer, as the state of leaving only three atoms at the end of tip, stability and duration problems are remained. Even in such problems, the high penetration characteristic and low diffraction limitation of HIM come to be a big attraction. Because the HIM have low convergence angle, long best focus length and high penetration depth, more than few tens of nanometer scale, it also can be used as precise atomic structure destruction method. We expose the Helium ion with normal direction of sample plane with dose value of 0 to 30 ions/nm 2 at energy of 30 keV and current of 5.4 ~ 5.5 pA. The exposure process can be conducted from few hundred micron to few tens of nanometer size, and we conducted with area of 20 µm × 20 µm. The HIM is in the Central Core Research Facility center in DGIST, Korea. Transport measurement system with DC and AC current For measuring magnetic properties, we use the DC & AC source (Keithley, 6221), nano-voltmeter (Keithley, 2182A), and lock-in amplifiers (Zurich Inst. SR830). Each equipment is connected to sample using customized PCB in the 2-axis rotational holder and the direction of magnetic field is controlled by rotating holder in prefer direction using motors. For measuring SOT induced magnetization switching, we use the current source for injecting pulse and nano-voltmeter for measuring Hall voltage. The magnetization is initialized to +z direction (or -z direction) using magnetic field and switching is induced under in-plane magnetic field using sweep mode of DC & AC source. Comparing SOT induced magnetization switching measurement, the harmonic Hall measurement use different voltmeter, not nano-voltmeter but two lock-in amplifiers for detecting AC based Hall signals. One lock-in amplifier detects the 1st harmonic signal, and the other detects the 2nd signal. All lock-in amplifiers are connected to sample with same voltage line, so the 1st and 2nd harmonic signal is measured simultaneously. For temperature dependent measurement, we use the cryostat to be able to connect with nano-voltmeter and current source. The cryostat chamber also can be connected to customized PCB to instruments. The resistance is measured using 4-probe measurement with reading current of enough small current and sample atmosphere temperature can vary from 5 K to 275 K with gap of 0.25 K using chamber heater and Helium compressor system. Here, all current and voltage equipment is connected with sample using Bayonet Neill–Concelman cable for repressing noises. Declarations Acknowledgements This work is supported by the National Research Foundations of Korea (NRF-2015M3D1A1070465, NRF-2021R1A2C2007672, NRF-2020M3F3A2A02082437, NRF-2021M3F3A2A01037525, NRF-2018R1A6A3A11041061). Author contributions statement K.-S.L. and C.-Y.Y. conceived the projects; Sample fabrication was done by S.A. and J.-A.K; the measurements were performed by S.A., E.B.; Data analysis and manuscript preparation were done by S.A., K.-S.L., and C.-Y.Y.; The study was supervised by C.-Y.Y. Additional information The authors declare no competing interests. References Liu, L., Lee, O. J., Gudmundsen, T. J., Ralph, D. C. & Buhrman, R. A. Current-Induced Switching of Perpendicular Magnetized Magnetic Layers Using Spin Torque from the Spin Hall Effect. Phys. Rev. Lett , 109 , 096602 (2012). Miron, I. M. et al. Perpendicular switching of a single ferromagnetic layer induced in-plane current injection. Nature , 476 , 189–193 (2011). Emori, S., Bauer, U., Ahn, S. M., Martinez, E. & Beach, G. S. D. Current-driven dynamics of chiral ferromagnetic domain wall. Nat. Mater , 12 , 611–616 (2013). DC, M. et al. 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Hasegawa, K., Hibino, Y., Suzuki, M., Koyama, T. & Chiba, D. Enhancement of spin-orbit torque by inserting CoOx layer into Co/Pt interface. Phys. Rev. B , 98 , 020405 (2018). Yun, J. et al. Lowering critical current density for spin-orbit torque induced magnetization switching by ion irradiation. Appl. Phys. Lett , 115 , 032404 (2019). Dunne, P. et al. Helium Ion Microscopy for Reduced Spin Orbit Torque Switching Currents. Nano. Lett , 20 , 7036–7042 (2020). Fassbender, J., Ravelosona, D. & Samson, Y. J. Tailoring magnetism by light-ion irradiation. Phys. D: Appl. Phys , 37 , R179–R196 (2004). Hlawacek, G., Veligura, V., van Gastel, R. & Poelsema, B. Helium ion microscopy. J. Vac. Sci. Technol. B , 32 , 020801 (2014). Chappert, C. et al. Planar patterned magnetic media obtained by ion irradiation. SCIENCE , 280 , 1919–1922 (1998). Franken, J. H. et al. Precise control of domain wall injection and pinning using helium and gallium focused ion beams. J. Appl. Phys , 109 , 07504 (2011). Nembach, H. T. et al. Tuning of the Dzyaloshinskii-Moriya interaction by He+ ion irradiation. arXiv:2008.06762(2020). Juge, R. et al. Helium ions put magnetic skyrmions on the track. Nano Lett , 21 , 2989–2996 (2021). Zhao, X. et al. Enhancing domain wall velocity through interface intermixing in W-CoFeB-MgO films with perpendicular anisotropy. Appl. Phys. Lett , 115 , 122404 (2019). Zhao, X. et al. Spin-orbit torque driven multi-level switching in He+ irradiated W-CoFeB-MgO Hall bar with perpendicular anisotropy. Appl. Phys. Lett , 116 , 242401 (2020). Livengood, R., Tan, S., Greenzweig, Y., Notte, J. & McVey, S. Subsurface damage from helium ions as a function of dose, beam energy, and dose rate. J. Vac. Sci. Technol. B , 27 , 3244 (2009). Lee, K. S., Lee, S. W., Min, B. C. & Lee, K. -J. Threshold current for switching of a perpendicular magnetic layer induced by spin Hall effect. Appl. Phys. Lett , 102 , 112410 (2013). Yun, S. J. et al. Accurate analysis of harmonic Hall voltage measurement for spin–orbit torques. NPG Asia Materials , 9 , e449 (2017). Garello, K. et al. Symmetry and magnitude of spin–orbit torques in ferromagnetic heterostructures. Nat. Nanotechnol , 8 , 587–593 (2013). Park, E. S., Lee, D. K., Min, B. C. & Lee, K. -J. Elimination of thermoelectric artifacts in the harmonic Hall measurement of spin-orbit torque. Phys. Rev. B , 100 , 214438 (2019). Qiu, X. et al. Angular and temperature dependence of current induced spin-orbit effective fields in Ta/CoFeB/MgO nanowires. Sci. Rep , 4 , 4491 (2014). Lee, K. S. et al. Angular dependence of spin-orbit spin-transfer torques. Phys. Rev. B , 91 , 144401 (2015). Khvalkovskiy, A. V. et al. Matching domain-wall configuration and spin-orbit torques for efficient domain-wall motion. Phys. Rev. B 87, 020402(R)(2013). Sagasta, E. et al. Unveiling the mechanisms of the spin Hall effect in Ta. Phys. Rev. B , 98 , 060410 (2018). Nakagawara, K. et al. Temperature-dependent spin Hall effect tunneling spectroscopy in platinum. Appl. Phys. Lett , 115 , 162403 (2019). Serway, R. A. Principle of Physics 2nd edn (Fort Worth, Texas, USA, 1999). BrownJr. W. F. Micromagnetics (Wiley, New York, USA, 1963). Ranjbar, R., Suzuki, K. Z., Sasaki, Y., Bainsla, L. & Mizukami, S. Current-induced spin-orbit torque magnetization switching in a MnGa/Pt film with a perpendicular magnetic anisotropy. Jpn. J. Appl. Phys , 55 , 120302 (2016). Neumann, L. et al. Temperature dependence of the spin Hall angle and switching current in the nc-W(O)/CoFeB/MgO system with perpendicular magnetic anisotropy. Appl. Phys. Lett , 109 , 142405 (2016). Additional Declarations No competing interests reported. Supplementary Files SupplementaryInformation.pdf Cite Share Download PDF Status: Published Journal Publication published 02 Mar, 2022 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Major revision 22 Nov, 2021 Reviewers agreed at journal 31 Oct, 2021 Reviews received at journal 28 Oct, 2021 Reviewers agreed at journal 22 Oct, 2021 Reviewers invited by journal 22 Oct, 2021 Editor assigned by journal 22 Oct, 2021 Editor invited by journal 22 Oct, 2021 Submission checks completed at journal 22 Oct, 2021 First submitted to journal 19 Oct, 2021 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-997332","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":58432291,"identity":"13f8249c-d004-4cc6-baa4-d9750fe32743","order_by":0,"name":"Suhyeok An","email":"","orcid":"","institution":"DGIST","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Suhyeok","middleName":"","lastName":"An","suffix":""},{"id":58432292,"identity":"198f1ddb-3869-41a0-b053-96d7afc19ae7","order_by":1,"name":"Eunchong Baek","email":"","orcid":"","institution":"DGIST","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Eunchong","middleName":"","lastName":"Baek","suffix":""},{"id":58432293,"identity":"c2b69297-d05d-4370-bce6-1e91ac963436","order_by":2,"name":"Jin-A Kim","email":"","orcid":"","institution":"DGIST","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jin-A","middleName":"","lastName":"Kim","suffix":""},{"id":58432294,"identity":"97d11e6d-d3ee-4b95-89ad-a6b8cf2c9858","order_by":3,"name":"Ki-Seung Lee","email":"","orcid":"","institution":"DGIST","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ki-Seung","middleName":"","lastName":"Lee","suffix":""},{"id":58432295,"identity":"25e35292-4263-403d-92ae-3472fe4b2ef6","order_by":4,"name":"Chun-Yeol You","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzklEQVRIiWNgGAWjYNCCCmYGNijTgEgtZ0BamEnRwtgGUk6sFv4ZOYaPeedZ2/Xxnz/A8KOGwdi8gYAWiRs5xsa829KT2ySSGRh7jjGYyRwgoMVAIsdMmnfb4WQ2CaDDeBsYbCQIOQyiZQ5QC/9hBsa/xGtpOGzHxpDMwAy0xYygFokzz4oN5xxLT2CTSDY4LHNMwpigFv725I0P3tRY28v3H3z48E2NjeEMQloYBDLAMZHYACQOAG0lqAFozfEHIMqeCKWjYBSMglEwUgEA+P0z+bvkl2EAAAAASUVORK5CYII=","orcid":"","institution":"DGIST","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Chun-Yeol","middleName":"","lastName":"You","suffix":""}],"badges":[],"createdAt":"2021-10-20 01:59:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-997332/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-997332/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-022-06960-8","type":"published","date":"2022-03-02T12:19:48+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":14874601,"identity":"9a7877b5-d13a-43a6-9bb5-287e5f5f1b0c","added_by":"auto","created_at":"2021-10-25 15:44:46","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":687210,"visible":true,"origin":"","legend":"Please see the Manuscript file for the complete figure caption","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/95fb6b65635e36927da3cf31.jpg"},{"id":14874602,"identity":"27fed66b-8046-4102-a5cd-eeff8ec5b9d4","added_by":"auto","created_at":"2021-10-25 15:44:46","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":359719,"visible":true,"origin":"","legend":"AHE measurement results for Pt(5)/Co(0.8)/MgO(2 nm) samples ay various Helium ion irradiation doses amount. (a) Normalized AHE loops with the external magnetic field perpendicular (Hz) for various doses. (b) The coercivities from the AHE loops as a function of doses. (c) Normalized AHE signals of various doses with the in-plane field (Hx) for GST method. Here, the solid lines are trending lines. (d) The 1st and 2nd anisotropy fields (HK,eff, HK,2) extracted by the GST method are plotted for various doses. We measured all AHE with the reading current of 100 μA for various doses of 0, 10, 20, and 30 ions/nm2. Current flow along x-axis and Hall voltage is measured in y-axis.","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/8c28e43b1a56712046844617.jpg"},{"id":14874605,"identity":"82464efd-fd7a-4bee-a07f-968c46815228","added_by":"auto","created_at":"2021-10-25 15:44:46","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":430695,"visible":true,"origin":"","legend":"AHE and PHE resistances measured for various doses. (a) Hall resistance loops of dose amount of 30 ions/nm2 in ϕ = 10˚ - 40˚. The oblique magnetic field (θB = 80˚) is applied to obtained mixed Hall resistances signals. (b) AHE contribution and (c) RH as a function of sin2 θM to extract the PHE contribution from the slopes of those plots. The measurements results are obtained for various doses at ϕ = 40˚ at θB = 80˚. (d) Resulting RAHE and RPHE values and (e) its ratio, RPHE/RAHE, at each dose.","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/a9faa90c090be5971fd4e277.jpg"},{"id":14874893,"identity":"3cde7f7c-d149-4262-8087-b4cfc8f96f25","added_by":"auto","created_at":"2021-10-25 15:47:46","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":565264,"visible":true,"origin":"","legend":"Please see the Manuscript file for the complete figure caption","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/279f7c55e67e8525f123f792.jpg"},{"id":14874603,"identity":"fdcedf27-0f98-4279-866f-dd5a8699192c","added_by":"auto","created_at":"2021-10-25 15:44:46","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":312798,"visible":true,"origin":"","legend":"Resistivity changes of Platinum single layer for various doses and its comparison with SHA. (a) Measured Platinum single layer resistivity at 300 K and 5 K as function of dose amounts. (b) The ratios of temperature coefficient αTemp and RRR comparing to the pristine sample values (c) Comparison of θSH and resistivities at 300 K for various doses. Red solid line is linear fitted line of θSH with platinum resistivity. (d) Calculated power consumption ratio at each dose comparing pristine sample.","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/9c2cfb42abf94c1babe6489d.jpg"},{"id":18775366,"identity":"bb0e556b-2bf4-4763-a2df-2b7f3270d889","added_by":"auto","created_at":"2022-03-02 12:19:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":793132,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/5b918c7e-4df4-4e50-ac3e-19057840f345.pdf"},{"id":14874606,"identity":"6bf13253-9925-47ed-8a2d-3ea89716d846","added_by":"auto","created_at":"2021-10-25 15:44:46","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":746088,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-997332/v1/0c7d1018ccd86dee38855182.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eImproved Spin-orbit Torque Induced Magnetization Switching Efficiency by Helium Ion Irradiation\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSpin-orbit torque (SOT) induced magnetization switching is a perspective phenomenon to magnetic material based devices because of its potential application to the non-volatile magnetic random access memory (MRAM) and in-logic memory devices. SOT devices have two main benefits compare to the spin transfer torque (STT) MRAM. First, SOT switching is much faster (~ 1 ns) than STT-MRAM (~ 10 ns). Second, SOT-MRAM have reading path separated from the writing path, it is expected that more stable devices are possible and more margins in the reading and writing currents. In SOT switching, there are two essential ingredients: structural inversion symmetry breaking and strong spin-orbit coupling (SOC). A heavy metal (HM) / ferromagnetic metal (FM) bilayer structure satisfies those requirements. When charge current passes through the HM, the spin current is created inside of HM and injected into the FM by spin Hall effect (SHE)\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e and/or the Rashba effect can create non-zero effective field at the interfaces\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. For developing more effective SOT induced magnetization switching, many relevant parameters like spin Hall angle (SHA, \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e)\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, magnetic anisotropy field\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e and Dzyaloshinskii-Moriya (DM) interaction\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e are under the investigation. Among them, \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e, a ratio of spin current to the charge current densities, is a vital parameter as indicators of converting efficiency from electric charge to spin current densities by SHE in HM. The \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e is one of the key players on SOT induced switching since the magnitude of SOT is proportional to the spin current. Therefore, \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e value has been investigated heavily in various HMs, like Ta (~0.15)\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, β-W (~0.33)\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e and Pt (~0.1)\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eSince the discovery of SOT, intensive efforts to enhance and control the strength of SOT are conducted by annealing\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e, resistivity control of HM layer\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, normal metal (NM) insertion\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, alloying\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, interface modifying\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, and ion irradiation\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Among them, the method of irradiating Helium ion is known as leading a structural rearrangement while maintaining the overall atomic layer districts in the multi-stacked structure\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e even if no ions remain in the sample due to the long penetration depth (\u0026gt; 50 nm)\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Ion irradiation induced structural reorganization affects layers and interfaces, resulting in the coercivity and anisotropy field change\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, domain wall (DW) pinning site creation\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, modulating DM Interaction\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, and performing magnetic skyrmions\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. This characteristic is also evident in the case of SOT, so it has been observed in various SOT relevant effects such as reduction of switching current by SOT\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, influence on DW dynamics\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, and multi-level state\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. However, none of the previous studies about Helium ion irradiation modifying SOT phenomena have been paid attention in analyzing its origins by separating the properties of HM and FM layer.\u003c/p\u003e \u003cp\u003eHere, we successfully distinguished the effects of ion irradiations on HM/FM bilayer system, as changes of \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e and PMA strength in HM and FM layer. We prepared Pt(5)/Co(0.8)/MgO(2) structure samples and irradiated Helium ions in various doses. After Helium ions irradiations, we measured the critical current for SOT induced switching with various in-plane field. We found that the switching current decreases from 16.1 to 11.2 mA as increasing dose amounts from 0 to 30 ions/nm\u003csup\u003e2\u003c/sup\u003e with the in-plane field of 3.1 kOe. For understanding the decrease of switching current, we also measured the first and second order uniaxial anisotropy fields, and \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e determined by the harmonic Hall measurement method. By careful analysis including the second order uniaxial anisotropy field contributions, we extracted magnetization polar angular dependent effective field caused by SOT for each dose and \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e from \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e. Furthermore, we measured the effect of the dose amount on the resistivities of single Pt layers and confirmed the relation between resistivity and \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e. Based on our analysis, the reduction of the switching current partially ascribes to the reduced anisotropy field from 13.7 to 8.5 kOe (38.0 %) and improved \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e from 0.096 to 0.132 (27.2 %). Here, it must be mentioned that the reduction rate of switching current (30.4%) is smaller than expected reduction rate when we consider the magnetic anisotropy reduction and \u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e enhancement. Nevertheless, the calculated power consumption was 87.4%, 59.6%, and 56.0% at each dose compared with the non-irradiated sample, indicating that Helium ion irradiation can contribute to better SOT device fabrication.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eWe deposited Pt(5 nm)/Co(0.8 nm)/MgO(2 nm) heterostructure sample using magnetron sputter and patterned as 10 \u0026micro;m width Hall bar structure by photolithography technique. In Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea, the sample structure, coordinate systems, and Helium ion irradiation area are depicted. \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e is the polar angle between magnetization direction and z-axis, \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eB\u003c/em\u003e\u003c/sub\u003e is the polar angle between the external magnetic field and z-axis, and \u003cem\u003eϕ\u003c/em\u003e is azimuthal angle from x-axis, and here we ignore the angle differences between the external magnetic field and magnetization directions in the azimuthal angle because of the negligible in-plane anisotropy. After Hall bar fabrication process, Helium ion is irradiated in vertical direction with sample plane having acceleration energy of 30 keV, beam current of 5.5 pA, and dose from 0 to 30 ions/nm\u003csup\u003e2\u003c/sup\u003e with step of 10 ions/nm\u003csup\u003e2\u003c/sup\u003e. Irradiation area covers whole Hall cross for avoiding signal mixing errors by signal differences between irradiation and non-irradiation area as shown red dotted rectangle in Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea (more explanation in Supplementary Figure S1).\u003c/p\u003e\n\u003cp\u003eMeasurement of SOT induced magnetization switching includes three sequences: initialization, SOT writing by pulse current, and reading from Hall resistance measurement. Firstly, sample is under strong enough +z-axis (-z-axis) direction external field to saturate the magnetization in up (down) direction as initial state. After initialized, the current pulse is injected with pulse amplitude (\u003cem\u003eIp\u003c/em\u003e) from -25 to 25 mA (25 to -25 mA) with 1 mA step. During the current pulse injection in x-axis direction in-plane magnetic field is applied to ensure deterministic switching. And the Hall resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e) is measured in the middle of each pulse injection with 100 \u0026micro;A magnitude direct current (DC). Here, we should mention that the \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e is unit value calculated from measured Hall voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e) dividing with magnitude of reading current. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e results as a function of Ip with the previous procedure shows typical hysteresis loops, as shown in Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb-\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec, and it indicates SOT induced magnetization switching in PMA system. Here, the shown hysteresis loops in Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb are in case for dose amount of 30 ions/nm\u003csup\u003e2\u003c/sup\u003e. It is well known that higher in-plane field make switching more easily, but we observe that Helium ion irradiation also reduces the switching current. The SOT driven magnetization switching hysteresis loops for various doses with a fixed 2.2 kOe external in-plane field is shown in Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec. In Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed, the switching currents from magnetization switching loops at each dose and external magnetic field are depicted. In Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed, we found two features. Firstly, in small field region (0.7 kOe), rapid increase of switching current appears. We expect that this increase is caused by the nucleation of multi-domain states during SOT induced magnetization switching process (see the Supplementary Figure S2a for more details). Because of the multi-domains under small field, it is hard to compare the switching current in higher field region directly so that we will not pay attention much. The second feature is main finding of this work in larger field regions (\u0026ge;1.2 kOe). We found that the switching current is reduced by increasing dose amounts. And at same dose amount, the switching current have linear relation with the external in-plane field strength under the sufficiently smaller in-plane field comparing 1st order effective anisotropy field, which is well-known behavior following \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({J}_{C}=\\frac{2e}{\\hslash }\\frac{{M}_{s}{t}_{F}}{{\\theta }_{SH}}\\left(\\frac{{H}_{K,eff}}{2}-\\frac{{H}_{x}}{\\sqrt{2}}\\right)\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. And here, e is charge of electron, \u003cem\u003eℏ\u003c/em\u003e is Planck constant, \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e is saturation magnetization, \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e is thickness of FM layer, \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e is the 1st order anisotropy field and \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e is in-plane external magnetic field parallel with current. In order to get better insight of the Helium irradiations effect, we show the switching current reduction ratio at each dose compared with the pristine sample (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\left|\\left({I}_{P.crit}-{I}_{P,crit}^{Dose 0}\\right)/{I}_{P,crit}^{Dose 0}\\right|\\times 100 \\%\\)\u003c/span\u003e\u003c/span\u003e) as in Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ee. Result shows that the switching current reduction has increasing tendency with dose amount for in-plane external field. The exceptional dependence for small field (0.7 kOe) probably ascribe to the formation of multi-domain state as seen in Supplementary Figure S2b. The reduction ratio appears largely at external field of 3.1 kOe about 14.2%, 25.5%, and 30.3% at dose of 10, 20, and 30 ions/nm\u003csup\u003e2\u003c/sup\u003e, respectively. Here, the possible physical origins of the switching current reduction can be the enhanced \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e of Pt layers, and/or it can be the decrease of the effective anisotropy field of FM layer. We will discuss more details later.\u003c/p\u003e\n\u003cp\u003eTo understand the more details of switching behavior, the effects of Helium ion irradiation on the magnetic anisotropy fields are investigated. We conducted Anomalous Hall effect (AHE) measurement by swapping the external magnetic field in z-axis direction to obtained normalized Hall resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(H\u003c/em\u003e\u003csub\u003e\u003cem\u003eext\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e)/R\u003c/em\u003e\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e(H\u003c/em\u003e\u003csub\u003e\u003cem\u003eext\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e=0 Oe)\u003c/em\u003e) hysteresis loops, because the AHE signal is proportional to the z-component of magnetization. The normalized AHE hysteresis loops in Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea shows strong enough PMA for all samples. And each coercivity is decreasing (~ 34 %) from 271 Oe to 178 Oe as shown in Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb by increasing dose amounts. In order to obtain the 1st and 2nd order anisotropy fields (\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,2\u003c/em\u003e\u003c/sub\u003e) by using generalized Sucksmith-Thompson (GST) method (see Supplementary Figure S3), we measured normalized AHE by applying in-plane field (\u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e) along the current direction as seen in Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec. Here, it must be mentioned that the obtained 1st order anisotropy fields are the effective anisotropy including demagnetization effect, not pure anisotropy field in GST method. The \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,2\u003c/em\u003e\u003c/sub\u003eare shown in Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed as a function of dose. By increasing dose amount from 0 to 30 ions/nm\u003csup\u003e2\u003c/sup\u003e, \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,2\u003c/em\u003e\u003c/sub\u003edecrease 38.2%, and 27.5%, respectively. We speculate that decrease is mainly caused by interface modulation from Helium ion irradiation process, since the surface anisotropy energy is very sensitive on the quality of the interface between HM and FM layers. Although it is hard to classify and/or probe the effect of the structural modulation caused by the Helium ion irradiation, we can claim that he anisotropic field as well as the coercivity field can be reduced by the Helium ion irradiation. The magnitude of \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,2\u003c/em\u003e\u003c/sub\u003eis only less than half (40.1 %) compared with the \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e, however, the SOT analysis without consideration of \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,2\u003c/em\u003e\u003c/sub\u003e may lead incorrect results\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eNot only the anisotropy characteristics, but also an important parameter in SOT induced magnetization reversal is \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e. The harmonic Hall signal analysis is frequently used method for calculating \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e as well as extracting SOT driven effective fields\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. It is well known that the SOT has two contributions acting on different directions, so called field-like torque (FLT, \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eFL\u003c/em\u003e\u003c/sub\u003e) in transverse direction and damping-like torque (DLT, \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e) effective field in longitudinal direction, consideration of AHE and PHE resistances are necessary for obtaining correct results. In Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, the measured Hall resistance loops are shown at \u003cem\u003eϕ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10 to 40\u0026deg; with fixed \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eB\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;80\u0026deg; for dose amount of 30 ions/nm\u003csup\u003e2\u003c/sup\u003e sample. Since the AHE and PHE contribute to the measured Hall signal as following the equation\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e,\u003c/p\u003e\n\u003cdiv class=\"Equation\" id=\"Equ1\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$${V}_{H}={I}_{0}{R}_{0}=\\frac{{I}_{0}{R}_{AHE}}{2}\\text{cos}{\\theta }_{M}+\\frac{{I}_{0}{R}_{PHE}}{2}{\\text{sin}}^{2}{\\theta }_{M}\\text{sin}2\\varphi$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe clear asymmetries are observed for the Hall loops in Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea in the large field. The asymmetry also increases because of the larger PHE contribution for large \u003cem\u003eϕ\u003c/em\u003e. And by adding and subtracting divided asymmetric Hall loop between +B to -B part and -B to +B part, one can separate the contributions of AHE and PHE as seen in Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb and Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec, respectively. Details of extracting method for AHE and PHE resistances is explained in Supplementary Figure S4. Here, Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb and Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec show the data at the angle of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eB\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;80\u0026deg; and \u003cem\u003eϕ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;40\u0026deg; at each dose amount. The AHE resistance can be calculated using AHE contribution at \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eB\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg;, corresponding to zero external in-plane field, and the PHE resistance can be also calculated taking linear plot on the PHE contribution from the slope of sin\u003csup\u003e2\u003c/sup\u003e\u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e, in Equation (\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). From those measurement analyses, the calculated AHE and PHE resistances are shown in Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed together. R\u003csub\u003eAHE\u003c/sub\u003e increased from 1.09 to 1.20 Ω (9.8 %) with increasing dose amounts, while R\u003csub\u003ePHE\u003c/sub\u003e varied within the range of 0.37 to 0.34 Ω. Since the ratio of \u003cem\u003eR=R\u003c/em\u003e\u003csub\u003e\u003cem\u003ePHE\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e/R\u003c/em\u003e\u003csub\u003e\u003cem\u003eAHE\u003c/em\u003e\u003c/sub\u003e has an important role in analysis of the harmonic Hall measurement result, we calculated the ratio and it changes from 0.34 to 0.29 at dose of 0 and 30 ions/nm\u003csup\u003e2\u003c/sup\u003e, as depicted in Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee. It must be mentioned that the variation of R with Helium ion irradiation is not significant comparing to other physical quantities. One possible explanation is that the bulk magnetic properties are relatively insensitive on the Helium ion irradiation, while the surface properties, such as surface anisotropy, are more sensitive.\u003c/p\u003e\n\u003cp\u003eTo obtain the \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e or SOT induced effective fields, we measure harmonic Hall with alternating current (AC) of 5.5 mA peak amplitude and 401 Hz frequency (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003eAC\u003c/em\u003e\u003c/sub\u003e = \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e sin2\u0026pi;\u003cem\u003eft\u003c/em\u003e). Because the harmonic Hall measurement is influenced by the Joule heating effect caused by current flow, we follow the four-direction method for eliminating some thermoelectric artifacts\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The 1st and 2nd harmonic Hall loop is measured swapping magnetic field with fixed \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eB\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;85\u0026deg; and \u003cem\u003eϕ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg; for \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eϕ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;90\u0026deg; for \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eFL\u003c/em\u003e\u003c/sub\u003e measurements. Each Hall loop result is shown in Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea-\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec, respectively. Here, the 1st and 2nd harmonics are measured simultaneously with two lock-in amplifiers at each \u003cem\u003eϕ\u003c/em\u003e and dose amounts. Harmonic Hall voltage signal under AC follows the equation,\u003c/p\u003e\n\u003cdiv class=\"Equation\" id=\"Equ2\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$${V}_{H}={I}_{o}{R}_{H}={V}^{1\\omega }\\text{sin}\\left(\\omega t\\right)-{V}^{2\\omega }\\text{c}\\text{o}\\text{s}\\left(2\\omega t\\right)$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eAlthough 1st voltage has almost same signal at each \u003cem\u003eϕ\u003c/em\u003e, 2nd voltage has completely different signals as shown Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb and Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec. These results are come from the different contribution between DLT and FLT. The 2nd order harmonic Hall voltage at each \u003cem\u003eϕ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0\u0026deg; and 90\u0026deg; with consideration of 2nd order PMA energy follow the expression\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e,\u003c/p\u003e\n\u003cdiv class=\"Equation\" id=\"Equ3\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$${V}_{x}^{1\\omega }={V}_{y}^{1\\omega }={V}_{AHE}\\text{cos}{\\theta }_{M}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Equation\" id=\"Equ4\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e$${V}_{x}^{2\\omega }=\\frac{{V}_{AHE}}{2} \\left({A}_{1}{\\Delta }{H}_{DL}-{B}_{1}{\\Delta }{H}_{FL}\\right)$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Equation\" id=\"Equ5\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e$${V}_{y}^{2\\omega }=\\frac{{V}_{AHE}\\text{cos}{\\theta }_{M}}{2} ({B}_{1}{\\Delta }{H}_{DL}-{A}_{1}{\\Delta }{H}_{FL})$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Equation\" id=\"Equ6\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e$${A}_{1}\\equiv \\frac{\\text{s}\\text{i}\\text{n}{\\theta }_{M}}{{H}_{K,eff}\\text{cos}2{\\theta }_{M}-{H}_{K,2}\\text{sin}{\\theta }_{M}\\text{sin}3{\\theta }_{M}+{H}_{ext}\\text{cos}\\left({\\theta }_{M}-{\\theta }_{H}\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"Equation\" id=\"Equ7\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e$${B}_{1}\\equiv \\frac{R\\text{s}\\text{i}{\\text{n}}^{2}{\\theta }_{M}}{{H}_{ext}\\text{sin}{\\theta }_{H}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eFollowing the Equation (\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) to (\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e), we can rewrite DLT and FLT effective fields (\u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eFL\u003c/em\u003e\u003c/sub\u003e) as function of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e from the measured harmonic Hall voltages as shown in Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed and Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee, respectively. Here, \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e can be calculated using experimentally obtained the 1st order harmonic Hall signal at each dose with Equation (\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The results show the different dose dependences on \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eFL\u003c/em\u003e\u003c/sub\u003e with \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e. When the near of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;15\u0026deg;, corresponding magnetization angle at external magnetic field of 3.1 kOe in 0 ions/nm\u003csup\u003e2\u003c/sup\u003e, \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e has small increasing tendency as shown in the inset in Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed but \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eFL\u003c/em\u003e\u003c/sub\u003e has decreasing tendency at its magnitude according to dose amount. However, when \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;15\u0026deg;, both effective fields show great increase and complex behavior having a maximum peak point at \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e of range from 40\u0026deg; to 45\u0026deg;. According to simple macro-spin SOT model\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, there is no magnetization direction dependence on both effective SOT fields. However, there are much experimental evidences of the magnetization direction dependence on the effective SOT fields\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The higher order term of SOT can be one of the possible origins of complex angular dependence. According to Ref.30, the high order term of SOT is non-negligible and may cause complex angular dependence. In addition, if Helium ion irradiation modulates the higher-order term of the SOT just similar as the higher-order term of the PMA, the change in angular dependence can be estimated as a phenomenon caused by the Helium ion irradiation. Furthermore, another possible approach explaining such magnetization direction dependent effective SOT fields is from the framework of distorted Fermi surface\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. The \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e dependent effective fields in Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed and Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee are rather complicated angular dependence compared with the theoretical results are based on the free-electron like model Hamiltonian with exchange coupling and Rashba effect. The experimental results reflect realistic band structures so that the more complex angular dependent explanation is acceptable. It is hard to analysis the exact origins separately. However, it is also true that the varying angular dependent effective fields by degree of ion irradiation has been experimentally observed as seen in Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed and Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee. And it is worth to note that if \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,2\u003c/em\u003e\u003c/sub\u003e is not considered in the calculation, the result has quite different tendency with Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed-\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee, suggesting the critical role of the 2nd order anisotropy in precise analysis of harmonic Hall measurement in all range of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e (see the Supplementary Figure S5).\u003c/p\u003e\n\u003cp\u003eBecause \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e is one of the most important material parameters for SOT based devices, understanding the correlation between ion irradiation induced \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e variation and HM layer state is important. In order to reveal the effect of the Helium ion irradiation on HM layer only, we irradiated the Helium ion on single Pt layer with thickness of 5 nm as same conditions introduced in sample fabrication description. We used the 4-probe measurement technique for measuring resistance with temperature range of 5 K to 225 K and calculated resistivity using sample geometry information with measured resistance. Here, the resistivity curve and the method of calculating resistivity at 300 K are explained in Supplementary Figure S6a. The resistivity of Pt (\u003cem\u003e\u0026rho;\u003c/em\u003e\u003csub\u003e\u003cem\u003ePt\u003c/em\u003e\u003c/sub\u003e) at 300 K and 5 K is shown in Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea and we can observe the increasing resistivity according to dose amount, 43.4 to 47.8 \u0026micro;Ω∙cm (109%) in 5 K and 56.8 to 60.9 \u0026micro;Ω∙cm (107%) in 300 K comparing 0 ions/nm\u003csup\u003e2\u003c/sup\u003e and 30 ions/nm\u003csup\u003e2\u003c/sup\u003e. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb displays the changed ratio of temperature coefficient (\u003cem\u003e\u0026alpha;\u003c/em\u003e\u003csub\u003e\u003cem\u003eTemp\u003c/em\u003e\u003c/sub\u003e), following \u003cem\u003e\u0026rho;\u0026thinsp;=\u0026thinsp;\u0026rho;\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e(1\u0026thinsp;+\u0026thinsp;\u0026alpha;\u003c/em\u003e\u003csub\u003e\u003cem\u003eTemp\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e∙ (T-T\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e)\u003c/em\u003e at linear resistivity increasing region (\u003cem\u003eT\u003c/em\u003e \u0026gt; 50 K), and residual-resistivity ratio (\u003cem\u003eRRR\u003c/em\u003e), comparison of resistivities between 300 K and 5 K in here. We can find the decreasing tendency of \u003cem\u003e\u0026alpha;\u003c/em\u003e\u003csub\u003e\u003cem\u003eTemp\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eRRR\u003c/em\u003e both, it can be interpreted as increased influence of impurity at higher dose. Because the collision time is inversely proportional to the impurity density, decrease of \u003cem\u003e\u0026alpha;\u003c/em\u003e\u003csub\u003e\u003cem\u003eTemp\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eRRR\u003c/em\u003e value imply that the Helium ion irradiation makes extra scattering sources by structural distortion in Pt layer. The Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec shows the resistivity dependence of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e, and it can be calculated with \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e at each dose value using following equation\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e,\u003c/p\u003e\n\u003cdiv class=\"Equation\" id=\"Equ8\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e$${\\theta }_{SH}=\\frac{2\\text{e}}{\\text{\\hslash }}\\frac{{M}_{s}{t}_{F}{A}_{HM}}{{I}_{0}}\\varDelta {H}_{DL}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eHere, A\u003csub\u003eHM\u003c/sub\u003e is the cross section area of flowing current into HM. We assume that the influence of irradiation on \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e, and \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003eHM\u003c/em\u003e\u003c/sub\u003e is small enough to ignore, because the irradiated dose amount is scarce to cause interlayer deformation\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. So, we calculated the \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e with \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e = 1100 kA m\u003csup\u003e-\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e = 0.8 nm, \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003eHM\u003c/em\u003e\u003c/sub\u003e = 10 \u0026micro;m \u0026times; 5 nm and \u003cem\u003e\u0026Delta;H\u003c/em\u003e\u003csub\u003e\u003cem\u003eDL\u003c/em\u003e\u003c/sub\u003e when \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;15\u0026deg; at each dose amount using Equation (\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). Error bar can be calculated as the averaged of values of the front and rear data starting from \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eM\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;15\u0026deg;. It is found that \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e has linear relation with increased resistivity by Helium ion irradiations, as well reported\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. The \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e increases 0.096 to 0.132 with resistivity growth from 56.8 to 60.9 \u0026micro;Ω∙cm in 300 K, about 5 - 6 times greater than resistivity of bulk Pt (10.6 \u0026micro;Ω∙cm in 20 ℃) in literature\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. This result suggests that Helium ion irradiation process makes extra scattering sources, and they raise the resistivity of HM layer. And the extra scattering sources cause improvement of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e, resulting in more effective switching of the magnetization by SOT. Although the energy efficiency in view of operating the device is slightly worse due to the ion irradiation induced resistance increasement, the improved \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e ratio is ~ 4 times greater compared with resistivity increasement ratio. In terms of power (\u003cem\u003eP=R\u003c/em\u003e\u003csub\u003e\u003cem\u003esample\u003c/em\u003e\u003c/sub\u003e\u003cem\u003eI\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e) consumption, the change in resistance and SHA has an inverse relationship. As a result, only 87.4%, 59.6%, and 56.0% of power consumption is expected at 10, 20, and 30 ions/nm\u003csup\u003e2\u003c/sup\u003e, respectively. (See Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed) Here, the \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003esample\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e are normalized resistance of HM and normalized current by \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e at each dose. Therefore, it means that Helium ion irradiation enables more efficient data writing in terms of energy consumption. And it is worth mentioning that the critical switching current equation shown in ref.28 does not match with our actual experimental value except only linear relationship with in-plane field. We expect because the formula is based on the macro spin model as like well-known Brown paradox\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Furthermore, there are reports that it does not match the actual value in the micron scale sample\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. That\u0026rsquo;s why we obtained \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e from the spin-orbit torque effective field measurement (see Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec), not from the switching current density. Nevertheless, it is clear that the Helium ion irradiation leads to a decrease in the \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e, an increase in the \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e, and the more efficient the SOT induced magnetization switching.\u003c/p\u003e\n\u003cp\u003eIn summary, we observe that Helium ion irradiation can properly reduce SOT induced switching current in Pt(5)/Co(0.8)/MgO(2) structure. The reduction appears 14.2%, 25.5%, and 30.3% at dose of 10, 20, and 30 ions/nm\u003csup\u003e2\u003c/sup\u003e comparing with the pristine sample under the in-plane external magnetic field of 3.1 kOe. For understanding of physical reasons of decreasing tendency of the switching current, we considered two main possible origins of reduction, \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e. From AHE measurement and GST method, we can extract \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e and it decreases from 13.7 to 8.5 kOe (38.2%) comparing dose 0 and 30 ions/nm\u003csup\u003e2\u003c/sup\u003e. Not only \u003cem\u003eH\u003c/em\u003e\u003csub\u003e\u003cem\u003eK,eff\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e also increase from 0.096 to 0.132 (27.2%). Furthermore, it is revealed that improvement of \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e is consequence of increase of Pt resistivity by ion irradiation process. Although the power consumption is slightly worse due to the increase of the resistance, the decreased critical current caused by the improved \u003cem\u003e\u0026theta;\u003c/em\u003e\u003csub\u003e\u003cem\u003eSH\u003c/em\u003e\u003c/sub\u003e has a greater impact in power consumption. As a result, the ratio of power requiring for operation of device is calculated to consume only about 56.0% for switching at 30 ions/nm\u003csup\u003e2\u003c/sup\u003e compared to pristine sample, and this successful analysis on Helium ion irradiation induced modulation of SOT effect can be expected to improve efficiency of SOT based spintronic devices engineering.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch2\u003eThin film preparation and fabrication process\u003c/h2\u003e\n\u003cp\u003eThe sample preparation process includes three steps, firstly Hall bar photolithography and deposition, secondly electrode fabrication, and Helium ion irradiation at last. This section will only explain up to step 2, and step 3 will be explained in later paragraph (See the Helium ion microscope in \u003cspan class=\"InternalRef\"\u003eMethods\u003c/span\u003e section). The sample is fabricated with lift-off process using photolithography and magnetron sputtering system. Normal metal layer and oxide layer is deposited using DC and AC power with stack of Pt(5)/Co(0.8)/MgO(2) on single surface polished Si substrate having 300nm thickness SiO\u003csub\u003e2\u003c/sub\u003e oxidated surface. The patterned Hall bar geometry consists of the current line of 10 \u0026micro;m width and 40 \u0026micro;m length and voltage line of 3 \u0026micro;m width 16 \u0026micro;m length. This geometry represses the offset error caused by sample shape. After deposition and patterning of sample, we deposit the electrode with stack of Ta(5)/Cu(50) for electric measurement.\u003c/p\u003e\n\u003ch2\u003eHelium ion microscope\u003c/h2\u003e\n\u003cp\u003eHIM (Helium ion microscope, Carl Zeiss/ORION NanoFab), using high energy ionized Helium, is one of the brand-new microscopic techniques. Using HIM, we can obtain more detailed image in nano-scale structure compared with Gallium ion or electron based microscope owing to its penetration characteristic of high energy Helium ion\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. But for utilizing HIM, we must make trimer, as the state of leaving only three atoms at the end of tip, stability and duration problems are remained. Even in such problems, the high penetration characteristic and low diffraction limitation of HIM come to be a big attraction. Because the HIM have low convergence angle, long best focus length and high penetration depth, more than few tens of nanometer scale, it also can be used as precise atomic structure destruction method. We expose the Helium ion with normal direction of sample plane with dose value of 0 to 30 ions/nm\u003csup\u003e2\u003c/sup\u003e at energy of 30 keV and current of 5.4 ~ 5.5 pA. The exposure process can be conducted from few hundred micron to few tens of nanometer size, and we conducted with area of 20 \u0026micro;m \u0026times; 20 \u0026micro;m. The HIM is in the Central Core Research Facility center in DGIST, Korea.\u003c/p\u003e\n\u003ch2\u003eTransport measurement system with DC and AC current\u003c/h2\u003e\n\u003cp\u003eFor measuring magnetic properties, we use the DC \u0026amp; AC source (Keithley, 6221), nano-voltmeter (Keithley, 2182A), and lock-in amplifiers (Zurich Inst. SR830). Each equipment is connected to sample using customized PCB in the 2-axis rotational holder and the direction of magnetic field is controlled by rotating holder in prefer direction using motors. For measuring SOT induced magnetization switching, we use the current source for injecting pulse and nano-voltmeter for measuring Hall voltage. The magnetization is initialized to +z direction (or -z direction) using magnetic field and switching is induced under in-plane magnetic field using sweep mode of DC \u0026amp; AC source. Comparing SOT induced magnetization switching measurement, the harmonic Hall measurement use different voltmeter, not nano-voltmeter but two lock-in amplifiers for detecting AC based Hall signals. One lock-in amplifier detects the 1st harmonic signal, and the other detects the 2nd signal. All lock-in amplifiers are connected to sample with same voltage line, so the 1st and 2nd harmonic signal is measured simultaneously.\u003c/p\u003e\n\u003cp\u003eFor temperature dependent measurement, we use the cryostat to be able to connect with nano-voltmeter and current source. The cryostat chamber also can be connected to customized PCB to instruments. The resistance is measured using 4-probe measurement with reading current of enough small current and sample atmosphere temperature can vary from 5 K to 275 K with gap of 0.25 K using chamber heater and Helium compressor system. Here, all current and voltage equipment is connected with sample using Bayonet Neill\u0026ndash;Concelman cable for repressing noises.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThis work is supported by the National Research Foundations of Korea (NRF-2015M3D1A1070465, NRF-2021R1A2C2007672, NRF-2020M3F3A2A02082437, NRF-2021M3F3A2A01037525, NRF-2018R1A6A3A11041061).\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eAuthor contributions statement\u003c/h2\u003e\n\u003cp\u003eK.-S.L. and C.-Y.Y. conceived the projects; Sample fabrication was done by S.A. and J.-A.K; the measurements were performed by S.A., E.B.; Data analysis and manuscript preparation were done by S.A., K.-S.L., and C.-Y.Y.; The study was supervised by C.-Y.Y.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eAdditional information\u003c/h2\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLiu, L., Lee, O. 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Lett\u003c/em\u003e, \u003cb\u003e109\u003c/b\u003e, 142405 (2016).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"spin-orbit torque (SOT), magnetization switching efficiency, Helium ion irradiation","lastPublishedDoi":"10.21203/rs.3.rs-997332/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-997332/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIncreasing the efficiency of spin-orbit torque (SOT) is of great interest in spintronics devices because of its application to the non-volatile magnetic random access memory and in-logic memory devices. Accordingly, there are several studies to alter the magnetic properties and reduce the SOT switching current with Helium ion irradiation, but previous researches are focused on its quantitative changes only. Here, the authors observe the reduction of switching current and analyze the origins of Helium ion irradiation induced SOT switching current reduction. The first is from improved spin Hall angle caused by the resistivity change of heavy metal layer and second is from the reduction of surface anisotropy energy at interface between heavy metal and ferromagnet. The result shows that switching current is reduced about ~30.3% at dose of 30 ions/nm\u003csup\u003e2\u003c/sup\u003e and relevant parameter change is shown as improved spin Hall angle from 0.096 to 0.132 and reduced anisotropy field from 13.7 to 8.5 kOe. Altogether, the power consumption ratio is calculated based on the derived parameter and result shows that requiring power reaches only 56.0% at 30 ions/nm\u003csup\u003e2\u003c/sup\u003e. This analysis suggests that more efficient SOT device engineering is possible by Helium ion irradiation.\u003c/p\u003e","manuscriptTitle":"Improved Spin-orbit Torque Induced Magnetization Switching Efficiency by Helium Ion Irradiation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-10-25 15:44:44","doi":"10.21203/rs.3.rs-997332/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2021-11-22T05:53:28+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"3943456e-505a-4f12-9757-5bcaf057834e","date":"2021-10-31T12:01:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2021-10-28T15:47:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"017248fd-d573-48c2-b037-2cfbd62d902c","date":"2021-10-23T01:17:43+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2021-10-22T16:12:52+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2021-10-22T16:06:13+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2021-10-22T12:17:50+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2021-10-22T12:08:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2021-10-20T01:52:40+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c3d6de19-1069-4d16-9708-575aca5100ac","owner":[],"postedDate":"October 25th, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":8081787,"name":"Scientific Communication"},{"id":8081788,"name":"Materials Chemistry"},{"id":8081789,"name":"Materials Engineering"}],"tags":[],"updatedAt":"2022-03-02T12:19:48+00:00","versionOfRecord":{"articleIdentity":"rs-997332","link":"https://doi.org/10.1038/s41598-022-06960-8","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2022-03-02 12:19:48","publishedOnDateReadable":"March 2nd, 2022"},"versionCreatedAt":"2021-10-25 15:44:44","video":"","vorDoi":"10.1038/s41598-022-06960-8","vorDoiUrl":"https://doi.org/10.1038/s41598-022-06960-8","workflowStages":[]},"version":"v1","identity":"rs-997332","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-997332","identity":"rs-997332","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}