Study of Cation Distribution in La3+ and Eu3+ Substituted Cobalt Ferrite and Its Effect on Magnetic Properties

The rare-earth metal ion substitution in the spinel ferrites significantly alters its cation distribution, leading to changes in their structural and magnetic properties. Herein, we have studied the structural and magnetic behaviour of rare-earth (RE = La3+ and Eu3+) substituted cobalt ferrites (CoFe2-xRExO4; x = 0.03 per f. u.) synthesized using the conventional solid-state route. Both the samples possess a cubic structure with Fd (3) over barm space group. Substituting La3+ and Eu3+ creates a structural distortion and compresses the lattice parameter and unit cell volume of CoFe2O4 due to their large ionic radii compared to Fe3+. Raman spectroscopy pattern confirms the cubic structure of the samples; however, the variation in the intensity of A(1g) modes suggests the occurrence of cation redistributions. The inversion parameter (i) value calculated using the MOssbauer spectroscopy is 0.78, suggesting that pristine CoFe2O4 has a mixed spinel state. Furthermore, the 'i' value decreased to 0.69 and 0.66, respectively, upon incorporating La3+ and Eu3+ cations, confirming the occurrence of cation redistributions in the samples. Besides, the decreased probability of super-exchange interaction and reduction in the magnetic behaviour are caused by the migration of Co2+ cation from the octahedral-[B] site to the tetrahedral-(A) site and partial replacement of Fe3+ ion by RE3+ elements.