Fabrication of fully epitaxial magnetic tunnel junctions using full-Heusler alloy Co2Cr0.6Fe0.4Al thin film and MgO tunnel barrier

Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated using a Co-based full-Heusler alloy CO2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier. The fabricated MTJs had the following layer structure: MgO buffer layer/CCFA lower electrode/MgO tunnel barrier/CoFe upper electrode, grown on a MgO single-crystal substrate. All layers were successively deposited in an ultrahigh vacuum chamber through the combined use of magnetron sputtering and electron beam evaporation. RHEED patterns observed in situ for each layer during preparation clearly indicated that all layers grew epitaxially with the (001) basal plane. The microfabricated epitaxial CCFA/MgO/CoFe MTJs demonstrated relatively high tunnel rnagneto-resistance ratios, for MTJs using a full-Heuster alloy, of 42% at room temperature and 74% at 55 K. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure utilizing the potentially high spin polarization of this material system.