Effect of Gas Adsorption onto the Interface on the Exchange-Coupling Field of Ni-Fe/25 at%Ni-Mn Film

Abstract

The effect of gas adsorption onto the interface on the exchange-coupling field of Ni-Fe/25 at%Ni-Mn film was investigated. Ni-Fe/25 at%Ni-Mn/Ni-Fe trilayer films were prepared on an Si(100) substrate by a facing-targets sputtering method. The lower interface of trilayer films was exposed for 1 hour in various atmospheres controlled by introducing air or N2 through a variable leak valve. The strength of the exchange coupling, Jk, decreased rapidly when the air pressure during exposure exceeded 1×10-7 Torr. From the temperature dependence of Jk and cross-sectional TEM observation, it was found that γ-Ni-Mn became easy to separate into α-Mn+θ-NiMn with increasing air pressure, leading to the decrease in Jk at R.T. This structural change in Ni-Mn layer was considered to be caused by the H2O/O2 gas adsorption or partial oxidation on the lower Ni-Fe surface, preventing epitaxial growth of γ-Ni-Mn grain on it.