Unusual d-electron heavy-fermion behaviour in f-electron ferromagnetic antiperovskite Gd3SnC

Unusual d-electron heavy-fermion behaviour in f-electron ferromagnetic antiperovskite Gd3SnC | 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 Article Unusual d-electron heavy-fermion behaviour in f-electron ferromagnetic antiperovskite Gd 3 SnC Joonho Bang, Jongho Park, Kimoon Lee, Minsoo Kim, Wonshik Kyung, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-336915/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Inverted structures of common crystal lattices, referred to as antistructures, are rare in nature due to their thermodynamic constraints imposed by the switched cation and anion positions in reference to the original structure. However, a stable antistructure formed with mixed bonding characters of constituent elements in unusual valence states can provide unexpected material properties. Here, we report a heavy-fermion behaviour of ferromagnetic gadolinium lattice in Gd 3 SnC antiperovskite, contradicting the common belief that ferromagnetic gadolinium cannot be a heavy-fermion system. The specific heat shows an unusually large Sommerfeld coefficient of ~ 1114 mJ⋅mol − 1 ⋅K − 2 with a logarithmic behaviour of non-Fermi-liquid state. We demonstrate that the heavy-fermion behaviour in the non-Fermi-liquid state appears to arise from the hybridized electronic states of gadolinium 5d-electrons participating in metallic Gd–Gd and covalent Gd–C bonds. These results accentuate unusual chemical bonds in CGd 6 octahedra with the dual characters of gadolinium 5d-electrons for the emergence of heavy-fermions. Magnetics Materials and Devices Soft Condensed-matter Physics Hard Condensed-matter Physics stable antistructures heavy-fermion behaviour ferromagnetic gadolinium lattice Gd3SnC antiperovskite Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The crystal structure constructed with chemical bonds of constituent elements determines the electronic structure of a material and its properties. In a fixed symmetry, electronically inverted structures with switched crystallographic positions of cations and anions from the original structure often have a reversed compositional ratio, which necessarily forms a different coordinated substructure with additional bonding characters and can lead to an exotic electronic structure. However, in general, such antistructures composed of the same constituent elements in the reversed compositional ratio are thermodynamically unstable. Indeed, due to the thermodynamic constraints, antistructures found in several classes of materials are constructed by subsidiary chemical bonds of different constituent elements from original structures. This appears, for example, in the Cd-deficient Cd 3 As 2 antifluorite 1 , which has a strong covalent bonding nature in a reversed compositional ratio from the ionic CaF 2 fluorite. It is noteworthy that the Cd 3 As 2 antifluorite exhibits exotic properties: a three-dimensional topological Dirac band 1 – 3 along with negative magnetoresistance 4 , anomalous Hall effect 5 , and pressure-induced superconductivity 6 . ABX 3 perovskites, as the largest family of crystalline materials, also have their counterpart antistructures, A 3 BX antiperovskites 7 . In contrast to the perovskite compounds constructed by the ionic bonds of constituent elements in stable valence states, the antiperovskites have mixed bonding characters with ionic, covalent, and metallic bonds in unusual valence states 8 . However, oxide antiperovskites ( A 3 B O), antistructures of common oxide perovskites ( AB O 3 ), are hardly stabilized in ambient conditions as oxygen tends to form ionic bonds with counter-cationic A and B elements due to its large ionicity 9 . This constraint may be lifted for s-block and transition metal-based antiperovskites, in which additional covalent and metallic bonds come into play for their crystallographic stability 7 , 10 . The boundary for such stable antiperovskite compounds can be extended to f-block lanthanides, which form a crystal with various elemental groups of d-block transition metals and p-block post-transition metals 7 . Those compounds may exhibit diverse electronic properties because of the multiple bonding characters with enhanced covalency and/or metallicity. Furthermore, considering the fact that f-electrons often contribute to strongly correlated electronic properties, a variety of unconventional quantum phenomena may be anticipated in f-block antiperovskites, which can exhibit exotic electronic band structures arising from the mixed chemical bonds. However, thermodynamically stable f-block element-based antiperovskites and their novel properties have been hardly demonstrated up to now 7 , 11 . Herein, we demonstrate the unprecedented heavy-fermion behaviour of the ferromagnetic (FM) gadolinium lattice in the Gd 3 SnC antiperovskite structure and verify the crucial role of the metallic Gd–Gd and covalent Gd–C bonds of CGd 6 octahedral skeleton on an unusually hybridized Gd 5d-electrons responsible for the emergent heavy-fermions. Results Synthesis and structural analysis. Figure 1 a shows that the Gd 3 SnC crystallizes in the antiperovskite structure (space group: Pm \(\stackrel{-}{3}\) m ) with face-centred Gd and body-centred C atoms in a Sn cubic lattice, as confirmed by Rietveld analysis of powder X-ray diffraction (XRD) pattern (Supplementary Table 1). Single-phase bulk Gd 3 SnC was synthesized via the melt-solidification process at one atmosphere. This indicates the thermodynamic stability of Gd 3 SnC antiperovskite, which gets additional support from the calculated phonon dispersions having no imaginary frequency (Supplementary Fig. 1). In contrast to the ABX 3 perovskite, which has cation-centred BX 6 octahedra with ionic bonds, Gd 3 SnC has anion-centred CGd 6 octahedra with strong covalent Gd–C and metallic Gd–Gd bonds. This mixed bonding character of Gd bonds in CGd 6 octahedra results in different Gd orbital levels from those of the Gd element and its ionic compounds. As shown in Fig. 1 b, while Gd metal and Gd 2 O 3 have ordinary Gd orbital levels of Gd–Gd metallic and Gd–O ionic bonds, respectively, Gd 3 SnC has unusual energy levels for Gd orbitals due to the coexistence of metallic and covalent bonds. Considering the shorter Gd–Gd bond length (3.48 Å) in CGd 6 octahedra compared to that of Gd metal (~ 3.6 Å), one expects an enhanced metallicity and thus additional Fermi level ( E F ) crossings for Gd bands in Gd 3 SnC. On the other hand, the electronegativity difference between Gd and C is much smaller than that between Gd and O, resulting in the formation of covalent bonds between Gd and C. The energy difference between bonding and antibonding states of the covalent bonds is expected to be significantly smaller than that of ionic bonds between Gd and O. These mixed bonding characters of Gd valence orbitals in CGd 6 octahedra can lead to a peculiar molecular orbital diagram with both metallic and covalent bonds as shown in Fig. 1 b. Such observation indicates that Gd 3 SnC antiperovskite may exhibit unusual physical properties that are hardly found in elemental Gd and conventional Gd-related compounds. Tricritical ferromagnetic behaviour. Figure 2 a shows the FM phase transition of Gd 3 SnC with a Curie temperature ( T C ) of 100 K under a low magnetic field ( H ) of 0.1 kOe. In comparison to the itinerant FM in Gd metal with a T C of 297 K, different aspects of the FM order are observed 12 . A sharp increase in the magnetization ( M ) near the T C indicates a first-order transition, which is further evidenced by the hysteresis in the temperature( T ) dependence of electrical resistivity ( ρ ) (Fig. 2 e) and the negative slope in the M 2 dependence of H / M (Supplementary Fig. 2e). In addition, no structural phase transition is observed around the T C , indicating that the FM ordering occurs while preserving the antiperovskite structure (Supplementary Fig. 3). We confirm the saturation magnetic moment of ∼6.8 µ B per Gd obtained from the M – H curve (Fig. 2 b), indicating this FM state comes mostly from the seven Gd 4f-electrons. A notable aspect of M ( T ) is a slight decrease in the ZFC curve below ~ 20 K (inset of Fig. 2 a), which suggests a possible formation of singlets such as Kondo singlet 13 , 14 , as will be discussed in the following sections. This unusual behaviour in M indicates that the near E F states of Gd, which do not have contributions from fully localized f-orbitals, may be different from those of the familiar FM Gd metal and Gd-based compounds 12 , 15 . The most peculiar aspect of the FM state in Gd 3 SnC is the tricritical behaviour that appears near the boundary between the first- and the second-order phase transitions 16 . Figure 2 c shows a modified Arrott plot 17 of the tricritical mean-field model for the FM order with β Arrott = 0.25 and γ Arrott = 1 in ( H/M ) 1/ γArrott and M 1/ βArrott , respectively. Compared to other magnetic ordering models, it is apparent from the relative slopes (dashed red lines in Fig. 2 c and Supplementary Fig. 2a–d) that the FM transition belongs to the universality class of the tricritical mean-field model (Fig. 2 d). A clear crossover from a first-order to second-order transition is seen in the T dependent ρ and M curves under different H as shown in Fig. 2 e,f, respectively. Three representative features in the data verify the crossover between FM orders: (i) disappearance of the peak in ρ at T C , (ii) suppression of the hysteresis in the ρ – T curve during a thermal cycle (insets of Fig. 2 e), and (iii) smooth increase of M upon cooling (Fig. 2 f). Such tricritical behaviour often emerges in heavy-fermion systems such as UGe 2 18 and YbRh 2 Si 2 19 due to the competition between Kondo coupling ( T K ) and Ruderman–Kittel–Kasuya–Yosida interaction 20 . Heavy-fermions with non-Fermi liquid behaviour. More unusual properties of Gd 3 SnC may be found in the heat capacity ( C ) measurement results (Fig. 3 ). As a way to determine the unexpected behaviour, we compare the C of Gd 3 SnC to those of FM Gd metal and non-magnetic La 3 SnC antiperovskite, as shown in Fig. 3 a. In contrast to the small C values of Gd metal and La 3 SnC antiperovskite in the low- T region, an extremely large C value with a Sommerfeld coefficient ( γ ) of ~ 1114 mJ mol − 1 K − 2 at 90 mK is observed for the Gd 3 SnC. The dramatic low- T rise of C is reminiscent of a nuclear Schottky anomaly, most likely from the Sn nucleus (the natural abundance for non-zero nuclear spin 13 C is below 1%). However, our modelling, which considers 16 % natural abundance of 117 Sn and 119 Sn, rules out the Schottky anomaly by showing that the required internal field is about − 1287 kOe, a value much larger than any reported values 21 – 23 (Supplementary Fig. 4d). In addition, the Gd nuclear spin cannot be the culprit as we do not see a similar rise in C for Gd metal. Therefore, we attribute the logarithmic rise of C for Gd 3 SnC below ~ 0.13 K (Supplementary Fig. 4a) to a non-Fermi-liquid (NFL) behaviour of itinerant conduction electrons 24 – 26 (inset of Fig. 3 a). A T -linear dependence of ρ in the low- T region also supports the NFL behaviour of itinerant conduction electrons in Gd 3 SnC (left panel in Fig. 3 b). The transition from T -linear to T 2 behaviour of ρ upon applying 140 kOe (right panel in Fig. 3 b and Supplementary Fig. 5) is suggestive of a magnetic origin of the NFL behaviour 27 , 28 . Thus, we assume that an exotic quantum phenomenon coupled with a correlation between itinerant and localized electrons in the Gd 3 SnC antiperovskite appears as heavy fermions. As Gd f-electron levels locate deep in the binding energy, the heavy-fermion with the NFL behaviour should originate from the electrons of other orbitals, which is revealed from the analysis of the C of FM Gd 3 SnC. The magnetic contribution ( C mag ) to the C of FM Gd 3 SnC is obtained by subtracting the C of non-magnetic La 3 SnC without 4f-electrons (La metal with the configuration of [Xe]4f 0 5d 1 6s 2 ) from those of Gd 3 SnC with seven 4f-electrons (Gd metal with the configuration of [Xe]4f 7 5d 1 6s 2 ). We find two distinct features in C mag : a large C mag in the high- T region ( C mag,high , Fig. 3 c) and a small C mag in the low- T region ( C mag, low , inset of Fig. 3 c). While the C mag,high is attributed to the FM order of 4f 7 -electrons, which agrees well with the prediction of the renormalization-group approach 29 in the scheme of tricritical ferromagnetism (Supplementary Fig. 2f), the origin of C mag,low is ambiguous. From the T -dependent magnetic entropy (Δ S ) obtained by integrating C mag ( T ) (Supplementary Fig. 4b), we can assign which electrons are responsible for C mag,low . Figure 3 d shows a large difference in Δ S between the high- and low- T regions: 0.5 R ln8 and 0.05 R ln2, respectively. Since 0.5 R ln8 reflects the contribution from seven 4f-electrons (4f 7 ) involved in FM ordering, one may notice that the much smaller value of 0.05 R ln2 has no correlation with 4f-electrons but is ascribed to 5d-electrons, which are responsible for the heavy-fermion with the NFL behaviour. Dual character of Gd 5d electrons. This unconventional and anomalous d-electron heavy-fermion state in f-block Gd-based Gd 3 SnC is, if true, the first case of FM-assisted heavy-fermion behaviour in 5d-electron systems. Density functional theory (DFT) calculations along with angle-resolved photoemission spectroscopy (ARPES) measurements provide a clear picture for the formation of the heavy-fermion state, which is induced not by 4f-electrons but by 5d-electrons of Gd element in the context of mixed bonding characters of the antiperovskite structure. Figure 4 a shows ARPES data along the Γ–X–Γ direction taken above (125 K) and below (90 and 13 K) the T C . The 125 K data shows a fast-dispersing band centred at the X point. As the T is lowered to 90 K, the band shifts down due to the exchange splitting of both 4f- and 5d-electrons (Supplementary Fig. 6d). In addition to the fast-dispersing band (green curve), there is a weakly dispersing band near E F (red curve in Fig. 4 a, Supplementary Fig. 6a–c). Upon cooling to 13 K, the fast-dispersing band shifts further down, and the weakly dispersing band near E F disappears. These changes in the electronic structure might be related to the hybridization of fast and weakly dispersing bands below 20 K. The T -dependent electronic structure change is also seen in the k x – k y plane of Fermi surface maps in Fig. 4 b; the Fermi surface pocket becomes larger as the T decreases. This enlarged Fermi surface is a typical phenomenon as found in various heavy-fermion systems 27,30−32 . The calculated partial density of states (DOS) clearly demonstrates that the Gd 5d-orbitals are almost solely responsible for the states near E F , while Sn 5p and C 2p derived states are located away from E F (Fig. 4 c). Meanwhile, we confirm that the contribution of Gd 4f-orbitals into the band structure near E F is negligible but responsible for the FM ordering (Supplementary Fig. 7). We note that the calculated band structure shows an anomalous flat band feature near E F , which is also a signature of heavy-fermion behaviour (Fig. 4 d,e). The experimentally observed flatness of the fast-dispersing band at the X point (13 K in Fig. 4 a) is indeed well-reproduced by band calculations (highlighted as yellow colour in Fig. 4 e). The fat band analysis reveals that the band hybridization triggers the appearance of a flat band feature near E F . Importantly, the two hybridized bands originate from the only Gd 5d-orbitals: t 2g bands from the Gd–Gd bonds (red curves) and e g bands from the mostly Gd–C bonds (green curves). Thus, we believe that the flat t 2g band observed at 90 K (Fig. 4 a) is lifted above E F after the band hybridization process (Supplementary Fig. 6e). Finally, we emphasize the importance of antiperovskite structure with mixed bonding nature, which is the key to imparting the unusual heavy-fermion behaviour to Gd 3 SnC. The crystal orbital Hamiltonian population (COHP) analysis (Fig. 4 f) explains how the chemical bonds of CGd 6 octahedra in antiperovskite structure can induce the unusual band structure. The COHP analysis suggests two types of orbital overlap: a small orbital overlap in metallic Gd–Gd bond responsible for the t 2g bands near E F (− ICOHP ~ 0.5 eV/bond, Supplementary Table 2) and large orbital overlap in covalent Gd–C bond for the e g bands below E F (− ICOHP ~ 1.5 eV/bond). This mixed bonding nature with the different degrees of orbital overlap leads to the unusual band dispersion of Gd 5d-electrons, as illustrated in Fig. 4 g − i. Thus, the duality of Gd 5d-electrons participating in the mixed chemical bonds in CGd 6 octahedra of the Gd 3 SnC antiperovskite structure is a key factor that determines the unusual physical properties. Summary In summary, we discovered the d-electron heavy-fermion state in the f-electron FM Gd 3 SnC antiperovskite. The mixed bonding nature of the antiperovskite structure, composed of metallic Gd–Gd bonds and covalent Gd–C bonds, is found to be the key ingredient for realizing the heavy-fermions of Gd 5d-electrons. The present findings are against the knowledge that the FM lanthanide elements are not suitable for heavy-fermion states, implying that the properties of the elements in the common crystal structure can be completely changed by adopting the antistructured lattice framework. This work will trigger further exploratory studies on the antistructures to challenge the common knowledge in the elemental properties of materials. Methods Crystal growth and structural analysis. Stoichiometric Polycrystalline Gd 3 SnC ingot rods were used for the single-crystal growth by the floating zone (FZ) melting method. We mixed Gd, Sn metals, and graphite chips in a 3:1:1 molar ration to fabricate a polycrystal ingot rod. The mixed sample was melted using the arc melting furnace in a high purity argon atmosphere (Ar > 99.9999%). The single crystal was grown by four-mirror FZ melting method with the rod-shaped ingots under high purity argon (Ar > 99.9999%) with pressurized conditions in 0.3 MPa. The feed and the seed rod were rotated at 50 rpm, and the growing speed was 2 mm per hour. The crystal structure was determined using the high-resolution X-ray diffractometer and Rietveld analysis using the GSAS-II program. Physical property measurements. ρ , M , and C measurements were performed using a physical property measurement system (PPMS). The ρ and C at ambient pressure were measured down to 0.06 K using a diluted helium-3 refrigerator. To measure the electrical properties of samples, the electrical contacts in the four-probe configuration were adopted that made by Ag epoxy onto a sample. To prevent movement of samples by H (up to 140 kOe) in the chamber, samples were fixed using torr seal epoxy onto the PPMS puck. To measure the M of the sample, a vibrating sample magnetometer (VSM) was used. For C measurement, the standard relaxation method was adopted. Every process was performed in an Ar-filled glove box, and N-grease covered samples for ρ and C measurements to prevent degradation of Gd 3 SnC under ambient oxygen and water vapour atmosphere. T -dependent ARPES measurements were performed at the MERLIN beamline 4.0.3 of the Advanced Light Source, Lawrence Berkeley National Laboratory using both linearly horizontal (π) and vertical (σ) polarization from an elliptically polarized undulator. Spectra were acquired with a Scienta R8000 (BL 4.0.3) electron analyser. Cleaving of the samples was conducted at 13 K in an ultra-high vacuum better than 5 × 10 − 11 Torr. The total energy resolution of approximately 15 meV was used for measurements at hν = 142 eV. DFT Calculations. First-principles DFT calculations were performed using the generalized gradient approximation with the Perder-Burke-Ernzerhof functional with spin-orbit coupling (SOC) and the projector augmented plane-wave method implemented in the Vienna ab initio simulation program code 33 – 35 . The 4f-, 5s-, 5p-, 5d- and 6s-electrons of Gd, the 5s- and 5p-electrons of Sn, and the 2s- and 2p-electrons of C were used as valence electrons. The plane-wave-basis cut-off energy was set to 600 eV. On-site Coulomb interaction values of U = 3 eV were used for the Gd 5d-electrons (Supplementary Fig. 7). Self-consistency was carried out using an a × b × c unit cell containing 5 atoms, and a 12 × 12 × 12 k -point mesh was used. Structural relaxation was performed until the Hellmann-Feynman forces were less than 1 × 10 − 5 eV Å −1 , respectively. The crystal structures and charge density distribution were visualized with the Visualization for Electronic and Structural Analysis code 36 . Declarations Data Availability The data that support the plots in this paper and other findings of this study are available from the corresponding author upon reasonable request. Acknowledgments This work was supported by the Institute for Basic Science (IBS-R011-D1, IBS-R009-G2) and the National Research Foundation of Korea (NRF) grant funded by the Korean government (Ministry of Science, ICT & Future Planning) (No. 2015M3D1A1070639, NRF-2019R1I1A1A01061913) and. We acknowledge Dr. Filip Ronning (Los Alamos National Laboratory) for valuable discussions. Author Contributions S.W.K. conceived the idea and organized the research. J.P. synthesized samples and measured physical properties. M.K and C.K. performed ARPES measurements. J.B, J.P, and K.L. analysed the structural and physical properties. J.B carried out computational studies. All the authors discussed the results and wrote the manuscript. Competing interests The authors declare no competing interests. Additional Information Supplementary information is available for this paper at https://doi.org/xxxxx. Correspondence and requests for materials should be addressed to S.W.K. Peer review information Nature Materials thanks XXXX and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Reprints and permission information is available at http://www.nature.com/reprints. Publisher’s note : Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rights and permissions Reprints and Permissions References Jeon, S. et al. Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd 3 As 2 . Nat. Mater. 13 , 851–856 (2014). Liu, Z. K. et al. A stable three-dimensional topological Dirac semimetal Cd 3 As 2 . Nat. Mater. 13 , 677–681 (2014). Neupane, M. et al. Observation of a three-dimensional topological Dirac semimetal phase in high-mobility Cd 3 As 2 . Nat. 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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-336915","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":17329739,"identity":"68b6ccf1-aeb5-4abc-a0f2-6a5b7148fce7","order_by":0,"name":"Joonho Bang","email":"","orcid":"https://orcid.org/0000-0002-9455-5378","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Joonho","middleName":"","lastName":"Bang","suffix":""},{"id":17329741,"identity":"bd4a9a4a-7ab5-4c13-8c5d-a6a0bf5b1aba","order_by":1,"name":"Jongho Park","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Jongho","middleName":"","lastName":"Park","suffix":""},{"id":17329743,"identity":"0f2368cf-f9a6-4ae6-8996-1c4a4a0a0ce9","order_by":2,"name":"Kimoon Lee","email":"","orcid":"","institution":"Kunsan National University","correspondingAuthor":false,"prefix":"","firstName":"Kimoon","middleName":"","lastName":"Lee","suffix":""},{"id":17329745,"identity":"1e569855-348b-445d-bcb7-0149c1ad334e","order_by":3,"name":"Minsoo Kim","email":"","orcid":"https://orcid.org/0000-0002-4137-4610","institution":"Center for Correlated Electron Systems, Institute for Basic Science","correspondingAuthor":false,"prefix":"","firstName":"Minsoo","middleName":"","lastName":"Kim","suffix":""},{"id":17329746,"identity":"b0a18b0e-5502-4b73-a412-7120452f548d","order_by":4,"name":"Wonshik Kyung","email":"","orcid":"https://orcid.org/0000-0001-8750-5471","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Wonshik","middleName":"","lastName":"Kyung","suffix":""},{"id":17329748,"identity":"81352cc7-29f2-4640-8ac7-14495895e4f7","order_by":5,"name":"Jonathan Denlinger","email":"","orcid":"https://orcid.org/0000-0001-7645-1631","institution":"Lawrence Berkeley National Lab","correspondingAuthor":false,"prefix":"","firstName":"Jonathan","middleName":"","lastName":"Denlinger","suffix":""},{"id":17329750,"identity":"30dbaab6-7014-4954-a2a2-f3bd6e7ae365","order_by":6,"name":"Yeong Kwan Kim","email":"","orcid":"","institution":"Korea Advanced Institute of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yeong","middleName":"Kwan","lastName":"Kim","suffix":""},{"id":17329751,"identity":"d120f0ec-557b-4321-88db-3690c5bfcfc7","order_by":7,"name":"Young Hee Lee","email":"","orcid":"https://orcid.org/0000-0001-7403-8157","institution":"Institute for Basic Science","correspondingAuthor":false,"prefix":"","firstName":"Young","middleName":"Hee","lastName":"Lee","suffix":""},{"id":17329752,"identity":"0798830d-636f-4da7-a8e7-d347cb117857","order_by":8,"name":"Changyoung Kim","email":"","orcid":"https://orcid.org/0000-0003-0555-2341","institution":"Seoul National University","correspondingAuthor":false,"prefix":"","firstName":"Changyoung","middleName":"","lastName":"Kim","suffix":""},{"id":17329753,"identity":"56da6df5-cf43-46a2-9c91-5dcbaebc8cc2","order_by":9,"name":"Sung Wng Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4klEQVRIiWNgGAWjYBACCWY4k/kAY8MBECOBaC1sCURqQTB5DIjTItnOnfyZd0dt4nb+NZ8/zjhzmIGfPccArxZpZt5t0rxnjifunPF2m+SGG4cZJHve4NciB9TCzNt2LHfDjbPbGB98OMxgcIOALUAtmz9DtJx5/BGkxZ6QFqDDNkjzttXkbjjfwwB2mIEEAS2SzbzbJOe2HajfcIPNTHLGmXQeiTPPCvBqkTh/dvOHt211xgbnDz/+2HPMWo6/PXkDXi1QcBioOQHM4iFGOQjUMTDwHyBW8SgYBaNgFIw0AACGjFD+8P+rhwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-4802-5421","institution":"Sungkyunkwan University","correspondingAuthor":true,"prefix":"","firstName":"Sung","middleName":"Wng","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2021-03-17 07:15:47","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-336915/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-336915/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":7350145,"identity":"c2897c2d-5a33-4d0a-8b80-bcec392090b5","added_by":"auto","created_at":"2021-03-25 13:56:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":209638,"visible":true,"origin":"","legend":"Crystal structure and mixed bonding nature of Gd3SnC antiperovskite. a, Powder XRD pattern with Rietveld fitting of Gd3SnC. The measurement was performed at room temperature. The inset depicts the crystal structure obtained from the Rietveld refinement result. b, Comparison of bonding features in Gd-based compounds. Red, green, and brown colours represent the metallic Gd–Gd (M–M), covalent Gd–ligand (M–L), and ionic Gd–ligand (M–L) bonds, respectively. The bond length of Gd–Gd and Gd–C bonds, and electronegativity difference (Δelectronegativity) between Gd and surrounding ligands are also shown in the crystal structures. Schematics of molecular orbital diagrams are shown in the lower panel. (M–L)* represents the antibonding molecular orbital of M–L bonds.","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-336915/v1/43beb136d2efc65bfb5cd249.png"},{"id":7349999,"identity":"ebb214a1-ae54-47f3-a6b1-6ec313174f21","added_by":"auto","created_at":"2021-03-25 13:54:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":264724,"visible":true,"origin":"","legend":"Tricritical ferromagnetic behaviour in Gd3SnC antiperovskite. a, T-dependent M under zero-field cooling (ZFC) and field cooling (FC) conditions. Inverse magnetization (M−1) for FC result is also illustrated. The inset shows an enlarged view of the ZFC curve at low T. Dashed black line is a guide for the eyes. b, H-dependent effective magnetic moment (µeff) per Gd atom at various T. μeff–H curve for Gd metal obtained at 2 K is also shown as a reference (dashed black curve). c, Modified Arrott plot for the tricritical mean-field model. Modified Arrott plots for other models are presented in Supplementary Fig. 2a–d. The dashed red lines are linear fits for the high field regime. d, T-dependent relative slope (RS) curves near the TC for various models. e, Cooling and heating curves of T-dependent ρ for various H values. f, M–T curves for various H values.","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-336915/v1/349f11b4584dae50c2ff2e6a.png"},{"id":7350146,"identity":"70d3712f-a222-4887-9a5c-d7999c4bc952","added_by":"auto","created_at":"2021-03-25 13:57:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":178583,"visible":true,"origin":"","legend":"Unconventional heavy-fermion behaviour with non-Fermi-liquid behaviour in Gd3SnC antiperovskite. a, C/T versus T2 curves for antiperovskite Gd3SnC, isostructural La3SnC, and Gd metal. The C value of Gd3SnC corresponds to the heat capacity per mole of Gd. The inset shows a fitting result of C versus T curve of Gd3SnC using CNFL = −AlnT + B and Cel+ph = CT + DT 3, where CNFL and Cel+ph are NFL and electron + phonon contributions, respectively. A, B, C, and D are constants. b, T dependent ρ at different H. Red curves are single power-law fits (ρ = ρ0 + ATn) of the data. c, C versus T for Gd3SnC and La3SnC. The inset is an enlarged view of the low-T region. Cmag for Gd3SnC is estimated by subtracting the C of the non-magnetic La3SnC (Supplementary Fig. 4b). d, T-dependent ΔS − ΔS0 for Gd3SnC per mole of Gd. ΔS0 is the residual entropy. The red curve represents the FM contribution obeying ΔS − ΔS0 = ∫ (aT 3/2 + b)/T dT, where a and b are constants. The inset shows a magnified view below 40 K.","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-336915/v1/aea71c952eb15e6060c50431.png"},{"id":7350285,"identity":"d4e7da04-1841-4951-8af9-a7e905618902","added_by":"auto","created_at":"2021-03-25 14:00:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":778973,"visible":true,"origin":"","legend":"Electronic structure of heavy-fermion Gd3SnC antiperovskite. a, ARPES spectra along the Γ–X–Γ direction at 125, 90, and 13 K. Green and red solid curves indicate fast-dispersing band and weakly dispersing band, respectively. Details on the energy distribution curves (EDCs) are shown in Supplementary Fig. 6. b, Fermi surface topology in the kx–ky plane from ARPES measurements at 125 and 13 K. White and black squares represent the first Brillouin zone. c, Calculated partial DOS. d, Calculated band structure along the Γ–X–Γ direction with fat band analysis, exhibiting the t2g (red colour) and eg (green colour) contributions of Gd 5d-orbitals. Band thickness represents the contribution of each orbital. e, Near Fermi energy band structure around the X point, showing a band hybridization between fast-dispersing and weakly dispersing bands. f, Partial COHP (pCOHP) for Gd–Gd, Gd–C, and Gd–Sn bonds. pCOHP for other bonds can be found in Supplementary Fig. 8. g–i, Schematic illustration of the mixed bonding state for Gd 5d-orbitals.","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-336915/v1/165d56e7c39aa65526131b53.png"},{"id":15672571,"identity":"af9a6f4c-6082-4389-8ebf-4f71a7168e96","added_by":"auto","created_at":"2021-11-18 14:12:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1896140,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-336915/v1/3e14f5b4-9d82-4d75-8362-ff309aba15f5.pdf"},{"id":7350148,"identity":"f9e57af9-3069-434a-a01d-86131873b140","added_by":"auto","created_at":"2021-03-25 13:57:00","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2066818,"visible":true,"origin":"","legend":"","description":"","filename":"20210317Gd3SnCSupplementary.docx","url":"https://assets-eu.researchsquare.com/files/rs-336915/v1/15bba6bb2f55477fb40f2334.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Unusual d-electron heavy-fermion behaviour in f-electron ferromagnetic antiperovskite Gd\u003csub\u003e3\u003c/sub\u003eSnC","fulltext":[{"header":"Introduction","content":" \u003cp\u003eThe crystal structure constructed with chemical bonds of constituent elements determines the electronic structure of a material and its properties. In a fixed symmetry, electronically inverted structures with switched crystallographic positions of cations and anions from the original structure often have a reversed compositional ratio, which necessarily forms a different coordinated substructure with additional bonding characters and can lead to an exotic electronic structure. However, in general, such antistructures composed of the same constituent elements in the reversed compositional ratio are thermodynamically unstable. Indeed, due to the thermodynamic constraints, antistructures found in several classes of materials are constructed by subsidiary chemical bonds of different constituent elements from original structures. This appears, for example, in the Cd-deficient Cd\u003csub\u003e3\u003c/sub\u003eAs\u003csub\u003e2\u003c/sub\u003e antifluorite\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, which has a strong covalent bonding nature in a reversed compositional ratio from the ionic CaF\u003csub\u003e2\u003c/sub\u003e fluorite. It is noteworthy that the Cd\u003csub\u003e3\u003c/sub\u003eAs\u003csub\u003e2\u003c/sub\u003e antifluorite exhibits exotic properties: a three-dimensional topological Dirac band\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e along with negative magnetoresistance\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, anomalous Hall effect\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, and pressure-induced superconductivity\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cem\u003eABX\u003c/em\u003e \u003csub\u003e3\u003c/sub\u003e perovskites, as the largest family of crystalline materials, also have their counterpart antistructures, \u003cem\u003eA\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e\u003cem\u003eBX\u003c/em\u003e antiperovskites\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. In contrast to the perovskite compounds constructed by the ionic bonds of constituent elements in stable valence states, the antiperovskites have mixed bonding characters with ionic, covalent, and metallic bonds in unusual valence states\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. However, oxide antiperovskites (\u003cem\u003eA\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e\u003cem\u003eB\u003c/em\u003eO), antistructures of common oxide perovskites (\u003cem\u003eAB\u003c/em\u003eO\u003csub\u003e3\u003c/sub\u003e), are hardly stabilized in ambient conditions as oxygen tends to form ionic bonds with counter-cationic \u003cem\u003eA\u003c/em\u003e and \u003cem\u003eB\u003c/em\u003e elements due to its large ionicity\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. This constraint may be lifted for s-block and transition metal-based antiperovskites, in which additional covalent and metallic bonds come into play for their crystallographic stability\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. The boundary for such stable antiperovskite compounds can be extended to f-block lanthanides, which form a crystal with various elemental groups of d-block transition metals and p-block post-transition metals\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Those compounds may exhibit diverse electronic properties because of the multiple bonding characters with enhanced covalency and/or metallicity. Furthermore, considering the fact that f-electrons often contribute to strongly correlated electronic properties, a variety of unconventional quantum phenomena may be anticipated in f-block antiperovskites, which can exhibit exotic electronic band structures arising from the mixed chemical bonds. However, thermodynamically stable f-block element-based antiperovskites and their novel properties have been hardly demonstrated up to now\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Herein, we demonstrate the unprecedented heavy-fermion behaviour of the ferromagnetic (FM) gadolinium lattice in the Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite structure and verify the crucial role of the metallic Gd\u0026ndash;Gd and covalent Gd\u0026ndash;C bonds of CGd\u003csub\u003e6\u003c/sub\u003e octahedral skeleton on an unusually hybridized Gd 5d-electrons responsible for the emergent heavy-fermions.\u003c/p\u003e "},{"header":"Results","content":" \u003cp\u003e \u003cb\u003eSynthesis and structural analysis.\u003c/b\u003e Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows that the Gd\u003csub\u003e3\u003c/sub\u003eSnC crystallizes in the antiperovskite structure (space group: \u003cem\u003ePm\u003c/em\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\stackrel{-}{3}\\)\u003c/span\u003e\u003c/span\u003e\u003cem\u003em\u003c/em\u003e) with face-centred Gd and body-centred C atoms in a Sn cubic lattice, as confirmed by Rietveld analysis of powder X-ray diffraction (XRD) pattern (Supplementary Table\u0026nbsp;1). Single-phase bulk Gd\u003csub\u003e3\u003c/sub\u003eSnC was synthesized via the melt-solidification process at one atmosphere. This indicates the thermodynamic stability of Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite, which gets additional support from the calculated phonon dispersions having no imaginary frequency (Supplementary Fig.\u0026nbsp;1). In contrast to the \u003cem\u003eABX\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e perovskite, which has cation-centred \u003cem\u003eBX\u003c/em\u003e\u003csub\u003e6\u003c/sub\u003e octahedra with ionic bonds, Gd\u003csub\u003e3\u003c/sub\u003eSnC has anion-centred CGd\u003csub\u003e6\u003c/sub\u003e octahedra with strong covalent Gd\u0026ndash;C and metallic Gd\u0026ndash;Gd bonds. This mixed bonding character of Gd bonds in CGd\u003csub\u003e6\u003c/sub\u003e octahedra results in different Gd orbital levels from those of the Gd element and its ionic compounds. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, while Gd metal and Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e have ordinary Gd orbital levels of Gd\u0026ndash;Gd metallic and Gd\u0026ndash;O ionic bonds, respectively, Gd\u003csub\u003e3\u003c/sub\u003eSnC has unusual energy levels for Gd orbitals due to the coexistence of metallic and covalent bonds. Considering the shorter Gd\u0026ndash;Gd bond length (3.48 \u0026Aring;) in CGd\u003csub\u003e6\u003c/sub\u003e octahedra compared to that of Gd metal (~\u0026thinsp;3.6 \u0026Aring;), one expects an enhanced metallicity and thus additional Fermi level (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e) crossings for Gd bands in Gd\u003csub\u003e3\u003c/sub\u003eSnC. On the other hand, the electronegativity difference between Gd and C is much smaller than that between Gd and O, resulting in the formation of covalent bonds between Gd and C. The energy difference between bonding and antibonding states of the covalent bonds is expected to be significantly smaller than that of ionic bonds between Gd and O. These mixed bonding characters of Gd valence orbitals in CGd\u003csub\u003e6\u003c/sub\u003e octahedra can lead to a peculiar molecular orbital diagram with both metallic and covalent bonds as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. Such observation indicates that Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite may exhibit unusual physical properties that are hardly found in elemental Gd and conventional Gd-related compounds.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eTricritical ferromagnetic behaviour.\u003c/b\u003e Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the FM phase transition of Gd\u003csub\u003e3\u003c/sub\u003eSnC with a Curie temperature (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e) of 100 K under a low magnetic field (\u003cem\u003eH\u003c/em\u003e) of 0.1 kOe. In comparison to the itinerant FM in Gd metal with a \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of 297 K, different aspects of the FM order are observed\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. A sharp increase in the magnetization (\u003cem\u003eM\u003c/em\u003e) near the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e indicates a first-order transition, which is further evidenced by the hysteresis in the temperature(\u003cem\u003eT\u003c/em\u003e) dependence of electrical resistivity (\u003cem\u003eρ\u003c/em\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee) and the negative slope in the \u003cem\u003eM\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e dependence of \u003cem\u003eH\u003c/em\u003e/\u003cem\u003eM\u003c/em\u003e (Supplementary Fig.\u0026nbsp;2e). In addition, no structural phase transition is observed around the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, indicating that the FM ordering occurs while preserving the antiperovskite structure (Supplementary Fig.\u0026nbsp;3). We confirm the saturation magnetic moment of \u0026sim;6.8 \u003cem\u003e\u0026micro;\u003c/em\u003e\u003csub\u003eB\u003c/sub\u003e per Gd obtained from the \u003cem\u003eM\u003c/em\u003e\u0026ndash;\u003cem\u003eH\u003c/em\u003e curve (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), indicating this FM state comes mostly from the seven Gd 4f-electrons. A notable aspect of \u003cem\u003eM\u003c/em\u003e (\u003cem\u003eT\u003c/em\u003e) is a slight decrease in the ZFC curve below ~\u0026thinsp;20 K (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), which suggests a possible formation of singlets such as Kondo singlet\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, as will be discussed in the following sections. This unusual behaviour in \u003cem\u003eM\u003c/em\u003e indicates that the near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e states of Gd, which do not have contributions from fully localized f-orbitals, may be different from those of the familiar FM Gd metal and Gd-based compounds\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe most peculiar aspect of the FM state in Gd\u003csub\u003e3\u003c/sub\u003eSnC is the tricritical behaviour that appears near the boundary between the first- and the second-order phase transitions\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec shows a modified Arrott plot\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e of the tricritical mean-field model for the FM order with \u003cem\u003eβ\u003c/em\u003e\u003csub\u003eArrott\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.25 and \u003cem\u003eγ\u003c/em\u003e\u003csub\u003eArrott\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1 in (\u003cem\u003eH/M\u003c/em\u003e)\u003csup\u003e1/\u003cem\u003eγArrott\u003c/em\u003e\u003c/sup\u003e and \u003cem\u003eM\u003c/em\u003e\u003csup\u003e1/\u003cem\u003eβArrott\u003c/em\u003e\u003c/sup\u003e, respectively. Compared to other magnetic ordering models, it is apparent from the relative slopes (dashed red lines in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;2a\u0026ndash;d) that the FM transition belongs to the universality class of the tricritical mean-field model (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). A clear crossover from a first-order to second-order transition is seen in the \u003cem\u003eT\u003c/em\u003e dependent \u003cem\u003eρ\u003c/em\u003e and \u003cem\u003eM\u003c/em\u003e curves under different \u003cem\u003eH\u003c/em\u003e as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee,f, respectively. Three representative features in the data verify the crossover between FM orders: (i) disappearance of the peak in \u003cem\u003eρ\u003c/em\u003e at \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, (ii) suppression of the hysteresis in the \u003cem\u003eρ\u003c/em\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e curve during a thermal cycle (insets of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), and (iii) smooth increase of \u003cem\u003eM\u003c/em\u003e upon cooling (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). Such tricritical behaviour often emerges in heavy-fermion systems such as UGe\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e18\u003c/sup\u003e and YbRh\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e19\u003c/sup\u003e due to the competition between Kondo coupling (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eK\u003c/sub\u003e) and Ruderman\u0026ndash;Kittel\u0026ndash;Kasuya\u0026ndash;Yosida interaction\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cb\u003eHeavy-fermions with non-Fermi liquid behaviour.\u003c/b\u003e More unusual properties of Gd\u003csub\u003e3\u003c/sub\u003eSnC may be found in the heat capacity (\u003cem\u003eC\u003c/em\u003e) measurement results (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). As a way to determine the unexpected behaviour, we compare the \u003cem\u003eC\u003c/em\u003e of Gd\u003csub\u003e3\u003c/sub\u003eSnC to those of FM Gd metal and non-magnetic La\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. In contrast to the small \u003cem\u003eC\u003c/em\u003e values of Gd metal and La\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite in the low-\u003cem\u003eT\u003c/em\u003e region, an extremely large \u003cem\u003eC\u003c/em\u003e value with a Sommerfeld coefficient (\u003cem\u003eγ\u003c/em\u003e) of ~\u0026thinsp;1114 mJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 90 mK is observed for the Gd\u003csub\u003e3\u003c/sub\u003eSnC. The dramatic low-\u003cem\u003eT\u003c/em\u003e rise of \u003cem\u003eC\u003c/em\u003e is reminiscent of a nuclear Schottky anomaly, most likely from the Sn nucleus (the natural abundance for non-zero nuclear spin \u003csup\u003e13\u003c/sup\u003eC is below 1%). However, our modelling, which considers 16 % natural abundance of \u003csup\u003e117\u003c/sup\u003eSn and \u003csup\u003e119\u003c/sup\u003eSn, rules out the Schottky anomaly by showing that the required internal field is about \u0026minus;\u0026thinsp;1287 kOe, a value much larger than any reported values\u003csup\u003e\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;4d). In addition, the Gd nuclear spin cannot be the culprit as we do not see a similar rise in \u003cem\u003eC\u003c/em\u003e for Gd metal. Therefore, we attribute the logarithmic rise of \u003cem\u003eC\u003c/em\u003e for Gd\u003csub\u003e3\u003c/sub\u003eSnC below ~\u0026thinsp;0.13 K (Supplementary Fig.\u0026nbsp;4a) to a non-Fermi-liquid (NFL) behaviour of itinerant conduction electrons\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). A \u003cem\u003eT\u003c/em\u003e-linear dependence of \u003cem\u003eρ\u003c/em\u003e in the low-\u003cem\u003eT\u003c/em\u003e region also supports the NFL behaviour of itinerant conduction electrons in Gd\u003csub\u003e3\u003c/sub\u003eSnC (left panel in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The transition from \u003cem\u003eT\u003c/em\u003e-linear to \u003cem\u003eT\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e behaviour of \u003cem\u003eρ\u003c/em\u003e upon applying 140 kOe (right panel in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;5) is suggestive of a magnetic origin of the NFL behaviour\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Thus, we assume that an exotic quantum phenomenon coupled with a correlation between itinerant and localized electrons in the Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite appears as heavy fermions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs Gd f-electron levels locate deep in the binding energy, the heavy-fermion with the NFL behaviour should originate from the electrons of other orbitals, which is revealed from the analysis of the \u003cem\u003eC\u003c/em\u003e of FM Gd\u003csub\u003e3\u003c/sub\u003eSnC. The magnetic contribution (\u003cem\u003eC\u003c/em\u003e\u003csub\u003emag\u003c/sub\u003e) to the \u003cem\u003eC\u003c/em\u003e of FM Gd\u003csub\u003e3\u003c/sub\u003eSnC is obtained by subtracting the \u003cem\u003eC\u003c/em\u003e of non-magnetic La\u003csub\u003e3\u003c/sub\u003eSnC without 4f-electrons (La metal with the configuration of [Xe]4f\u003csup\u003e0\u003c/sup\u003e5d\u003csup\u003e1\u003c/sup\u003e6s\u003csup\u003e2\u003c/sup\u003e) from those of Gd\u003csub\u003e3\u003c/sub\u003eSnC with seven 4f-electrons (Gd metal with the configuration of [Xe]4f\u003csup\u003e7\u003c/sup\u003e5d\u003csup\u003e1\u003c/sup\u003e6s\u003csup\u003e2\u003c/sup\u003e). We find two distinct features in \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag\u003c/sub\u003e: a large \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag\u003c/sub\u003e in the high-\u003cem\u003eT\u003c/em\u003e region (\u003cem\u003eC\u003c/em\u003e\u003csub\u003emag,high\u003c/sub\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec) and a small \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag\u003c/sub\u003e in the low-\u003cem\u003eT\u003c/em\u003e region (\u003cem\u003eC\u003c/em\u003e\u003csub\u003emag, low\u003c/sub\u003e, inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). While the \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag,high\u003c/sub\u003e is attributed to the FM order of 4f\u003csup\u003e7\u003c/sup\u003e-electrons, which agrees well with the prediction of the renormalization-group approach\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e in the scheme of tricritical ferromagnetism (Supplementary Fig.\u0026nbsp;2f), the origin of \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag,low\u003c/sub\u003e is ambiguous. From the \u003cem\u003eT\u003c/em\u003e-dependent magnetic entropy (Δ\u003cem\u003eS\u003c/em\u003e) obtained by integrating \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag\u003c/sub\u003e (\u003cem\u003eT\u003c/em\u003e) (Supplementary Fig.\u0026nbsp;4b), we can assign which electrons are responsible for \u003cem\u003eC\u003c/em\u003e\u003csub\u003emag,low\u003c/sub\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed shows a large difference in Δ\u003cem\u003eS\u003c/em\u003e between the high- and low-\u003cem\u003eT\u003c/em\u003e regions: 0.5\u003cem\u003eR\u003c/em\u003eln8 and 0.05\u003cem\u003eR\u003c/em\u003eln2, respectively. Since 0.5\u003cem\u003eR\u003c/em\u003eln8 reflects the contribution from seven 4f-electrons (4f\u003csup\u003e7\u003c/sup\u003e) involved in FM ordering, one may notice that the much smaller value of 0.05\u003cem\u003eR\u003c/em\u003eln2 has no correlation with 4f-electrons but is ascribed to 5d-electrons, which are responsible for the heavy-fermion with the NFL behaviour.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDual character of Gd 5d electrons.\u003c/b\u003e This unconventional and anomalous d-electron heavy-fermion state in f-block Gd-based Gd\u003csub\u003e3\u003c/sub\u003eSnC is, if true, the first case of FM-assisted heavy-fermion behaviour in 5d-electron systems. Density functional theory (DFT) calculations along with angle-resolved photoemission spectroscopy (ARPES) measurements provide a clear picture for the formation of the heavy-fermion state, which is induced not by 4f-electrons but by 5d-electrons of Gd element in the context of mixed bonding characters of the antiperovskite structure. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea shows ARPES data along the Γ\u0026ndash;X\u0026ndash;Γ direction taken above (125 K) and below (90 and 13 K) the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e. The 125 K data shows a fast-dispersing band centred at the X point. As the \u003cem\u003eT\u003c/em\u003e is lowered to 90 K, the band shifts down due to the exchange splitting of both 4f- and 5d-electrons (Supplementary Fig.\u0026nbsp;6d). In addition to the fast-dispersing band (green curve), there is a weakly dispersing band near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e (red curve in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, Supplementary Fig.\u0026nbsp;6a\u0026ndash;c). Upon cooling to 13 K, the fast-dispersing band shifts further down, and the weakly dispersing band near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e disappears. These changes in the electronic structure might be related to the hybridization of fast and weakly dispersing bands below 20 K. The \u003cem\u003eT\u003c/em\u003e-dependent electronic structure change is also seen in the \u003cem\u003ek\u003c/em\u003e\u003csub\u003ex\u003c/sub\u003e\u0026ndash;\u003cem\u003ek\u003c/em\u003e\u003csub\u003ey\u003c/sub\u003e plane of Fermi surface maps in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb; the Fermi surface pocket becomes larger as the \u003cem\u003eT\u003c/em\u003e decreases. This enlarged Fermi surface is a typical phenomenon as found in various heavy-fermion systems\u003csup\u003e27,30\u0026minus;32\u003c/sup\u003e. The calculated partial density of states (DOS) clearly demonstrates that the Gd 5d-orbitals are almost solely responsible for the states near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e, while Sn 5p and C 2p derived states are located away from \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). Meanwhile, we confirm that the contribution of Gd 4f-orbitals into the band structure near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e is negligible but responsible for the FM ordering (Supplementary Fig.\u0026nbsp;7).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe note that the calculated band structure shows an anomalous flat band feature near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e, which is also a signature of heavy-fermion behaviour (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed,e). The experimentally observed flatness of the fast-dispersing band at the X point (13 K in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea) is indeed well-reproduced by band calculations (highlighted as yellow colour in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). The fat band analysis reveals that the band hybridization triggers the appearance of a flat band feature near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e. Importantly, the two hybridized bands originate from the only Gd 5d-orbitals: \u003cem\u003et\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e bands from the Gd\u0026ndash;Gd bonds (red curves) and \u003cem\u003ee\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e bands from the mostly Gd\u0026ndash;C bonds (green curves). Thus, we believe that the flat \u003cem\u003et\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e band observed at 90 K (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea) is lifted above \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e after the band hybridization process (Supplementary Fig.\u0026nbsp;6e). Finally, we emphasize the importance of antiperovskite structure with mixed bonding nature, which is the key to imparting the unusual heavy-fermion behaviour to Gd\u003csub\u003e3\u003c/sub\u003eSnC. The crystal orbital Hamiltonian population (COHP) analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef) explains how the chemical bonds of CGd\u003csub\u003e6\u003c/sub\u003e octahedra in antiperovskite structure can induce the unusual band structure. The COHP analysis suggests two types of orbital overlap: a small orbital overlap in metallic Gd\u0026ndash;Gd bond responsible for the \u003cem\u003et\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e bands near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e (\u0026minus;\u0026thinsp;ICOHP\u0026thinsp;~\u0026thinsp;0.5 eV/bond, Supplementary Table\u0026nbsp;2) and large orbital overlap in covalent Gd\u0026ndash;C bond for the \u003cem\u003ee\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e bands below \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e (\u0026minus;\u0026thinsp;ICOHP\u0026thinsp;~\u0026thinsp;1.5 eV/bond). This mixed bonding nature with the different degrees of orbital overlap leads to the unusual band dispersion of Gd 5d-electrons, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg\u0026thinsp;\u0026minus;\u0026thinsp;i. Thus, the duality of Gd 5d-electrons participating in the mixed chemical bonds in CGd\u003csub\u003e6\u003c/sub\u003e octahedra of the Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite structure is a key factor that determines the unusual physical properties.\u003c/p\u003e "},{"header":"Summary","content":" \u003cp\u003eIn summary, we discovered the d-electron heavy-fermion state in the f-electron FM Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite. The mixed bonding nature of the antiperovskite structure, composed of metallic Gd\u0026ndash;Gd bonds and covalent Gd\u0026ndash;C bonds, is found to be the key ingredient for realizing the heavy-fermions of Gd 5d-electrons. The present findings are against the knowledge that the FM lanthanide elements are not suitable for heavy-fermion states, implying that the properties of the elements in the common crystal structure can be completely changed by adopting the antistructured lattice framework. This work will trigger further exploratory studies on the antistructures to challenge the common knowledge in the elemental properties of materials.\u003c/p\u003e "},{"header":"Methods","content":" \u003cp\u003e \u003cb\u003eCrystal growth and structural analysis.\u003c/b\u003e Stoichiometric Polycrystalline Gd\u003csub\u003e3\u003c/sub\u003eSnC ingot rods were used for the single-crystal growth by the floating zone (FZ) melting method. We mixed Gd, Sn metals, and graphite chips in a 3:1:1 molar ration to fabricate a polycrystal ingot rod. The mixed sample was melted using the arc melting furnace in a high purity argon atmosphere (Ar\u0026thinsp;\u0026gt;\u0026thinsp;99.9999%). The single crystal was grown by four-mirror FZ melting method with the rod-shaped ingots under high purity argon (Ar\u0026thinsp;\u0026gt;\u0026thinsp;99.9999%) with pressurized conditions in 0.3 MPa. The feed and the seed rod were rotated at 50 rpm, and the growing speed was 2 mm per hour. The crystal structure was determined using the high-resolution X-ray diffractometer and Rietveld analysis using the GSAS-II program.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePhysical property measurements.\u003c/b\u003e \u003cem\u003eρ\u003c/em\u003e, \u003cem\u003eM\u003c/em\u003e, and \u003cem\u003eC\u003c/em\u003e measurements were performed using a physical property measurement system (PPMS). The \u003cem\u003eρ\u003c/em\u003e and \u003cem\u003eC\u003c/em\u003e at ambient pressure were measured down to 0.06 K using a diluted helium-3 refrigerator. To measure the electrical properties of samples, the electrical contacts in the four-probe configuration were adopted that made by Ag epoxy onto a sample. To prevent movement of samples by \u003cem\u003eH\u003c/em\u003e (up to 140 kOe) in the chamber, samples were fixed using torr seal epoxy onto the PPMS puck. To measure the \u003cem\u003eM\u003c/em\u003e of the sample, a vibrating sample magnetometer (VSM) was used. For \u003cem\u003eC\u003c/em\u003e measurement, the standard relaxation method was adopted. Every process was performed in an Ar-filled glove box, and N-grease covered samples for \u003cem\u003eρ\u003c/em\u003e and \u003cem\u003eC\u003c/em\u003e measurements to prevent degradation of Gd\u003csub\u003e3\u003c/sub\u003eSnC under ambient oxygen and water vapour atmosphere. \u003cem\u003eT\u003c/em\u003e-dependent ARPES measurements were performed at the MERLIN beamline 4.0.3 of the Advanced Light Source, Lawrence Berkeley National Laboratory using both linearly horizontal (π) and vertical (σ) polarization from an elliptically polarized undulator. Spectra were acquired with a Scienta R8000 (BL 4.0.3) electron analyser. Cleaving of the samples was conducted at 13 K in an ultra-high vacuum better than 5 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;11\u003c/sup\u003e Torr. The total energy resolution of approximately 15 meV was used for measurements at \u003cem\u003ehν\u003c/em\u003e\u0026thinsp;=\u0026thinsp;142 eV.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDFT Calculations.\u003c/b\u003e First-principles DFT calculations were performed using the generalized gradient approximation with the Perder-Burke-Ernzerhof functional with spin-orbit coupling (SOC) and the projector augmented plane-wave method implemented in the Vienna \u003cem\u003eab initio\u003c/em\u003e simulation program code\u003csup\u003e\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. The 4f-, 5s-, 5p-, 5d- and 6s-electrons of Gd, the 5s- and 5p-electrons of Sn, and the 2s- and 2p-electrons of C were used as valence electrons. The plane-wave-basis cut-off energy was set to 600 eV. On-site Coulomb interaction values of \u003cem\u003eU\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3 eV were used for the Gd 5d-electrons (Supplementary Fig.\u0026nbsp;7). Self-consistency was carried out using an \u003cem\u003ea\u003c/em\u003e \u0026times; \u003cem\u003eb\u003c/em\u003e \u0026times; \u003cem\u003ec\u003c/em\u003e unit cell containing 5 atoms, and a 12 \u0026times; 12 \u0026times; 12 \u003cem\u003ek\u003c/em\u003e-point mesh was used. Structural relaxation was performed until the Hellmann-Feynman forces were less than 1 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e eV \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. The crystal structures and charge density distribution were visualized with the Visualization for Electronic and Structural Analysis code\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the plots in this paper and other findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Institute for Basic Science (IBS-R011-D1, IBS-R009-G2) and the National Research Foundation of Korea (NRF) grant funded by the Korean government (Ministry of Science, ICT \u0026amp; Future Planning) (No. 2015M3D1A1070639, NRF-2019R1I1A1A01061913) and. We acknowledge Dr. Filip Ronning (Los Alamos National Laboratory) for valuable discussions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eS.W.K. conceived the idea and organized the research. J.P. synthesized samples and measured physical properties. M.K and C.K. performed ARPES measurements. J.B, J.P, and K.L. analysed the structural and physical properties. J.B carried out computational studies. All the authors discussed the results and wrote the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u003c/strong\u003e is available for this paper at https://doi.org/xxxxx.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence\u003c/strong\u003e and requests for materials should be addressed to S.W.K.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePeer review information \u003c/strong\u003e\u003cem\u003eNature Materials \u003c/em\u003ethanks XXXX and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReprints and permission information\u003c/strong\u003e is available at http://www.nature.com/reprints.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePublisher\u0026rsquo;s note\u003c/strong\u003e: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRights and permissions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eReprints and Permissions\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJeon, S. \u003cem\u003eet al.\u003c/em\u003e Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd\u003csub\u003e3\u003c/sub\u003eAs\u003csub\u003e2\u003c/sub\u003e. \u003cem\u003eNat. 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Crystallogr.\u003c/em\u003e \u003cb\u003e44\u003c/b\u003e, 1272\u0026ndash;1276 (2011).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"stable antistructures, heavy-fermion behaviour, ferromagnetic gadolinium lattice, Gd3SnC antiperovskite","lastPublishedDoi":"10.21203/rs.3.rs-336915/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-336915/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInverted structures of common crystal lattices, referred to as antistructures, are rare in nature due to their thermodynamic constraints imposed by the switched cation and anion positions in reference to the original structure. However, a stable antistructure formed with mixed bonding characters of constituent elements in unusual valence states can provide unexpected material properties. Here, we report a heavy-fermion behaviour of ferromagnetic gadolinium lattice in Gd\u003csub\u003e3\u003c/sub\u003eSnC antiperovskite, contradicting the common belief that ferromagnetic gadolinium cannot be a heavy-fermion system. The specific heat shows an unusually large Sommerfeld coefficient of ~\u0026thinsp;1114 mJ\u0026sdot;mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026sdot;K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with a logarithmic behaviour of non-Fermi-liquid state. We demonstrate that the heavy-fermion behaviour in the non-Fermi-liquid state appears to arise from the hybridized electronic states of gadolinium 5d-electrons participating in metallic Gd\u0026ndash;Gd and covalent Gd\u0026ndash;C bonds. These results accentuate unusual chemical bonds in CGd\u003csub\u003e6\u003c/sub\u003e octahedra with the dual characters of gadolinium 5d-electrons for the emergence of heavy-fermions.\u003c/p\u003e","manuscriptTitle":"Unusual d-electron heavy-fermion behaviour in f-electron ferromagnetic antiperovskite Gd3SnC","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-03-25 13:53:58","doi":"10.21203/rs.3.rs-336915/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d2790558-305f-4611-a9c7-7c1c274ede39","owner":[],"postedDate":"March 25th, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":3217288,"name":"Magnetics Materials and Devices"},{"id":3217289,"name":"Soft Condensed-matter Physics"},{"id":3217290,"name":"Hard Condensed-matter Physics"}],"tags":[],"updatedAt":"2021-04-16T13:36:40+00:00","versionOfRecord":[],"versionCreatedAt":"2021-03-25 13:53:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-336915","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-336915","identity":"rs-336915","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}