L10 ordering at different stages of Fe0.5Pd0.5 epitaxial growth

FePd layers deposited by molecular beam epitaxy at 620 K on a (001) Pd buffer are investigated. At this growth temperature, an L1(0) structure is expected; we compare the crystal ordering at different depths in these thin films. Fe-57 is used as a local probe at an atomic scale, located at different places within an equimolar FePd layer. The relationship between the alloy structure and the magnetic anisotropy of the films is investigated by Mossbauer spectroscopy. The possible decrease of the L1(0) ordering during growth is not observed. On the contrary, the quality of the L1(0) structure seems to improve, as confirmed by the low number of near-neighbors for iron atoms located on the top level of the alloy layer. Iron-rich clusters shaping into large vertical defects across the whole alloy layer are also observed; these clusters correspond to chemically disordered areas within the film. At the buffer interface, disordered, and dilute iron alloys (mean composition: Fe-0.25 Pd-0.75) with in-plane momenta are identified and explained assuming iron atom diffusion through about 1 nm thick Pd buffer, due to Pd segregation. Some iron rich aggregates could be the consequence of iron homocoordination or Pd surface segregation. The L1(0) structure is assumed to occur after about 1.7 nm alloy deposit. (C) 2002 American Institute of Physics.