The spin glass behaviour of disordered spinel ferrite Co₂TiO₄

Abstract

AC susceptibility ( chi ) measurements have been carried out in disordered spinel ferrites Co₂TiO₄, Co₂SnO₄ and Co_1.2Zn_0.8TiO₄ between 1.7 and 100 K. The last two systems are studied in order to understand the puzzling result for Co₂TiO₄. The measurements show as many as five peaks in the chi against T curve of this system. In Co₂SnO₄ only three chi peaks, and in Co_1.2Zn_0.8TiO₄ only one chi peak, are seen. DC magnetisation and neutron diffraction studies by earlier workers have shown Co₂TiO₄ and Co₂SnO₄ to be re-entrant systems and Co_1.2Zn_0.8TiO₄ to be a spin glass below about 16.5 K. Furthermore, whereas A site canting is present in Co₂TiO₄, Co₂SnO₄ has collinear magnetic structure indicating strong A-B coupling. On the basis of all these results it is concluded that the A and B site spins in Co₂TiO₄ freeze separately, which is a consequence of the weak A-B coupling in this system. The nature of the variation in the position of the chi peaks with the applied DC field, H, supports this pictures. H is applied collinearly to the AC field.