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

Yohei Shiokawa; JinWon Jung; Takahiko Otsuka; Masashi Sahashi

doi:10.1063/1.4927842

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

J Appl Phys. 2015 Aug 7;118(5):053909. doi: 10.1063/1.4927842. Epub 2015 Aug 5.

Authors

Yohei Shiokawa¹, JinWon Jung¹, Takahiko Otsuka¹, Masashi Sahashi¹

Affiliation

¹ Department of Electronic Engineering, Tohoku University , Aza-Aoba 6-6-05, Aramaki, Aobaku, Sendai 980-8579, Japan.

Abstract

Nano-contact magnetoresistance (NCMR) spin-valves (SVs) using an AlO _x nano-oxide-layer (NOL) have numerous nanocontacts in the thin AlO_x oxide layer. The NCMR theoretically depends on the bulk scattering spin asymmetry ([Formula: see text]) of the ferromagnetic material in the nanocontacts. To determine the relationship between NCMR and [Formula: see text], we investigated the dependence of NCMR on the composition of the ferromagnetic material Co_1-xFe_x. The samples were annealed at 270 °C and 380 °C to enhance the MR ratio. For both annealing temperatures, the magnetorsistance ratio in the low-resistance area product region at less than 1 Ω μm² was maximized for Co_0.5Fe_0.5. To evaluate [Formula: see text] exactly, we fabricated current-perpendicular-to-plane giant magnetoresistance SVs with Co_1-xFe_x/Cu/Co_1-xFe_x 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 [Formula: see text] for Co_1-xFe_x was also maximized for Co_0.5Fe_0.5. Additionally, to determine the difference between the experimental MR ratio of NCMR SVs and the theoretical MR ratio, we fabricated Co_0.5Fe_0.5 with oxygen impurities and estimated the decrease in [Formula: see text] with increasing oxygen impurity concentration. Our Co_0.5Fe_0.5 nano-contacts fabricated using ion-assisted oxidation may contain oxygen impurities, and the oxygen impurities might cause a decrease in [Formula: see text] and the MR ratio.