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Perfectly lattice-matched magnetic tunnel junctions (MTJs) consisting of a Heusler alloy B2-Co 2 FeAl (CFA) electrode and a cation-disorder spinel (Mg-Al-O) barrier were fabricated by sputtering and plasma oxidation. We achieved a large tunnel magnetoresistance (TMR) ratio of 228% at room temperature (RT)(398% at 5 K) for the epitaxial CFA/MgAl-O/CoFe (001) MTJ, in which the effect of lattice defects on TMR ratios is excluded. With inserting a ultrathin (≤ 1.5 nm) CoFe layer between the CFA and Mg-Al-O, the TMR ratio further increased up to 280% at RT (453% at 5 K), which reflected the importance of controlling barrier-electrode interface states other than the lattice matching.

Cobalt-based Heusler alloys with an L2 1 structure have received substantial attention due to their great potential for spintronics applications since some of them show a perfectly spin-polarized band structure (so-called half-metals 1), a …