To measure the bio magnetic field from the heart and brain at room temperature, the magnetic tunnel junctions (MTJs) based sensor is required to achieve a high sensitivity which is defined as the TMR ratio/2Hk (where Hk is anisotropic magnetic field of the free layer). To realize both high TMR ratio and small Hk, we employed (001)-oriented polycrystalline Co-based Heusler alloy material (Co2Fe0.4Mn0.6Si) for the free layer which is known for its high spin polarization and small Hk. In this study, we optimized the crystal and magnetic properties of Co2Fe0.4Mn0.6Si free layer and succeeded in reducing Hk in polycrystalline CFMS free layer with high B2 ordering. We also demonstrated the linear output of TMR in MTJs fabricated under the optimized condition.
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