Fe growth on (0001) hcp Ru and (111) fcc Ir: Consequences for structural and magnetic properties

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Abstract
Fe epitaxial growth on hexagonal Ir or Ru lattices by molecular-beam epitaxy is studied with use of in situ electron diffraction and x-ray diffraction. The growth is two dimensional and pseudomorphic up to critical thicknesses for both Ir and Ru lattices. However, reflection high-energy electron diffraction oscillations depend strongly on the crystallographic direction. Above the pseudomorphic regime, additional surface structures appear, which are clearly explained by the occurrence of a Kurdjumov-Sachs growth of (110) bcc plane on (111) fcc or (0001) hcp ones. The evolution of the interatomic distances in the plane of growth with the number of deposited Fe layers is precisely measured with use of electron diffraction and shows that deposited layers slowly relax to the unstrained bcc Fe phase. Macroscopic magnetic measurements on Fe/Ir (111) superlattices demonstrate that the Fe layers have one nonmagnetic phase and one Fe high-moment ferromagnetic phase. The differences between ‘‘free’’ and recovered Fe film on the one hand and between Fe structures in Fe/Ru and Fe/Ir superlattices, on the other hand, are discussed.