The positive Hall coefficients of amorphous transition-metal alloys

Abstract

Experimental results are presented for the Hall coefficients of a number of amorphous Cu-Zr, Cu-Ti and Cu-Hf alloys in the temperature range 4.2-270K. With the exception of Cu₉₂Zr₈, all these alloys are found to have positive Hall coefficients and none show any significant temperature dependence. The fact that R_H is temperature independent can probably be understood as a direct consequence of the isotropic nature of the scattering. The positive values cannot be understood on the basis of nearly free electron ideas nor within the random phase model if hybridisation is neglected. It is therefore argued that the positive values are probably due to the s-d hybridisation leading to negative group velocities at the Fermi level. Using this approach a qualitative account can be made of the compositional dependence of R_H in the alloys used here and in a number of related systems.