There is considerable interest in understanding the surface oxidation reactions of transition-metal alloys with potentially useful magnetic properties. These reactions can either lead to passivation or corrosion of the magnetic film under normal atmospheric conditions. Little is known, however, about the surface oxidation reactions of MnFe. In the present study, thin films of MnFe prepared by dc magnetron sputter deposition onto Si, Cu, and Ni8()Fe20have been characterized magnetically by superconducting quantum interference device (SQUID) and vibrating sample magnetometer measurements and their surface chemistry has been followed by angle resolved x-ray photoelectron spectroscopy and ellipsometry. The reactivity of the clean MnFe surface with O2, H2O, and N2was investigated. The interaction of MnFe with O2proceeds by preferential oxidation and surface segregation of Mn oxide. The final products of oxidation after a 66 000-L exposure are MnO and Fe2O3, in agreement with thermodynamic considerations. Compared to the reactivity of O2with MnFe, the adsorption of H2O on MnFe is extremely sluggish, while N2does not adsorb at all. The controlled oxidation behavior of MnFe is compared and contrasted to that observed for the related alloy NiFe and to that observed in air oxidation of both these alloys. © 1988, American Vacuum Society. All rights reserved.