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

Abstract

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.