Polycrystalline Co2Fe0.4Mn0.6Si Heusler alloy thin films with high B2 ordering and small magnetic anisotropy for magnetic tunnel junction based sensors

摘要

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/2 H subk/sub (where H subk/sub is anisotropic magnetic field of the free layer). To realize both high TMR ratio and small H subk/sub, we employed (001)-oriented polycrystalline Co-based Heusler alloy material (Cosub2/subFesub0.4/subMnsub0.6/subSi) for the free layer which is known for its high spin polarization and small H subk/sub. In this study, we optimized the crystal and magnetic properties of Cosub2/subFesub0.4/subMnsub0.6/subSi free layer and succeeded in reducing H subk/sub in polycrystalline CFMS free layer with high B2 ordering. We also demonstrated the linear output of TMR in MTJs fabricated under the optimized condition.