Structural and magnetic properties of zinc ferrite aluminates

Abstract

Zinc ferrite aluminates ZnAlxFe₂₋xO₄ with composition (0≤ x ≤1) were synthesized at 1150C using the usual ceramic method and studied by X-ray diffraction, magnetization and Mössbauer measurements. It is observed that lattice parameter decreases, with increasing Al concentration (x). Mössbauer absorption spectra of all the samples recorded at room temperature showed three hyperfine magnetic sextets and a single quadrupole doublet. The outer sextet is assigned to ⍺- Fe₂O₃ crystalline phase, whereas inner two sextets refer to Fe³⁺ ions at octahedral (B) site and tetrahedral (A) site showing the formation of zinc ferrite aluminates phase. The hyperfine magnetic field was found to decrease with increasing Al concentration and has been explained on the basis of super transferred hyperfine field. The central doublet is partially dissociated forming ZnFeO₂ (delafossite) phase overlapping the main Mössbauer spectra measured at room temperature. The observed variations in saturation magnetization in all the samples have been explained on the basis of site distribution and the strength of the exchange interactions between the magnetic ions. On the basis of these observations, it is concluded that the present ferrite system exhibits a non-collinear magnetic structure with a very weak ferromagnetic character, which starts dominating further when zinc ferrite is diluted with non-magnetic Al³⁺ ions.