R2CoAl3(R=Y and 鑭系元素)三元稀土化合物之物性研究

Abstract

The crystal structure, electrical resistivity (ρ) and magnetic susceptibility (χdc of the R2CoAl3 (R = Y and rare earth element) compounds are investigated. Powder X-ray diffraction patterns reveal that all the samples crystallize in the cubic MgCu2 type structure except Ho and Er and lattice parameters are found to decrease monotonically from 8.1A to 7.7 A with increasing the atomic number of R. Structure transforms from cubic to hexagonal in Ho and Er sample The ρ(T) curve of La2CoAl3 drops to zero at 6 K and the diamagnetic behavior observed in χdc(T) curve confirms the presence of bulk superconductivity with Tc=6K and ΔTc=1K. Above the superconducting transition temperature the ρ(T) curve exhibit a metallic behavior. The ρ(T) curves of R2CoAl3 (R =Sm, Tb, Ho, and Er ) compounds shows the etallic behavior with local minima at low temperature. The χdc(T) vurves for all samples studied follow the Curie-Weiss behavior for T > 150 K except Sm, with the obtained value of effective moments μeff slightly larger than the moment of the corresponding R3+ ions. The occurrence of anomaly in the χdc(T) curves and a drop off in the ρ(T) curve at the corresponding temperatures indicate that antiferromagnetic transition occurs in R2CoAl3 (R = Ce, Pr and Nd) and ferromagnetic transition in Sm2CoAl3 and Tb2CoAl3 compounds.