Large magnetoresistance anisotropy in a new class of amorphous ferromagnets: U_100-x-ySb_xMn_y

Abstract

U100-x-ySbxMny amorphous ferromagnets were prepared that have an anisotropic magnetoresistance (AMR) as high as 9.3% at 15 K and a 2-T field. This is a striking result, since the AMR of typical amorphous ferromagnets does not exceed 1%. These materials are random anisotropy ferromagnets, with large coercive fields (Hc =1.2 T, 15 K) following a thermally activated regime at low temperature. The Curie temperatures range from 95 to 112 K. Resistivity values vary from 200 to 400 μΩ cm and the Hall angle can reach 20°at 15 K. For T>TC, the resistivity follows a field-independent ln T behavior with dρ/dT showing a sharp anomaly at TC. Below TC, both these quantities are strongly anisotropic, depending on the angle between the magnetization and the current. Magnetization reversal process are inferred from the magnetoresistance hysteresis cycles - both coherent rotation and 180°domain-wall motion occur.