Properties of the localized-spin-fluctuating systemPtCo. I. Susceptibility and magnetization

Abstract

A Pt—0.061-at.%-Co sample has been examined as follows: (i) susceptibility measurements from 1.5 to 60 K in a field of 4.6 kOe; (ii) magnetization measurements from 1.6 to 10 K in fixed fields of 10, 25, and 59 kOe, and also at fixed temperatures of 1.6, 4.2, and 10.3 K in fields varying up to 59 kOe. The susceptibility data (which indicate an effective-moment reduction below 10 K) have been analyzed in terms of two phenomenological expressions, both of which fit the data equally well. The first $\Delta \chi \mathrm{}\left(T\right)\mathrm{}\propto \frac{{\mu }_{\mathrm{eff}}^2}{(T+\ominus )}$ yields ${\mu }_{\mathrm{eff}}=5.7\mathrm{}{\mu }_B$ and an impurity characteristic temperature of $\ominus =1.8\mathrm{}$ K. The second $\Delta \chi \mathrm{}\left(T\right)\mathrm{}\propto [\frac{n_s{\mu }_{\mathrm{eff}}^2}{T}+\frac{n_{\mathrm{us}}{\mu }_{\mathrm{eff}}^2}{(T+\ominus )}]$, where $n_s$ and $n_{\mathrm{us}}$ are the number of stable and unstable (fluctuating) impurity moments, respectively, gives $\ominus =3.4\mathrm{}$ K, ${\mu }_{\mathrm{eff}}=5.6\mathrm{}{\mu }_B$, and an interaction range—within which two interacting Co moments stabilize each other—of about 230 lattice sites. The magnetization data are complex, and have not been analyzed quantitatively. Qualitatively these data can be understood by phenomenologically introducing an effective temperature $T_{\mathrm{eff}}^2=T^2+{\left(\frac{g{\mu }_B}{k_B}\right)}^2{H}^2$, which can account for both the more rapid approach to saturation of the constant-field magnetization curves as compared with the constant-temperature curves (when plotted against $\frac{H}{T}$), and the field dependence of the saturated limit of these constant-field curves.