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 magnetic properties of mechano synthesized LaFeO₃ nanoparticles (30–40 nm), their Eu³⁺-doped (La_0.70Eu_0.30FeO₃), and Eu³⁺/Cr³⁺ co-doped (La_0.70Eu_0.30Fe_0.95Cr_0.05O₃) variants 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 Eu²⁺ ions were detected on the surfaces of the nanoparticles. The nanoparticles consist of antiferromagnetic cores flanked by ferromagnetic shells. The Eu³⁺ dopant ions enhance the magnetization values relative to those of the pristine nanoparticles and result in magnetic susceptibilities compatible with the presence of Eu³⁺ van Vleck paramagnetism of spin–orbit coupling constant (λ = 363 cm⁻¹) and a low temperature Curie–Weiss like behavior associated with the minority Eu²⁺ 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.