Surface-oxidation-induced phase separation in FeMn thin films

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Abstract
Films of Fe50Mn50, 700 Å thick, were deposited on glass substrates by diode rf sputtering. Auger electron spectroscopy, and x-ray fluorescence analysis verified the film composition and x-ray diffraction determined the crystalline phase to be α-Mn(Fe), a complex bcc-like structure and a considerable deviation from that dictated by the equilibrium binary phase diagram. The films were annealed for 1 h at 260 °C and 10−7, 10−5, and 10−2 Torr. Auger depth profile analysis showed that (a) while no further oxidation (than that induced by ambient exposure) occurred during annealing at the lowest pressure, severe film oxidation took place at the highest pressure and (b) preferential surface oxidation of Mn resulted in a layered structure consisting of a surface Mn- and oxygen-rich layer followed by a region (deeper into the film) depleted in Mn and Fe enriched. The crystalline phases present were determined by x-ray diffraction analysis to be MnO (fcc) and α-Fe(Mn) (bcc). Magnetic measurements of the oxidized films revealed that they displayed in-plane isotropic ferromagnetic properties, with 4πMs∼15–18 kG for the most extensively oxidized films.