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

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(Al_0.5 Si_0.5) 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(Al_0.5 Si_0.5) 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 (Cr_0.1 Fe_0.9 )Si, Co₂ Mn(Ga_0.5 Sn_0.5 ), and Co₂ Fe(Ge_0.5 Ga_0.5) alloy thin films were investigated for CPP-GMR SVs. Among them, the Co₂Fe(Ge_0.5Ga_0.5) alloy showed a high CPP-GMR ratio in the pseudo SVs exceeding 40% at RT and 120% at 10 K.