Anisotropy of the low temperature resistivity of hexagonal single crystalline spin glass systems

Abstract

The impurity contribution to the resistivity in zero field Δρ(T) of dilute hexagonal single crystals of ZnMn, CdMn and MgMn has been studied in the mK range on samples cut parallel (‖) and perpendicular (⊥) to thec-axis, using a SQUID technique for the measurements. Typical spin glass behavior is found in Δρ_⊥(T) as well as Δρ_‖(T) for all alloys, with Kondo like logarithmic increases at higher temperatures and maxima atT _m at lower temperatures, indicating the influence of impurity interactions. The differences in the corresponding isotropic resistivity Δρ_poly(T) between the three systems can qualitatively be understood within the framework of a theoretical model by Larsen, describing Δρ(T) as a function of universal quantitiesT/T _K and Δ_RKKY/T _K , where Δ_RKKY is the RKKY-interaction strength andT _K the Kondo temperature. With respect to the two lattice directions studied, the behavior of Δρ_⊥(T and Δρ_‖(T is anisotropic in the Kondo regime as well as in the range where ordering becomes important. While the anisotropy in the Kondo slope can be understood by an anisotropic unitarity limit, the understanding of the anisotropy in region where impurity interactions are important remains problematic.