Surface composition and chemistry of evaporated Permalloy films observed by x−ray photoemission spectroscopy and by Auger electron spectroscopy

Abstract

Auger electron spectroscopy (AES) and x−ray photoemission spectroscopy (XPS) are addressed to the problem of characterizing the air−formed oxide layer on 50−2000−Å−thick Permalloy films. Ar⁺ ion sputter etching is employed to obtain an elemental profile with AES and a chemical profile with XPS. The films were prepared in a vacuum of 5×10⁻⁷ Torr and exposed to the laboratory environment for three weeks. The surface of these unprotected Permalloy films is found to have a composition and chemistry quite different from that of pure Permalloy. For thin films (50 Å) this abnormal region constitutes a sizeable portion of the film. A complex chemisorption layer is observed on top of a 12−Å oxide layer. The Fe−to−Ni ratio in the oxide layer is twice that of the film bulk and the concentration of oxidized Ni falls off faster with depth than that of oxidized Fe. A localized depletion layer of iron, approximately 12 Å thick, is observed between the oxide layer and bulk Permalloy which appears at a depth of 25 Å into the film. These results suggest a consistent although far more complex surface than that implied from previous investigations. The influence of this oxide on the low−temperature ferromagnetic resonance of these films is discussed in the preceding paper.