Magnetic properties of Cu1-xMxFe2-2xO4 mixed ferrites (M = Ge,Ti, 0 <= x <= 0.4)

Spinnel copper ferrites Cu1+xMxFe2-2x,O-4 (M-Ge, Ti) with 0 less than or equal to x less than or equal to 0.4 have been investigated using Mbssbauer spectroscopy and magnetic measurements. Mossbauer measurements performed at 77 and 300K 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 (M-S) measurements were performed using a vibrating sample magnetometer in the temperature range of 77-750 K, while magnetic susceptibility (chi(m)) measurements were performed using a Faraday microbalance susceptometer in the range of 500-1000 K. Both M-S and chi(m) variations with temperature indicate that the Curie temperature T-C decreases almost linearly with increasing Ti and Ge concentrations. The magnetic moments calculated from the M-S data and the effective paramagnetic moments calculated from chi(m) data are discussed on the basis of Neel's two sublattice molecular field model and the cations distribution obtained from the Mbssbauer analysis. (C) 2003 Elsevier B.V. All rights reserved.