Effect of Ho³⁺ Substitution on Magnetic Properties of ZnCr₂Se₄

A series of ZnCr_2-HoSe₄ microcrystalline spinels (where x = 0.05, 0.075, and 0.10) containing holmium ions in octahedral coordination were obtained by sintering of adequate reactants at high temperatures. The obtained doped materials were characterized by X-ray diffraction, Scanning Electron Microscopy, UV-Vis-NIR, molecular field approximation, and XPS spectroscopies. Their thermal properties were also investigated. The doping of the ZnCr₂S₄ matrix with paramagnetic Ho³⁺ ions with a content of not more than 0.1 and a screened 4f shell revealed a significant effect of orbital and Landau diamagnetism, a strong reduction in short-range ferromagnetic interactions, and a broadening and shift of the peak of the first critical field by simultaneous stabilization of the sharp peak in the second critical field. These results correlate well with FPLO calculations, which show that Cr sites have magnetic moments of 3.19 µ_B and Ho sites have significantly larger ones with a value of 3.95 µ_B. Zn has a negligible magnetic polarization of 0.02 µ_B, and Se induces a polarization of approximately -0.12 µ_B.