We have fabricated MgO-based magnetic tunnel junctions (MTJs) with the CoFeB bottom electrode and top electrodes of poly crystalline Co2FeSi and Co2MnSi Heusler alloys. We have measured temperature dependence of the TMR ratio and TMR-V characteristics at 6 K. We have achieved a high TMR ratio of 90% at RT for the MTJ with Co2FeSi electrode after annealing at 325° C. The MTJ with Co2MnSi electrode showed a significant annealing temperature dependence of the TMR ratio. The increase of TMR ratio by annealing is due to the crystallization of the Co2MnSi Heusler layer. Furthermore, the strong temperature dependence of TMR ratio and the anomalous TMR-V characteristics have been observed in the MTJ with Co2MnSi.
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