Abstract
Polycrystalline samples of CoFe2.xInxO4 (0 x 0.5) ferrite were prepared by slow cooling and studied using M¨ossbauer spectroscopy, X-ray diffraction and vibrating sample magnetometry( VSM). The crystals were found to have a cubic spinel structure. The lattice parameter (a0) increased linearly with increasing In concentration x. The M¨ossbauer 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 N´eel temperature of CoFe1.9In0.1O4 was TN = 765 ± 3 K. The Debye temperatures for the A and the B sites of CoFe1.9In0.1O4 were found to be A = 664 ± 5 K and B = 207 ± 5 K, respectively. The temperature dependences of the magnetic hyperfine fields at 57Fe nuclei at the tetrahedral (A) and the octahedral (B) sites were analyzed by using the N´eel 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 JA.B = .14.7 kB and JA.A = .3.6 kB, respectively, while intrasublattice B-O-B superexchange interaction was ferromagnetic with a strength of JB.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.