Abstract
We report enhanced tunnel magnetoresistance (TMR) ratios of 188$%$ (308$%$) at room temperature and 328$%$ (479$%$) at 15 K for cation-site-disordered MgAl${}_{2}$O${}_{4}$-barrier magnetic tunnel junctions (MTJs) with Fe (Fe${}_{0.5}$Co${}_{0.5}$ alloy) electrodes, which exceed the TMR ratios theoretically calculated and experimentally observed for ordered spinel barriers. The enhancement of TMR ratios is attributed to the suppression of the so-called band-folding effect in ordered spinel MTJs [Phys. Rev. B 86, 024426 (2012)]. First-principles calculations describe a dominant role of the oxygen sublattice for spin-dependent coherent tunneling, suggesting a mechanism of coherent tunneling occurring even in the disordered systems.
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