Mössbauer Studies of Cation Distribution in Zn $_{{\rm x}}$ Co $_{0.5 mathchar$

The crystal structure of Zn_xCo_0.5-xFe_2.5O₄, prepared by a solvothermal reaction method, showed cubic spinel structure with space group Fd-3 m based on Rietveld refinement. The lattice constant a₀ increased linearly with the Zn concentration from to 0.5. Field emission scanning electron microscope (FE-SEM) measurements showed that the size of the monodispersed particles was around 300-400 nm. With increasing Zn concentration, the saturation magnetization increased from 80.3 to 109.7 emu/g, while the coercivity at 293 K decreased from 893 to 46 Oe, respectively. The magnetocrystalline anisotropy constants (K₁) were determined as 1.62, 1.32, and 1.16×10⁶ erg/cm³ for x= 0.25, and 0.5, respectively, based on the law of approach to saturations (LAS) method. We have investigated the cation distribution by Mössbauer spectroscopy, closely related to K₁. We have analyzed the recorded Mössbauer spectra as 3 sets with six-lines of tetrahedral site, and octahedral B₁ and B₂ sites both at 4.2 and 293 K. From the isomer shift values, the valence states of A and B₁ site were determined to be ferric (Fe³⁺), while that at B₂ site to be ferrous (Fe²⁺). The corresponding area ratio of A site decreased from 40 to 30 % while that of B site increased from 60 to 70% as the Zn concentration changed from x = 0 to 0.5 both at 4.2 and 293 K. Here, the changes in the area ratios of A and B sites are due to the changes in the cation distributions at the A and B sites, being originating from the randomly substituted Zn ions in Zn_xCo_0.5-xFe_2.5O₄ microspheres.