Correlation between lattice strain and magnetic behavior in non-magnetic Ca substituted nano-crystalline cobalt ferrite

Magnetic nanoparticles of calcium (Ca)-substituted cobalt ferrite i.e. Co1−xCaxFe2O4 (x=0.00, 0.01, 0.015, 0.02, 0.05, 0.1, and 0.15) have been synthesized by the citric acid modified sol-gel method. X-ray powder diffraction (XRD)patterns confirm the formation of spinel phase. The particle size decreases with the Ca concentration. The Rietveld refinement of XRD patterns using the space group - Fd3̅m shows monotonically increasing of lattice parameter with the increasing concentration of Ca. The FT-IR spectrum recorded in the range of 325-1000 cm−1 and Raman spectrum obtained in the range of 88-800 cm−1 shows the formation of spinel phase belonging to Fd3̅m space group supporting structural analysis from XRD patterns. Magnetocrystalline anisotropy has been obtained using “Law of Approach (LA) to Saturation magnetization”. Saturation magnetization and remnant magnetization is maximum for 1% Ca substitution which could be due to strain mediated magnetism. However these magnetic properties decrease with the Ca substitution for the percentage above 1%. It could be due to decrease of magnetic exchange interaction in the sample. A correlation between magnetic behavior and lattice strain has been established in non-magnetic Ca substituted nano-crystalline cobalt ferrite. In order to investigate the ferromagnetic nature of the sample, Arrott plot analysis has been carried out. Difference in saturation magnetization obtained from LA to saturation and Arrott plot analysis gives the qualitative information about the influence of lattice strain on saturation magnetization.