DEPENDENCE OF GIANT MAGNETORESISTANCE ON THE NUMBER OF VALENCE-ELECTRONS IN THE FERROMAGNETIC CONSTITUENT OF GRANULAR ALLOYS - PRECIPITATES OF FACE-CENTERED-CUBIC FE-CO, CO-NI, AND NI-CU ALLOYS IN AG MATRICES

The dependence of giant magnetoresistance on the composition of ferromagnetic face-centered cubic precipitates in an Ag matrix grown epitaxially on MgO {100} is described. These compositions were chosen from the alloy ranges Ni0.6Cu0.4→Ni→NixCo 1-x→ Co→Fe0.2Co0.8 to give a number of valence electrons per atom, n=n3d+n4s, in the ferromagnetic precipitates that ranged from 8.8 to 10.4. This corresponds to a decrease of the saturation magnetization from ∼1500 emu/cm3 to approximately zero. To reduce the influence of other variables the concentration of the precipitates was kept constant (at 23.5 vol %) and their size approximately so. Corrections are applied to adjust for some remaining variation in precipitate size. With other factors held constant, there is a steady increase in both the magnetoresistance ratio and the magnetic-field-dependent resistivity with increase in the saturation magnetization of the alloys, i.e., with increase in the spontaneous magnetization of the single-domain precipitates. © 1995 American Institute of Physics.