Magnetic properties of Cu1+xMxFe2−2xO4 mixed ferrites (M=Ge,Ti, 0⩽x⩽0.4)

Abstract Spinnel copper ferrites Cu1+xMxFe2−2xO4 (M=Ge, Ti) with 0⩽x⩽0.4 have been investigated using Mossbauer spectroscopy and magnetic measurements. Mossbauer measurements performed at 77 and 300 K show broadened magnetic sextets superimposed on a paramagnetic doublet. The magnetic components have been assigned to Fe3+ in two non-equivalent crystallographic tetrahedral and octahedral sites. The Mossbauer data show that Ge4+ has strong preference to occupy the tetrahedral site in contrast to Ti4+ which occupy the octahedral site. Saturation magnetization (MS) measurements were performed using a vibrating sample magnetometer in the temperature range of 77–750 K, while magnetic susceptibility (χm) measurements were performed using a Faraday microbalance susceptometer in the range of 500–1000 K. Both MS and χm variations with temperature indicate that the Curie temperature TC decreases almost linearly with increasing Ti and Ge concentrations. The magnetic moments calculated from the MS data and the effective paramagnetic moments calculated from χm data are discussed on the basis of Neel's two sublattice molecular field model and the cations distribution obtained from the Mossbauer analysis.