Structure and chemical order in sputtered epitaxial FePd(0 0 1) 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 tetragonally 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 150 Angstrom. Two distinct regimes are observed when varying the growth temperature. For temperatures 300 degrees C and below, there is no sign of chemical order, either along the surface normal or in the film plane, 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, where long-range chemical order varies continuously with growth temperature. We explain this difference as due to different film growth mechanisms. (C) 1998 Elsevier Science B.V. All rights reserved.