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

Heusler Alloys Co₂FeSi and Co₂MnSi were deposited on both single crystal MgO (100) and polycrystalline SiO₂ silicon thermal oxide substrates and characterized by x-ray diffraction before and after thermal annealing at various temperatures. Co₂FeSi and Co₂MnSi deposited on MgO (100) grow as L2₁ or B2 structures but grow as an A2 structure on the SiO₂ substrate. Co₂FeSi and Co₂MnSi 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 Co₂₀Fe₆₀B₂₀ as those layers in the more common MTJ stack. The tunneling magnetoresistance (TMR) ratio is higher if Co₂FeSi is the free layer, but lower when Co₂FeSi is the reference layer.