Static and dynamic properties of localized Mn moments in liquid bismuth

Abstract

We present measurements of static susceptibility and of $^{55}\mathrm{Mn}$ and $^{209}\mathrm{Bi}$ NMR shifts and relaxation times over temperatures ranging from 700 - 1400 K for a series of dilute alloys of Mn in liquid Bi. The Mn impurities, which possess a local moment similar to that of $\mathrm{Cu}\mathrm{Mn}$, are found to exhibit a Kondo temperature ${T}_{K}\ensuremath{\sim}50$ K. A plot of $^{55}\mathrm{Mn}$ shift versus measured impurity susceptibility reveals a small temperature-independent susceptibility term in addition to the Curie-Weiss term. The fluctuation rate of the Mn moment is deduced from relaxation measurements of the $^{55}\mathrm{Mn}$ nuclei, yielding a single-ion term in good agreement with the dynamic susceptibility model for Kondo systems given by G\"otze and Schlottmann, and a spin-spin Ruderman-Kittel-Kasuya-Yosida (RKKY) term in reasonable accord with realistic model calculations for nearfield RKKY exchange. Failure of the $^{209}\mathrm{Bi}$ shift to follow the Mn susceptibility is attributed to temperature-dependent transferred hyperfine coupling; a successful interpretation of this effect is made using x-ray and neutron-diffraction results to determine the temperature-dependent radial distribution function and employing a simple asymptotic model of the RKKY spin-density oscillations. The RKKY amplitude so determined is found to be anomalously large, while the phase (at near-neighbor distances) is in agreement with a recent model calculation for $\mathrm{Cu}\mathrm{Mn}$. By applying a small correction to the moment fluctuation times from liquid motion, we are also able to obtain a quantitative interpretation of the $^{209}\mathrm{Bi}$ relaxation times.