Recent progress in UHV preparation and characterization methods resulted in a large variety of novel materials. Among them, magnetic multilayers have become one of the mostly investigated system due to interesting phenomena like oscillating indirect exchange coupling, spin dependent electron transport, or large perpendicular anisotropies. An attractive possibility given by the molecular beam epitaxy is to grow the multilayer structures on atomic scale by the so-called atomic layer deposition. At the low thickness limit, a multilayer structure, in which few atomic layers of different metals are stacked alternately, is expected to be an artificial ordered alloy. Such artificial material, which does not exist in the equilibrium bulk phase, was constructed for the first time as the AuFe ordered alloy of the L1_{0} structure. Our conversion electron Mössbauer spectroscopy studies of this system verified the existence of the tetragonal phase, which is responsible for the perpendicular anisotropy. The ordering process is influenced by the complicated growth of Fe on Au, as shown by the atomic scale scanning tunneling microscopy investigations. Other systems to be presented are FeAl (strong ordering mechanism in the bulk) and FeCr (miscible in the wide concentration range) monoatomic
Series of Fe_3O_4/MgO(001) and Fe_3O_4/Fe/MgO(001) films (single- and bi-layer films, respectively) with a total layer thickness in the range of 20 ÷ 150 nm were investigated by the Rutherford backscattering spectrometry (2 MeV He^{+} ion beam), by the Rutherford backscattering spectrometry channeling experiments (1.5 MeV He^{+} ion beam). Depending on the layer thickness of each layer and the film geometry, a single Fe peak and/or a double-anomaly feature was revealed in the Rutherford backscattering spectra. For all films no magnesium presence in the surface layer was observed. For both single- and bi-layer films with a total layer thickness less than 60 nm only one minimum was observed in the channeling curves, while a double minimum was revealed for the bi-layer films with a larger thickness. X-ray reflectometry measurements have revealed that the film density is the same as that of the bulk one.
We investigated the magnetic properties of ultrathin magnetite films deposited directly on MgO(001) and on a Fe(001) buffer layer. In both cases the magnetite surface structure could be identified using low energy electron diffraction. The conversion electron MÖssbauer spectroscopy measurements proved that, for magnetite films deposited on the Fe buffer, superparamagnetic relaxation was strongly suppressed. The effect of a Fe overlayer on the magnetite film grown directly on MgO is considerably weaker. Longitudinal Kerr magnetometry indicated the presence of the ferromagnetic interfacial coupling between Fe and magnetite films. We conclude that the density of antiphase boundaries for films grown on the Fe buffer is lower than that of Fe_3O_4/MgO films.
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