Bias-voltage dependence of tunnel magnetoresistance depending on the crystal structure of bottom ferromagnetic electrode

Two kinds of MTJs were prepared using magnetron sputtering: a conventional polycrystalline MTJ with multilayer structure of Si(100)/SiO₂/Ta 5 nm/NiFe 3 nm/Cu 20 nm/NiFe 3 nm/IrMn 10 nm/CoFe 40 nm/Al 1.6 nm-O/CoFe 4 nm/NiFe 20 nm/Ta 5 nm and a semi-epitaxial MTJ with a multilayer structures of Al₂O₃ (0001)/Pt (111) 20 nm/NiFe (111) 50 nm/Al 1.6 nm-O/CoFe 4 nm/IrMn 10 nm/NiFe 30 nm. The effect of the state of a ferromagnet/insulator interface on the bias-voltage dependence of TMR was investigated. It was found that the more crystal structure of bottom FM electrode improves, the more plasma oxidation proceeds uniformly and V₊₁2/ (bottom interface) increases. V_-12/ (top interface), on the other hand, are similar regardless of crystal structure of the bottom FM electrode.