Superexchange interactions of In3+ substituted CoFe2O4

Polycrystalline samples of CoFe2-xInxO4 (0 <= x <= 0.5) ferrite were prepared by slow cooling and studied using Mossbauer spectroscopy, X-ray diffraction and vibrating sample magnetometry(VSM). The crystals were found to have a cubic spinel structure. The lattice parameter (a(0)) increased linearly with increasing In concentration x. The Mossbauer spectra of CoFe2-xInxO4 were measured at various temperatures from 17 to 825 K. The isomer shifts indicated that the valence states of the irons at both tetrahedral (A) and octahedral (B) sites were in ferric high-spin states. The Neel temperature of CoFe1.9In0.1O4 was T-N = 765 +/- 3 K. The Debye temperatures for the A and the B sites of CoFe1.9In0.1O4 were found to be Theta(A) = 664 +/- 5 K and Theta(B) = 207 +/- 5 K, respectively. The temperature dependences of the magnetic hyperfine fields at Fe-57 nuclei at the tetrahedral (A) and the octahedral (B) sites were analyzed by using the Neel theory of ferrimagnetism. The intrasublattice A-O-B and the intersublattice A-O-A superexchange interactions of CoFe1.9In0.1O4 were found to be antiferromagnetic with strengths of J(A-B) = -14.7 k(B) and J(A-A) = -3.6 k(B), respectively, while intrasublattice B-O-B superexchange interaction was ferromagnetic with a strength of J(B-B) = 7.4 kB. The VSM data showed that the saturation magnetization decreased with increasing x from about 83.7 emu/g for x = 0.1 to 63.6 emu/g for x = 0.5.