Effect of Pressure on the Low-Temperature Electrical Resistance of Pure Pd and Very Dilute Pd: Ni Alloys

Measurements of the low-temperature electrical resistivity of pure Pd and a series of very dilute Pd: Ni alloys (0.32-, 0.55-, and 1.0-at.% Ni) have been carried out under hydrostatic pressure (∼4.5 kbar) using solid helium as the pressure medium. It has been found that the coefficient of the $T^2$ contribution believed to arise from paramagnon-enhanced electron-electron scattering is reduced upon application of pressure for each alloy by an amount greater than that estimated on the basis of a localized-exchange-enhancement model coupled with earlier magnetostriction work. The dependence of this effect on the concentration of Ni is compared with the prediction of a localized-exchange-enhancement model. The results are consistent with the idea that electron-paramagnon scattering gives rise to a negative deviation from $T^2$ behavior—of order greater than $T^2$ and less than $T^5$—in the alloys which is more strongly reduced in size upon application of pressure than is the $T^2$ contribution itself. For the alloy containing 1-at.% Ni both the zero-pressure data and the pressure data indicate that a description of the temperature-dependent resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ for $T<\mathrm{}10\mathrm{}°$K by $\rho ={\rho }_0+A{T}^2+B{T}^5$, as has previously been suggested, is inadequate. A large reversible decrease in the residual resistivity of each of the alloys was observed upon application of pressure. The relative size of this effect is four times as large as the relative volume change. This suggests that there may be a significant transfer of low-mobility $d$ electrons to high-mobility $s$ states with application of pressure. A simple model is offered to explain the role of Ni in this effect.