Dependence of Giant Magnetoresistance on the Size and Composition of Ferromagnetic 3d Metal Precipitates in a Silver Matrix.

The structure and the giant magnetoresistance (GMR) of granular magnetic alloys are described. A study using epitaxial Ag-Co and Ag-Ni granular alloys films demonstrates that the key influences which affect the magnitude of the GMR are the ferromagnetic precipitate size, concentration, and composition. Subsequent studies are done which isolate these factors. First, the influences of precipitate size and concentration on the GMR of epitaxial granular alloy films consisting of rm Co_{0.4 }Ni_{0.6} precipitates in a Ag matrix are reported. This study verifies that the spin-dependent scattering of the conduction electrons, which is the origin of the GMR, occurs primarily at the precipitate-matrix interface. Second, the influence of the composition of fcc precipitates in an Ag matrix is reported using precipitate alloys of Cu-Ni, Ni-Co, and Co-Fe that had saturation magnetizations (M_ {rm s}) in the range 0-1500 emu/cm ^3. After adjusting the results for the variation in precipitate size with change in composition, the magnetoresistive properties were found to vary approximately linearly with M_{rm s}. Precipitates of Co-Fe at compositions that gave a bcc phase behaved somewhat differently.