Mössbauer Studies on Exchange Interactions in CoFe₂O₄

Abstract

Two polycrystalline samples of CoFe 2 O 4 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 a 0 =8.381 Å and the quenched sample being a 0 =8.391 Å. The temperature dependence of the magnetic hyperfine field in 57 Fe 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 J A – B =-25.0 k B and J A – A =-18.9 k B , respectively, while the intrasublattice B – B superexchange interaction was ferromagnetic with a strength of J B – B =3.9 k B . In the quenched sample, however, their strengths were J A – B =-22.6 k B , J A – A =-17.6 k B , and J B – B =3.9 k B , respectively.