Fcc-bcc phase transition of epitaxial (111)-Fe films: a structural and magnetic study

Epitaxial Cu/Fe/Cu trilayers with Fe film thickness between 4 and 110A° have been deposited on the 7×7 reconstructed surface of Si(111) single crystal. The structural and chemical characterization of Fe films was accomplished by in situ low energy electron diffraction, Kikuchi electron diffraction and Auger electron spectroscopy. As the Fe thickness exceeds about 6-8A° , a fcc-bcc phase transition occurs by the appearance of bcc(110) domains in the Kurdjumov-Sachs orientation. The structural transformation is also confirmed by ex situ X-ray diffraction experiments in the h-2h configuration. The evolution of the magnetic properties with the Fe film thickness has been studied by means of surface magneto-optic Kerr effect. Hysteresis loops measurements in the longitudinal configuration show a marked increase of the saturation signal which can be associated with the structural fcc-bcc phase transition of Fe.