Core and surface structure and magnetic properties of mechano- synthesized LaFeO3 nanoparticles and their Eu3+ -doped and Eu3+ /Cr3+-co-doped variants

The core and surface structure, and magnetism of mechano-synthesized LaFeO 3 nanoparticles (30-40 nm), Eu 3+ -doped (La 0.70 Eu 0.30 FeO 3 ), and Eu 3+ /Cr 3+ co-doped (La 0.70 Eu 0.30 Fe 0.95 Cr 0.05 O 3 ) are reported. Doping results in a transition from the O՝-type to the O-type distorted structure. Traces of reactants, intermediate phases, and a small amount of Eu 2+ ions were detected on the surfaces of the nanoparticles. The nanoparticles consist of antiferromagnetic cores flanked by ferromagnetic shells. The Eu 3+ dopant ions enhance the magnetization values relative to those of the pristine nanoparticles and result in magnetic susceptibilities compatible with the presence of Eu 3+ van Vleck paramagnetism of spin–orbit coupling constant (l = 363 cm -1 ) and a low temperature Curie-Weiss like behavior associated with the minority Eu 2+ ions. Anomalous temperature-dependent magnetic hardening due to competing magnetic anisotropy and magnetoelectric coupling effects together with a temperature-dependent dopant-sensitive exchange bias, caused by thermally activated spin reversals at the core of the nanoparticles, were observed.