エピタキシャル Fe/MgAl2O4/Fe(001)強磁性トンネル接合における結晶性と伝導特性

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We investigated in detail the crystallinity and transport properties of fully epitaxial Fe(001)/spinel MgAl2O4(001)/Fe(001) magnetic tunnel junctions (MTJs). We found that high (001) orientation (< 0.20°) and an extremely flat surface (averaged roughness ∼ 0.09 nm) were achieved in the optimized Fe/MgAl2O4/Fe MTJs exhibiting tunnel magnetoresistance (TMR) of more than 100% as well as excellent bias-voltage dependence. The misfit dislocation density of the MgAl2O4/Fe interface was determined to be precisely 5 × 10-2 nm-1. In addition, post-annealing in the preparation process has a significant influence on TMR and its bias-voltage dependence in Fe/MgAl2O4/Fe MTJs, suggesting that the crystallinity of the MgAl2O4 barrier interfaces was effectively improved by postannealing of each layer. The results provided useful information for understanding and developing epitaxial MTJs with coherent tunneling.