Co-Based Heusler Alloys for CPP-GMR Spin-Valves With Large Magnetoresistive Outputs

Abstract

We studied various Heusler alloy compositions for the ferromagnetic layers of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin-valves (SVs) to obtain large MR outputs for the read sensor applications. The exchange biased SV with Co2 Fe(Al0.5 Si0.5) alloy showed a resistance change-area product (ΔRA) of 6 m Ωμm2 and an MR ratio of 21% at room temperature when the Co2 Fe(Al0.5 Si0.5) layer was well-B2-ordered by a high temperature annealing at 500°C. The critical bias current density for the spin torque effect on the reduction of ΔRA was ~ 3 × 107 A/cm2. Based on the high spin polarization directly measured by the point contact Andreev reflection method, Co2 (Cr0.1 Fe0.9 )Si, Co2 Mn(Ga0.5 Sn0.5 ), and Co2 Fe(Ge0.5 Ga0.5) alloy thin films were investigated for CPP-GMR SVs. Among them, the Co2Fe(Ge0.5Ga0.5) alloy showed a high CPP-GMR ratio in the pseudo SVs exceeding 40% at RT and 120% at 10 K.