Mössbauer Studies on Exchange Interactions in CoFe2O4

Abstract

Two polycrystalline samples of CoFe2O4 were prepared by slow cooling and quenching and studied using Mössbauer spectroscopy and X-ray diffraction. The crystals were found to have a cubic spinel structure with the lattice constants of the slowly cooled sample being a0=8.381 Å and the quenched sample being a0=8.391 Å. The temperature dependence of the magnetic hyperfine field in 57Fe nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the Néel theory of ferrimagnetism. For the slowly cooled sample, the intersublattice A–B superexchange interaction and intrasublattice A–A superexchange interaction were antiferromagnetic with a strength of JA–B=-25.0kB and JA–A=-18.9kB, respectively, while the intrasublattice B–B superexchange interaction was ferromagnetic with a strength of JB–B=3.9kB. In the quenched sample, however, their strengths were JA–B=-22.6kB, JA–A=-17.6kB, and JB–B=3.9kB, respectively.