Effect of crystal field on the magnetization of dilute hcp alloys

Magnetization measurements on very dilute single-crystal alloys of Mg-Mn, Zn-Mn, and Zn-Cr in the temperature range of 2-0.008 K show that the ground state of these systems is determined by fine-structure splitting. For Mg-Mn the fine-structure constant $D$ is +0.006 K with an effective spin of $\frac{5}{2}$ while for Zn-Mn $D$ is -0.07 K and for Zn-Cr it is +0.08 K for an effective spin of 1 in both cases. Over our temperature range there is no evidence for a Kondo spin-compensated state. For all impurity concentrations, even the 1 ppm level, Ruderman-Kittel-Kasuya-Yosida interactions play an important role as determined from magnetization measurements of polycrystalline Zn-Mn alloys.