5fMagnetism in Palladium-Actinide Solid Solutions

Abstract

The electrical resistivities of palladium alloys containing 2.0 at.% or less neptunium or plutonium have been measured in the range 1.3-300 °K. The magnetic susceptibilities of these alloys have also been measured in the range 2.5-300 °K. Resistivity minima are observed for the $\mathrm{Pd}\mathrm{Np}$ alloys, but the resistivities of the $\mathrm{Pd}\mathrm{Pu}$ alloys have positive slopes at low temperatures. The magnetic susceptibilities of the alloys can be fitted to $\chi ={\chi }_0+\frac{C}{(T-\Theta )}$ at low temperatures. For $\mathrm{Pd}\mathrm{Np}$, $\Theta \simeq -13\mathrm{}$ °K and ${\mu }_{\mathrm{eff}}=2.0\mathrm{}\frac{{\mu }_B}{\mathrm{Np}}$ atom. For $\mathrm{Pd}\mathrm{Pu}$, $\Theta \simeq -3^{\circ }\mathrm{K}$ and ${\mu }_{\mathrm{eff}}$ increases from 0.55 to 1.3 $\frac{{\mu }_B}{\mathrm{Pu}}$ atom with decreasing plutonium concentration. Apparently the $5f$ level is sufficiently localized to form a magnetic moment in $\mathrm{Pd}\mathrm{Np}$, and is spin compensated at low temperatures. The Kondo temperature is estimated to be $T_K\simeq {15}^{\circ }\mathrm{K}$. The $\mathrm{Pd}\mathrm{Pu}$ system is discussed in terms of localized spin fluctuations of the $5f$ electrons, with a spin-fluctuation temperature $T_S\simeq 1^{\circ }\mathrm{K}$. The $\mathrm{Pd}\mathrm{U}$ system was discussed earlier. It is suggested that in these alloys, indirect interactions between uranium impurities via the palladium conduction electrons and the modification of the $4d$ subband in the vicinity of uranium atoms cause the $5f$ level to narrow and lower to the Fermi level.