R2CuX3 (R = 鑭系元素; X = 典型元素) 三元稀土化合物之物性研究

Abstract

Ternary R2CuX3 (R = La, Ce and Pr; X = Al, In, Si and Ge) compounds have been prepared by arc-melting method. X-ray analysis reveals all the samples are single phases. The AC electrical resistivity (ρ), magnetic susceptibility (χdc and χac) and heat capacity (C) of these compounds were measured. The DC and AC susceptibility curves reveal spin-glass behavior for all R2CuX3 samples (except R = La, and Ce2CuAl3). Interestingly, the susceptibility measurement shows that Pr2CuGe3 may have two ferromagnetic to spin-glass transitions. The nonmagnetic atom-disorder in crystal structure might be necessary to be responsible for the spin-glass behavior. The effective magnetic moments of the rare earth ions were calculated by using Curie-Weiss law from DC susceptibility data. The heat capacity data are obtained for Ce2CuAl3, Pr2CuAl3, Ce2CuSi3 and Pr2CuSi3. The effective mass of electron of these compounds was calculated. The γvalues of Ce2CuAl3, Pr2CuAl3 and Pr2CuSi3 are enhanced ten to hundredfold comparing to those of the normal metals. The C(T) curve of Pr2CuAl3 shows a broad maximum around Tf. The C/T versus T2 curve of Ce2CuAl3 and Ce2CuSi3 diverges as temperature decreasing to around 2 K. The ρ(T) exhibits metallic behavior in all the samples at high temperature range. The ρ(T) curve of La2CuAl3 shows the superconducting phase transition at 4.4 K. In the Ce2CuX3 compounds, the ρ(T) curves show the local minimum at low temperatures, which are the typical behavior of Kondo compounds. Neither the singularity nor rapidly change of ρ(T) are found around Tf in spin-glass compounds. Interestingly, the ρ(T) curve of Pr2CuGe3 exhibits two sharp local minimum around 14 K and 6 K, supporting two ferromagnetic transitions of Pr2CuGe3.