Highly Spin-Polarized Tunneling in Epitaxial Magnetic Tunnel Junctions with a Co2MnSi Electrode and a MgO Barrier with Improved Interfacial Structural Properties

Fully epitaxial magnetic tunnel junctions (MTJs) with a Heusler alloy Co2MnSi electrode and a MgO barrier were prepared on MgO-buffered MgO(001) substrates with various layer structures to elucidate the contribution of coherent tunneling to the spin-dependent tunneling characteristics of these MTJs, which potentially feature both the half-metallicity of Co2MnSi and coherent tunneling. MTJs consisting of (from the lower side) Co50Fe50 (CoFe)/MgO/Co2MnSi or CoFe-buffered Co2MnSi/MgO/CoFe showed almost identical, high tunnel magnetoresistance (TMR) ratios of 335% at 290 K (1049% at 4.2 K) and 340% at 290K (879% at 4.2 K), respectively. In contrast, MTJs consisting of MgO-buffered Co2MnSi/MgO/CoFe showed a lower TMR ratio of 173% at 290 K (448% at 4.2 K). The higher TMR ratios obtained for CoFe/MgO/Co2MnSi MTJs and CoFe-buffered Co2MnSi/MgO/CoFe MTJs can be ascribed to the enhanced contribution of coherent tunneling that originated from decreased misfit dislocation densities at the lower and upper interfaces with a MgO barrier. (C) 2012 The Japan Society of Applied Physics