First-principle theories predicted an extremely high magnetoresistance (MR) ratio over 1000% in epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs).1,2) This giant tunneling magnetoresistance (TMR) effect originates from a coherent spin-dependent tunneling of highly spin-polarized Δ1 Bloch states. We have fabricated fully epitaxial Fe-Co(001)/MgO(001)/Fe-Co(001) MTJs 3-6) as well as textured CoFeB/MgO(001)/CoFeB MTJs 7,8) and successfully achieved giant MR ratios above 400% at room temperature (RT). An ultra-low tunneling resistance indispensable for magnetic sensor application has also been achieved in the CoFeB/MgO(001)/CoFeB MTJs.9,10) Current-induced magnetization switching, which is a novel writing technology for high-density MRAM, has also been demonstrated using CoFeB/MgO(001)/CoFeB MTJs.11,12) The MgO-based MTJs were also found to be useful for microwave device applications.13) The giant TMR effect in the MgO-based MTJs is the key for next-generation spintronic applications.
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