Synthesis and structural, magnetic, thermal and electronic properties of Mn-doped ZnCr2Se4

Abstract Polycrystalline compounds of the Zn x Mn y Cr z Se 4 system ( x + y + z ≈ 3) crystallizing in a cubic spinel structure were successfully synthesized in the concentration range of x = 0.11÷0.46 using the ceramic method. The influence of manganese on microstructure, magnetic, thermal and electronic properties was investigated. X-ray studies confirmed that the spinel phase forms throughout the entire range ( x = 0.1÷0.5). The results of magnetic measurements showed that the studied compounds are antiferromagnets with the Neel temperature of T N = 12÷25 K and the Curie-Weiss temperature increasing from θ = 87 K for x = 0.11 to θ = 110 K for x = 0.46. Below T N , the magnetic field dependence of magnetization shows two peculiarities at critical fields H c1 (connected with metamagnetic threshold accompanied with transition from a helical to a conical phase) and H c2 (where the conical magnetic structure transforms into a ferromagnetic phase). The values of H c1 remain almost constant while the values of H c2 shift into lower magnetic fields as the Mn content increases. These effects are interpreted in terms of the superexchange integrals for the first two coordination spheres including spin defects and non-stoichiometry. The XPS study is consistent with FPLO calculation and discerned Mn 2+ charge states. The effects of different concentrations of Zn, Mn and Cr have been demonstrated by XPS experimental results. DSC/TG analysis indicates that the presence of Mn ions in the ZnCr 2 Se 4 crystal lattice affects the stability and resistance of the doped compounds in comparison with the pure ZnCr 2 Se 4 .