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

Synopsis

The compounds of form RCuAs2 (R = rare-earth) exhibit a variety of unusual behaviours in their physical properties. In particular, resistivity curves on polycrystalline samples for R = Sm, Gd, Tb, and Dy show an unexpected resistivity minimum above their magnetic ordering temperatures. To study the origin of the minima in these compounds, single crystals of RCuAs2 have been grown and characterized by XRD, specific heat, resistivity, and magnetization measurements. These compounds, with the exception of R = La, crystallize in the HfCuSi2-type tetragonal structure and compounds with magnetic moment bearing R-ions order antiferromagnetically at low temperatures.  Magnetization measurements for this family clearly indicate local magnetic moment behavior with a large degree of anisotropy between fields applied to the H || ab and H || c lattice directions 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 I will present physical property measurements for this family and discuss the possible origins of the unusual observed behaviour by considering the Kondo and RKKY interactions.