Evidence of reentrant behavior in nanoparticles of ferrite in ferrofluids

Ferrofluids made up of mixed ferrite particles Mn1-xZnxFe2O4 mono-dispersed in glycerol have been studied by ferromagnetic resonance (FMR) in X band a nd by magnetization measurements in the temperature range of 3.5-300 K. FMR spectra have been recorded on field-cooled samples. Some features of these spectra are typical of a transition from ferro to spin-glass state, i.e. a reentrant behavior. By taking relaxation into account in the frame of Land au Lifchitz formalism, the freezing temperature T-f,= 40K was accurately de termined, in good agreement with temperature measurements of the static mag netic susceptibility of field-cooled ferrofluid samples. (C) 1999 Published by Elsevier Science B.V. All rights reserved.