Anisotropy induced by nonmagnetic impurities inCuMn spin-glass alloys

Recent measurements on $\mathrm{Cu}$ Mn spin-glass alloys have revealed that the anisotropy field maintaining the remanent magnetization in the direction of the initial applied field is strongly enhanced by the addition of nonmagnetic Au or Pt impurities. A similar enhancement of the anisotropy field of $\mathrm{Cu}$ Mn spin-glass alloys by nonmagnetic impurities is also indicated by ESR measurements. We show that these results can be accounted for by the existence of Dzyaloshinsky-Moriya-type interactions between the Mn spins arising from spin-orbit scattering of the conduction electrons by nonmagnetic impurities. We derive this interaction by using third-order perturbation theory on the conduction electrons and by retaining only the terms in the energy which are first order in the spin-orbit coupling of the nonmagnetic impurity. To calculate the macroscopic anisotropy energy from the anisotropic pair interaction, it is necessary to make some assumptions because of our incomplete knowledge of the spin-glass state. We are able to justify our assumptions a posteriori by comparing our predictions to the experimental results. In particular, we are able to explain the variation over two decades of the anisotropy energy with the type of nonmagnetic transition-metal impurity.