S−dExchange Interaction in Amorphous Cr-Pd-Si and Mn-Pd-Si Alloys

Abstract

The electrical and magnetic properties of amorphous alloys obtained by rapid quenching from the liquid state have been studied. The compositions of these alloys are ${\mathrm{Cr}}_{x}{\mathrm{Pd}}_{80\ensuremath{-}x}{\mathrm{Si}}_{20}$ and ${\mathrm{Mn}}_{x}{\mathrm{Pd}}_{80\ensuremath{-}x}{\mathrm{Si}}_{20}$, in which $x$ is the atomic concentration and ranges between 0 and 7. A well-defined minimum in the resistivity versus temperature is observed for these alloys except for the case where $x=0$. Below the resistivity-minimum temperature ${T}_{m}$, the resistivity difference $\ensuremath{\Delta}\ensuremath{\rho}$ varies as -$\mathrm{ln}T$ in agreement with Kondo's theory, and tends to level off at lower temperatures. The resistivity-minimum phenomenon persists in amorphous alloys containing as much as 7 at.% or more of transition metals like Cr or Mn. Also, the resistivity-minimum temperature for some of the amorphous alloys studied can be as high as 580\ifmmode^\circ\else\textdegree\fi{}K. The resistivity-minimum anomaly is always accompanied by a negative magneto-resistivity approximately proportional to the square of the magnetization and a susceptibility obeying the Curie-Weiss law for a wide temperature range. These observations lead to the conclusion that a Kondo-type $s\ensuremath{-}d$ exchange interaction exists in the amorphous Pd-Si alloys containing Cr or Mn. In terms of the $s\ensuremath{-}d$ exchange model, the following statements can be made: (a) The results of susceptibility and magnetoresistivity measurements suggest that the $d\ensuremath{-}d$ spin correlation between magnetic atoms is, in general, weaker in the amorphous alloys than in the corresponding crystalline alloys. This is consistent with the fact that a Kondo-type resistivity anomaly has been observed in amorphous alloys containing 7 at.% Cr or Mn. (b) The spin-compensated state has been observed in the amorphous alloys containing Cr. From the resistivity data, it is concluded that the Kondo temperature of these alloys depends linearly on the Cr concentration. For the Mn-Pd-Si alloys, the spin-compensated state is masked by the $d\ensuremath{-}d$ spin correlation. (c) The $s\ensuremath{-}d$ exchange integrals for the Cr and Mn amorphous alloys are estimated and found to be consistent with Friedel's virtual-bound-state model.