Temperature dependence of magnetoresistive output of pseudo spin valves with Co₂Fe(Al_1-xSi_x) Heusler alloys and a Ag spacer

We investigated the temperature dependence of magnetoresistive (MR) outputs of current-perpendicular-to-plane pseudo spin valves with Co ₂FeAl_1-xSi_x (0 ≤ x ≤ 1) Heusler alloy ferromagnetic layers and a Ag spacer layer to optimize x. The MR ratios at room temperature do not show x dependence, while the MR ratios measured at 5 K showed strong x dependence; the largest resistance change-area product ΔRA = 21 mΩ·μm² was obtained for x = 1 and ΔRA decreased with decreasing x. The results apparently contradicts with the theoretical prediction that the highest spin polarization is attained for x = 0.5. The discrepancy is due to the structural origin that the L2 ₁ order is obtained only in the Co₂FeSi alloy film.