Use of Half Metallic Heusler Alloys in CoFeB/MgO/Heusler Alloy Tunnel Junctions

Heusler Alloys Co<sub>2</sub>FeSi and Co<sub>2</sub>MnSi were deposited on both single crystal MgO (100) and polycrystalline SiO<sub>2</sub> silicon thermal oxide substrates and characterized by x-ray diffraction before and after thermal annealing at various temperatures. Co<sub>2</sub>FeSi and Co<sub>2</sub>MnSi deposited on MgO (100) grow as L2<sub>1</sub> or B2 structures but grow as an A2 structure on the SiO<sub>2</sub> substrate. Co<sub>2</sub>FeSi and Co<sub>2</sub>MnSi were also deposited in a magnetic tunnel junction (MTJ) stack as the free and reference layers above and below the MgO barrier layer respectively, thereby replacing Co<sub>20</sub>Fe<sub>60</sub>B<sub>20</sub> as those layers in the more common MTJ stack. The tunneling magnetoresistance (TMR) ratio is higher if Co<sub>2</sub>FeSi is the free layer, but lower when Co<sub>2</sub>FeSi is the reference layer.

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