Strain induced magnetism and superexchange interaction in Cr substituted nanocrystalline cobalt ferrite

Abstract

Distribution of magnetic relaxation time using Mössbauer spectroscopy has been observed for CoFe2-xCrxO4 (0.1 ≤ x ≤ 0.4) annealed at lower temperature (≤400 °C). The estimated cation distribution over A and B sites observed by Mössbauer spectroscopy is consistent with that obtained by the Rietveld analysis of the X-ray diffraction patterns. Saturation magnetization and magnetocrystalline anisotropy constant increase up to 20% of Cr (x = 0.2) substitution and, decrease with further increase of x. However, the coercive field as well as the Néel temperature decreases with increase in Cr3+ concentration, i.e., a crossover from the hard magnetic to soft magnetic nature by Cr substitution at the Fe site of CoFe2O4 has been observed. This behavior is attributed to the competition between strain induced magnetism and superexchange interaction between cations.