Magnetoresistance studies of melt-spun amorphous Fe1−<i>x</i>Zr<i>x</i> ferromagnets

Abstract

A remarkable feature in amorphous Fe1−xZrx alloys is that for Fe concentrations greater than 90 at %, the ferromagnetic transition temperature TC decreases with increasing Fe concentration. In addition, alloys containing 93–90 at % Fe are found to show a spin-glass-like behavior at low temperatures, i.e., below TC. The electrical resistivity of these alloys shows a minimum at roughly the Curie temperature. We have measured the transverse magnetoresistance of Fe91Zr9, and Fe90Zr10 alloys from 4 to 300 K in applied magnetic fields as large as 9 T. We find that (1) the field derivative of the magnetoresistance is positive at all temperatures in applied fields larger than 0.1 T; (2) a maximum occurs in the magnetoresistance at roughly the Curie temperature; (3) below the Curie temperature a small negative low-field magnetoresistance develops which increases with decreasing temperature. These results indicate that the resistance minimum which occurs around the Curie temperature for these alloys is due to the coherent exchange scattering by the Fe moments, and is not associated with a Kondo mechanism as previously proposed.