PdV: A System with a High Spin-Fluctuation or Kondo Temperature?

The temperature dependence of the incremental resistivity $\Delta \rho \mathrm{}\left(T\right)\mathrm{}$ of five dilute $\mathrm{Pd}\mathrm{V}$ alloys, ranging in concentration from 0.15- to 1.0-at.% V, has been measured from 1.4 to 300 K. $\Delta \rho \mathrm{}(T=0\mathrm{})\mathrm{}$ increases linearly with V content at a rate of 3.26±0.13 μΩ cm/at.% V. Between 10 and 80 K, $\Delta \rho \mathrm{}\left(T\right)\mathrm{}$ increases rapidly with increasing temperature, in a manner characteristic of Matthiessen's-rule breakdown resulting from phonon and impurity scattering with differing anisotropies. Above 80 K, however, $\Delta \rho \mathrm{}\left(T\right)\mathrm{}$ decreases smoothly with increasing temperature; various attempts have been made to fit this high-temperature variation: (i) In terms of a localized-spin-fluctuation (lsf) model, these data are well fitted by $\Delta \rho \mathrm{}\left(T\right)=C+D \ln \left[{(T^2+{\theta }^2)}^{\frac{1}{2}}\right]$, with lsf temperature $\theta$ estimated at about 160 K for isolated impurities. $D$, however, does not scale linearly with the V concentration $c$, and it is necessary to postulate that interimpurity interactions significantly raise $\theta$ for the interaction pair, then $D\propto c{\mathrm{}(1-c)\mathrm{}}^n$. The observed variation of $D$ can be approximately reproduced for $n=150\mathrm{}$. (ii) These high-temperature data are also equally well fitted by the Appelbaum-Kondo expression: $\Delta \rho \mathrm{}\left(T\right)=E\{1-(\frac{16cos2{\delta }_{\nu }}{3{cos}^2{\delta }_{\nu }}\left){\left[\right(\frac{T}{T_K}\left)\ln \right(\frac{T}{T_K}\left)\right]}^2\right\}$. The scaling parameter $E$ increases linearly with $c$ and the Kondo temperature $T_K$ is estimated at about 2300 K. Possible variations in the potential phase shift ${\delta }_{\nu }$ indicate that the amount of $s$-band screening may increase as $c$ increases. Further experiments are necessary, however, to determine the eventual applicability of either model. Finally, estimates are made of the Matthiessen's-rule deviations $\Delta \mathrm{}\left(T\right)\mathrm{}$, which are then fitted within the framework of a "parallel conduction" model, in which $\frac{1}{\Delta }\mathrm{}\left(T\right)=\frac{1}{\alpha {\rho }_h}\mathrm{}\left(T\right)+\frac{1}{\beta {\rho }_i}\mathrm{}\left(T\right)\mathrm{}$. ${\rho }_h\mathrm{}\left(T\right)\mathrm{}$ is the host and ${\rho }_i\mathrm{}\left(T\right)\mathrm{}$ the impurity resistivity. A concentration independent value for $\alpha$ of 0.31±0.04 is obtained, but $\beta$ is found to vary with concentration around a value of 0.06.