Growth, structure and physico-chemical properties of monocrystalline ZnCr2Se4:Ho prepared by chemical vapour transport

Abstract ZnCr2Se4 single crystals doped with holmium ions having concentrations of 0.032, 0.055 and 0.084 (occupying octahedral positions) were successfully synthesised using chemical vapour transport. The crystals were characterised using various method: scanning electron microscopy (SEM), X-ray diffraction (XRD), SQUID and QD-PPMS measurements, and thermal analysis (DSC/TG). The ac and dc magnetic measurements as well as the specific heat studies with an increasing holmium content showed: 1) antiferromagnetic order with the Neel temperature of TN = 22 K, 2) positive value of the paramagnetic Curie-Weiss temperature increasing from θ = 53 to θ = 100 K, 3) a slight decrease in both the critical field Hc1 characteristic for a metamagnetic transition and the critical field Hc2 corresponding to the breakdown of the helical spin arrangement, 4) the magnetic contribution to the specific heat visible on the sharp peak at TN, which is strongly shifted to much lower temperatures as the magnetic field increases, and 5) the quite significant Sommerfeld gamma coefficient suggesting the properties of the heavy fermion of the single crystal under study. These effects are interpreted in terms of the exchange integrals including non-stoichiometry, spin and structural defects. The DSC/TG analysis confirmed thermal stability of obtained single crystals.