Observation of isotropic giant magnetoresistance in paramagnetic Au80Fe20 - art. no. 180404

Magnetization and magnetoresistance were measured at room temperature and a bove on Au80Fe20 platelets and ribbons obtained by solid-state quenching an d melt spinning, The as-quenched samples contain a solid solution of Fe in Au and exhibit a paramagnetic (Curie-Weiss) behavior in the considered temp erature range; magnetic data indicate very short-ranged magnetic correlatio n among adjacent spins, enhanced by local composition fluctuations. The sol id solution is very stable. Only a very limited fraction (never exceeding 1 %) of nanometer-sized, bce Fe particles appears after lone-time isothermal anneals at suitable temperatures. A negative magnetoresistance was observed at room temperature in ail examined sample. The observed effect is anhyste retic, isotropic, and quadratically dependent on magnetic field H and magne tization M. The signal scales with M rather than with H, indicating that it depends on the field-induced magnetic order of the Fe moments, as it does for conventional giant magnetoresistance in granular magnetic systems. This effect derives from spin-dependent scattering of conduction electrons from single Fe spins or very small Fe clusters. The scattering centers are almo st uncorrelated at a distance of the order of the electronic mean free path (of the order of 1.5 nm, or a few atomic spacings, at RT).