The structural and magnetic behaviour of the MgFe _2-xCr _xO ₄ spinel ferrite

The crystal structure and magnetic properties of the spinel system MgFe _2-xCr _xO ₄ (with x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) have been investigated by means of X-ray diffraction (XRD), and Mössbauer spectroscopy. The XRD patterns showed the samples were single-phase cubic spinels. The 295 K Mössbauer spectra of the studied samples showed a continuous collapse of the internal magnetic field for both tetrahedral (A) and octahedral [B] sites with increasing Cr contents. Their 78 K Mössbauer spectra showed an ordered magnetic structure for both sites with the internal magnetic fields decreasing with increasing Cr contents. The continuous decrease in the internal magnetic field is interpreted in terms of the weakening of A-B exchange interaction. The cation distribution at tetrahedral (A) and octahedral [B] sites and its effect on Mössbauer parameters is studied. Mg ²⁺ ions are found to occupy both sites A and B, while Cr ³⁺ ions occupy site B only.