Magnetic properties of TM–Co–Fe–Ti spinel oxides (abstract)

Abstract

Spin glass-like behavior has been recently observed in a ceramic Zn0.5Co0.9Fe1.2Ti0.4O4 spinel oxide.1 This motivated our interest to study how the spin glass-like behavior of magnetic clusters in a diamagnetic matrix correlates to that of nonmagnetic or weakly magnetic clusters in a ferromagnetic matrix, Mössbauer effect, ac susceptibility, field cooled and zero field cooled magnetization, hysteresis loops, and γ–γ perturbed angular correlation (PAC) have been measured for TM0.5−xCo0.9Fe1.2+xTi0.4O4 (x=0.0 and 0.2) spinel oxide with TM=Zn and Cu. The variation of coercive field with temperature has been found to fit a double exponential function form Hc(T)=H1e−β1T+H2e−β2T where Hi and βi are constants for the sample with x=0.0 and TM=Zn. The exponential increase in coercive field can be linked to increased effective clusters arising from ions occupying A and B sites with Fe on both sites. This is in agreement with the Mössbauer measurements which show superparamagnetic fluctuations. The ac susceptibility and Mössbauer spectra for Zn0.5Co0.9Fe1.2Ti0.4O4 show a glass transition temperature (about 320 K). Room temperature PAC measurements on Hf doped samples with TM=Zn showed different interaction frequencies, consistent with magnetic order in the Fe enriched case. Different behavior is observed in the sample with Cu for which the ordering temperature is about 480 K.