Mössbauer characterisations and magnetic properties of iron cobaltites CoxFe3ÿxO4 (1rxr2.46) before and after spinodal decomposition

Iron cobaltite powders CoxFe3ÿxO4 (1rxr2.46) were synthesized with compositions in between the cobalt ferrite CoFe2O4 and Co2.46Fe0.54O4. The cationic distribution of pure spinel phases was determined by Mössbauer spectroscopy: as Co content increases in the spinel oxide, Co cations replace Fe cations in the octahedral sites and Co cations migrate from octahedral to tetrahedral sites. Saturation magnetizations MS measured at 5 K by a SQUID magnetometer were consistent with the values calculated from the cationic distribution. MS decreases as diamagnetic Co 3þ cations replace strongly magnetic Fe cations. Two spinel phases were formed by spinodal decomposition of Co1.73Fe1.27O4 phase submitted to a subsequent thermal treatment, one with a high amount of iron Co1.16Fe1.84O4 and one other containing mostly cobalt Co2.69Fe0.31O4. Increase of the experimental MS value obtained after the spinodal decomposition is in accordance with the calculated value deduced from the cationic distribution of the two phases.