Magnetization of a dilute magnetic alloy with magnetic interactions: ZnMn

We have measured the magnetization M up to 50 kG at low temperatures (1.2-4.2 K) of a series of ZnMn alloys (n=60-2500 ppm Mn). For the alloys studied, the measured magnetization is dominated by impurity-impurity interactions via the indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) potential V(r)=(V₀cos2kFr)r³. These interactions reduce M below the Brillouin function BS(H/T) appropriate for free spins, and also inhibit the approach to saturation of M. In the limit n→0, the measured M remains below the free-spin Brillouin function. For the n=60, 112, and 213 ppm Mn alloys and for gμBHkBT, we find M=gμBSn[1-H₀(n,T)H], where S is the spin of the Mn impurity and H₀(n,T)=AkBT+BnV₀. For these alloys we find A/B=0.16±0.03 and V₀=(1.7±0.4)×10^-36 erg cm³. The term AkBT in H₀(n,T) may represent a single-impurity (Kondo) effect, while the term BnV₀ clearly represents the effects of the RKKY potential. Scaling behavior is observed for the magnetization once the concentration dependence of the impurity spin S is accounted for the in the following way: M/nS(n)=F₁(T/n,H/n). However, deviations from scaling of M are observed for the 2500-ppm Mn alloy where evidence has been found for additional interactions not of the RKKY type. The scaling behavior of the zero-field magnetic susceptibility is also presented.