The dependence of nano-contact magnetoresistance on the bulk scattering spin asymmetry in CoFe alloys with oxidation impurities

Nano-contact magnetoresistance (NCMR) spin-valves (SVs) using an AlOx nano-oxide-layer (NOL) have numerous nanocontacts in the thin AlOx oxide layer. The NCMR theoretically depends on the bulk scattering spin asymmetry (beta) of the ferromagnetic material in the nanocontacts. To determine the relationship between NCMR and beta, we investigated the dependence of NCMR on the composition of the ferromagnetic material Co1-xFex. The samples were annealed at 270 degrees C and 380 degrees C to enhance the MR ratio. For both annealing temperatures, the magnctorsistance ratio in the low-resistance area product region at less than 1 Omega mu m(2) was maximized for Co0.5Fe0.5. To evaluate beta exactly, we fabricated current-perpendicular-to-plane giant magnetoresistance SVs with Co1-xFex/Cu/Co1-xFex layers and used Valet and Fert's theory to solve the diffusion equation of the spin accumulation for a ferromagnetic layer/non-ferromagnetic layer of five layers with a finite diffusion length. The evaluated beta for Co1-xFex was also maximized for Co0.5Fe0.5. Additionally, to determine the difference between the experimental MR ratio of NCMR SVs and the theoretical MR ratio, we fabricated Co0.5Fe0.5 with oxygen impurities and estimated the decrease in beta with increasing oxygen impurity concentration. Our Co0.5Fe0.5 nanocontacts fabricated using ion-assisted oxidation may contain oxygen impurities, and the oxygen impurities might cause a decrease in beta and the MR ratio. (C) 2015 AIP Publishing LLC,