Preparation, structure and magnetic, electronic and thermal properties of Dy3+-doped ZnCr2Se4 with unique geometric type spin-glass

Physico-chemical studies of (Zn1-xDyx)Cr2Se4 and Zn[Cr2-xDyx]Se-4 spinel systems (x = 0.05, 0.10) containing dysprosium ions in both tetra- and octahedral positions have shown an enhancement of long-range antiferromagnetic interactions and a weakening of short-range ferromagnetic ones. This resulted in the appearance of geometric type spin-glass in connection with the increase in the length of chemical bonds between chromium ions. This state of spin-glass is also due to the large difference in the absolute values of the superexchange integrals and the small magnetic contribution to the specific heat below the freezing point. Studies of XPS and X-ray absorption near edge structure (XANES) showed that no main edge shift was observed between the tetra- and octahedral positions of dysprosium ions, which indicates that they remain in the +III oxidation state. Thus, significant differences between the effective magnetic moment and the effective number of Bohr magnetons, as well as much higher saturation magnetization values above 6 mu(B) , suggest that chromium ions may have a different oxidation state. These effects may be also generated by spin defects.