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 \ifmmode^\circ\else\textdegree\fi{}K. The magnetic susceptibilities of these alloys have also been measured in the range 2.5-300 \ifmmode^\circ\else\textdegree\fi{}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 $\ensuremath{\chi}={\ensuremath{\chi}}_{0}+\frac{C}{(T\ensuremath{-}\ensuremath{\Theta})}$ at low temperatures. For $\mathrm{Pd}\mathrm{Np}$, $\ensuremath{\Theta}\ensuremath{\simeq}\ensuremath{-}13$ \ifmmode^\circ\else\textdegree\fi{}K and ${\ensuremath{\mu}}_{\mathrm{eff}}=2.0\frac{{\ensuremath{\mu}}_{B}}{\mathrm{Np}}$ atom. For $\mathrm{Pd}\mathrm{Pu}$, $\ensuremath{\Theta}\ensuremath{\simeq}\ensuremath{-}{3}^{\ensuremath{\circ}}\mathrm{K}$ and ${\ensuremath{\mu}}_{\mathrm{eff}}$ increases from 0.55 to 1.3 $\frac{{\ensuremath{\mu}}_{B}}{\mathrm{Pu}}$ 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 ${T}_{K}\ensuremath{\simeq}{15}^{\ensuremath{\circ}}\mathrm{K}$. The $\mathrm{Pd}\mathrm{Pu}$ system is discussed in terms of localized spin fluctuations of the $5f$ electrons, with a spin-fluctuation temperature ${T}_{S}\ensuremath{\simeq}{1}^{\ensuremath{\circ}}\mathrm{K}$. 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.