Characteristic temperatures in the spin-glassAuFe

Abstract

The binary-alloy system $\mathrm{Au}\mathrm{Fe}$ with varying concentration, $c$, of Fe is shown to have three distinct regimes with quite different physical properties. These are the Kondo regime at low con\ifmmode \acute{c}\else \'{c}\fi{}entrations, the spin-glass regime at intermediate concentrations, and the dilute-ferromagnet regime at high concentrations. This paper contains a comprehensive compilation of experimental data expressed in terms of characteristic temperatures, like, for example, the spin-glass freezing temperature and the temperature of the resistance maximum. A coincidence of the characteristic temperatures is evident in the spin-glass regime $0.05%\ensuremath{\lesssim}c\ensuremath{\lesssim}15%$. Here a recent theoretical calculation based on the Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect-exchange interaction between the Fe spins accounts quantitatively for the observed dependence on concentration and electronic mean free path in a variety of different experiments. This includes, for example, recent experiments in quench-condensed films showing a large mean-free-path effect on the resistance maximum. The agreement extends to remarkably high concentrations and demonstrates substantial self-damping of the RKKY interaction. At the transition into the dilute ferromagnet regime $c\ensuremath{\gtrsim}15%$, near the threshold for nearest-neighbor percolation, there is a sharp departure of the observed freezing temperatures away from the predicted concentration dependence. This indicates a change-over between the spin-glass state dominated by the RKKY interactions and the dilute ferromagnet state dominated by nearest-neighbor direct-exchange interactions and is interpreted qualitatively in terms of recent percolation theories. Entering the Kondo regime $c\ensuremath{\lesssim}0.05%$ leads to a dispersion of the characteristic temperatures, whereby the complete agreement with the theoretical calculation is lost. Only one of the characteristic temperatures, the noise temperature derived from the resistance maximum by a method which incorporates the Kondo effect, remains in agreement with the RKKY calculation.