γ-FeMn/NiFe 2層膜の磁気交換結合に及ぼす酸化の影響

抄録

The Effect of surface oxidation at the interface between Ni-Fe and Fe-Mn alloy thin layers on the exchange coupling of an Fe-Mn/Ni-Fe bilayer thin film was investigated. The Ni₈₂-Fe₁₈ alloy film was deposited by an electron beam system in a vacuum of 10⁻⁴ Pa. The deposited film was exposed to air for 72 h in order to oxidize the surface of the Ni-Fe layer. The surface of the Ni-Fe layer was etched by ion-milling to clean the oxidized surface. The Fe-Mn alloy film was deposited by ion beam sputtering, using a Fe₅₀Mn₅₀ target. The exchange coupling field was obtained from the shift in the B-H loop. The following can be concluded from the results. Exchange coupling does not occur, when the Ni-Fe surface is oxidized, due to the growth of paramagnetic α-(Fe-Mn). However, if the Fe-Mn film is deposited immediately after etching the Ni-Fe surface, exchange coupling is observed. This is due to the epitaxial growth of antiferromagnetic γ-(Fe-Mn) on the clean surface. The exchange coupling field is comparable to the value for the Ni-Fe/Fe-Mn multilayer deposited continuously. The exchange coupling field becomes smaller when the Fe-Mn layer is thinner than 10 nm, because Mn is preferentially oxidized.