Coherent spin-dependent tunneling in magnetic tunnel junctions with MgO(001) tunnel barrier

A fully epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions were fabricated using electron beam evaporation under ultrahigh vacuum and achieved a giant tunneling magnetoresistance (TMR) effect over 180% at room temperature. The magnetoresistance (MR) ratio for the crystalline MgO(001) tunnel barrier is about three times that for the amorphous Al-O barrier indicating an importance of the crystalline symmetry of tunnel barrier for the coherent tunneling of Δ₁ electrons. The MTJs with crystalline MgO(001) tunnel barrier also have high thermal stability and reproducibility of TMR. An oscillation of the TMR effect was also observed as a function of the thickness of MgO tunnel barrier, which could be a direct evidence of coherent spin-dependent tunneling. Such conservation of the coherency of spin polarized electron across the tunnel barrier will enable us to develop a variety of novel spintronics devices with quantum mechanical functions.