STRUCTURE AND CHEMICAL ORDER IN SPUTTERED EPITAXIAL FEPD(001) ALLOYS

We report the structure and chemical ordering in sputtered FePd(0 0 1) alloys with varying growth temperature and Pt buffer-layer thickness. Increasing the thickness of the Pt buffer layer induces a transition from growth of a cubic chemically disordered FePd phase to a tetragona lly distorted chemically ordered alloy. This behavior correlates with the buffer-layer morphology, which is discontinuous for films thinner than 100 Angstrom, but becomes more uniform for Pt thicknesses above 1 50 Angstrom. Two distinct regimes are observed when varying the growth temperature. For temperatures 300 degrees C and below, there is no si gn of chemical order, either along the surface normal or in the film p lane, while for 400 degrees C and above, chemical ordering. increases linearly with the growth temperature. This behavior is in contrast to the growth temperature dependence observed in MBE grown FePt alloys, w here long-range chemical order varies continuously with growth tempera ture. We explain this difference as due to different film growth mecha nisms. (C) 1998 Elsevier Science B.V. All rights reserved.