Spin-glass freezing and RKKY interactions near the metal-insulator transition in amorphous Gd-Si alloys

Magnetization measurements of giant negative magnetoresistive amorphous GdxSi1-x ( 0.04<x<0.19) show strong mixed ferromagnetic and antiferromagnetic interactions and spin-glass freezing. The interactions appear to be an RKKY-like indirect exchange mediated by the conduction electrons, but are strikingly independent of their localization at the metal-insulator (MI) transition, presumably because the localization length exceeds the inter-Gd distance. The susceptibility per Gd atom in the paramagnetic state shows a nontrivial dependence on composition, with a maximum at the MI transition.