Conduction-electron—local-moment exchange coupling in diluteCu MnandAg Mn

Abstract

The theory of spin-density oscillations (SDO) caused by local-moment—conduction-electron ($s-d$) exchange in simple metals is reviewed and restated in terms of spherical components of the exchange interaction on the Fermi surface. Both direct and $s-d$ mixing exchange sources are included, and calculations are presented to account for the effects of potential scattering, in terms of phase shifts, and conduction-band exchange enhancement of the SDO. The SDO amplitude is related to inhomogeneous broadening of host nuclear-magnetic-resonance lines using the theory of such broadening given recently by the authors. The measurements of $s-d$ exchange parameters by impurity-state susceptibility and EPR linewidth are also discussed, with particular emphasis on the effect of conduction-band exchange on these phenomena. We apply the above considerations to the alloy systems $\mathrm{Cu} \mathrm{Mn}$ and $\mathrm{Ag} \mathrm{Mn}$. For $\mathrm{Cu} \mathrm{Mn}$, estimates of the predominant $s-d$ mixing exchange from (i) ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ NMR linewidths, (ii) Mn impurity-state susceptibility, and (iii) indirect high-temperature measurement of the single-impurity EPR linewidth are compared. Values so obtained range over a factor of ∼ 1.5 with the SDO values smallest and the susceptibility values largest. This variation is in apparent conflict with the Hartree-Fock solution of the Anderson model. The exchange values found may also be combined with the Anderson-model theory to establish an upper limit of ∼ 5.5 $d$ electrons on the Mn site. For $\mathrm{Ag} \mathrm{Mn}$ the impurity susceptibility corresponds to a rather smaller mixing exchange coupling in agreement with recent EPR work by Davidov et al. The ${}_{}{}^{109}{}_{}{}^{}\mathrm{Ag}$ NMR linewidth results of Mizuno are shown to be caused by more than one species of broadening agent, preventing a firm conclusion on the SDO measurement of exchange from being drawn.