Moessbauer study of the re-entrant spin-glass behaviour in the mixed spinel ferrites Mg(0.9+x)Fe2(1-x)Ni0.1TixO4 (x=0.5 and 0.6)

Samples of the mixed spinel ferrite series Mg(0.9+x)Fe2(1-x)Ni0.1TixO4 with x=0.5 and 0.6, prepared by solid state reaction of the appropriate oxides, have been investigated with 57Fe Moessbauer spectroscopy. The as-prepared samples are found to be mainly superparamagnetic due to magnetic cluster formation. Samples after at least three times reheated exhibit spectra, which can be rather interpreted by a transversal relaxation of the spin above and spin-glass behaviour below the respective freezing temperatures Tf. External-field spectra reveal the canting to occur only on the octahedral sites. From the derived transition temperatures and thresholds together with data from earlier investigated sample with x=0.7 a compositional magnetic phase diagram for this spinel series is obtained.