Hall effect in amorphous thin-film magnetic alloys

Abstract

Amorphous magnetic alloys have unusually large extraordinary Hall coefficients (Rs) defined by the ratio of the Hall resistivity to the net magnetic moment of the alloy. We have studied the Hall effect in amorphous films in the ternary ferrimagnetic systems Co-Gd-Mo and Co-Gd-Au, alloys which exhibit compensation temperatures (Tcomp). Above Tcomp the Hall coefficient Rs is positive and below Tcomp the sign of Rs changes to negative in a discontinuous manner, probably limited by the homogeneity of the sample. We have also prepared amorphous Gd-Au and Y-Co films and measured Rs which we use to qualitatively separate the effects of the Co and Gd sublattices in the ternary alloys. We attribute the sign of Rs to a combined effect of a negative Gd and a positive Co Hall coefficient. Above Tcomp the Co is dominant and points in the direction of the applied field H while Gd is antiparallel to H. Thus, both sublattices contribute in a positive sense to Rs. Below T comp the Gd moment is dominant and the sign of Rs is reversed for both sublattices. Values of Rs up to 25×10 -9 Ω cm/G are measured near Tcomp and when Mo is present Rs is reduced to 5×10-9 Ω cm/G. Molybdenum is known to cause a strong decrease in the moment of the cobalt sublattice and this probably is the reason Rs decreases. Our interpretation of the Hall effect in these ferrimagnetic systems differs from other recently proposed models.