Mossbauer studies on exchange interactions in CoFe2O4

Two polycrystalline samples of CoFe2O4 were prepared by slow cooling and quenching and studied using Mossbauer spectroscopy and X-ray diffraction. The crystals were found to have a cubic spinet structure with the lattice constants of the slowly cooled sample being a(0) = 8.381 Angstrom and the quenched sample being a(0) = 8.391 Angstrom. The temperature dependence of the magnetic hyperfine field in Fe-57 nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the Neel theory of ferrimagnetism. For the slowly cooled sample, the intersublattice A-B superexchange interaction and intrasublattice A-A superexchange interaction were anti ferromagnetic with a strength of J(A-B) = -25.0 k(B) and J(A-A) = - 18.9k(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.