Influence of Ti substitution on the critical properties of Cu_xCr_yTi_zSe_4 (z = 0.24 and 0.35)

摘要

Magnetization, M, and susceptibility, X, measurements of Cu_xCr_yTi_zSe_4 (z = 0.24 and 0.35) showed both strong lowering of magnetic moment in comparison with CuCr_2Se_4 matrix and zero-field-cooling (ZFC) - field-cooling (FC) susceptibility splitting characteristic for the spin-glass (SG) behaviour. Isothermal magnetization curves, M(H), easy saturate and large values both of the Curie (T_C ～ 250 K) and Curie-Weiss (θ ～ 280 K) temperatures indicate the ferromagnetic order which coexists with the SG state. The critical behaviour of polycrystalline Cu_xCr_yTi_zSe_4 spinels investigated around the paramagnetic-ferromagnetic (PM-FM) phase transition revealed that the values of critical exponents are close to those predicted by the mean field model for long-range interactions. It means that the Ti-substitution changes the ferromagnetic critical properties described by the Heisenberg model for the matrix CuCr_2Se_4 to the mean-field estimates for Cu_xCr_yTi_zSe_4.