Thermodynamic and Transport Properties of RCuAs₂ Single Crystals (R = Y, La-Nd, Sm, Gd-Yb)

The RCuAs₂ (R = rare-earth) compounds crystallize in HfCuSi₂-type tetragonal structure and compounds with moment bearing R-ions order antiferromagnetically at low temperatures. In particular, resistivity curves on polycrystal samples for R = Sm, Gd, Tb, and Dy show an unexpected resistivity minimum above their magnetic ordering temperatures [1]. To study the origin of the minimum with negligible 4f-hybridization, single crystals of RCuAs₂ have been grown and characterized by XRD, specific heat, resistivity, and magnetization measurements. Magnetization measurements for this family clearly indicate local moment behavior with a large degree of anisotropy between H || ab and H || c due to the CEF effect. All physical property measurements clearly indicate antiferromagnetic ordering at low temperatures for R = Sm - Yb. Although the resistivity value of single crystals is significantly smaller than that for polycrystalline samples, resistivity data for R = Sm, Gd, Tb, and Dy exhibit a pronounced minimum above their magnetic ordering temperatures. In this talk we will present physical property measurements for this family and discuss the possible origin of the resistivity minimum by considering the Kondo and RKKY interactions.
[1] E. Sampathkumaran, et. al, PRL 91, 036603 (2003)