Induction of ferromagnetism in multiferroic LaFeO₃ by doping with Ni²⁺

In this research, LaFeO₃ doped with different concentrations of Ni²⁺ at Fe sites, ranging from 0.1 to 0.5 with a Δx of 0.1, was studied. The synthesis process involved high-energy milling followed by heat treatment at a low temperature, 1073 K, to induce ferromagnetic order (FM). Moreover, the effects of cation doping on the crystal structure and multiferroic properties were determined. X-ray diffraction analysis and Rietveld refinement confirmed that doped lanthanum ferrite with an orthorhombic structure (Pnma) was obtained for all the studied dopant levels. The magnetic hysteresis loops change from antiferromagnetic (AFM) to weakly ferromagnetic at room temperature when Ni²⁺ is introduced into the LaFeO₃ crystal structure, which is attributed to spin canting due to the difference in ionic radius between the Fe³⁺ and Ni²⁺ cations and to the frustration of the magnetic cycloid due to the existence of uncompensated ions. Regarding the dielectric properties, the doped ferrites show semiconductor behavior with high values of relative permittivity as the doping concentration increases. XPS spectra confirmed the existence of adsorbed oxygen associated with oxygen affinity as a mechanism of charge compensation due to vacancies and oxidation from Fe³⁺ to Fe⁴⁺.