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Morphological and magnetic study at the interfaces of (Fe/Si)3 multilayers

AutorBartolomé, Juan; Badía-Romano, L.; Rubín, Javier; Bürgler, D. E.; Ovchinnikov, S.; Varnakov, S. N.
Fecha de publicación2013
ResumenThe field of research on nanostructures of ferromagnetic metal/semiconductormaterials is subject of interest due to their unique physical properties for applications in microelectronics, spintronics, etc. In this work we focus our research on the particular case of (Fe/Si)n multilayer magnetic structures with an odd number of Fe layers and their interfaces. The interlayer exchange coupling (IEC) between two ferromagnetic layers across a nonmagnetic spacer leads to applications in mass storage, nonvolatile memory and sensors. However, the presence of nonmagneticsilicides decreases the current spin polarization in the silicon spacerlayer and affects the mechanism of IEC. It is, therefore, of utmost importanceto control the interlayer composition. Samples are prepared by sequential deposition of Fe/Sibilayers in molecular beam epitaxy (MBE) set-ups in ultrahigh vacuum and at room temperature. Two different substrates have been used: a Si(100) wafer with a thin SiO2 buffer layer (type A) and an in situ prepared buffer layer of Ag(100) on Fe/GaAs(100) (type B). To characterize the morphology and chemical constitution of the films and their interfaces, high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS), angle-resolved x-ray photoelectron spectroscopy (ARXPS), high energy x-ray photoelectron spectroscopy (HAXPES), x-ray reflectivity (XRR), and conversion electron Mössbauer spectroscopy (CEMS) have been used. The magnetic properties were obtained from SQUID magnetometry and magneto-optic (MOKE) imaging of the magnetic domain structures. From the comprehensive analysis of all data we conclude that the as-deposited A and B samples show non-magnetic Fe silicide formation at the nominal Si spacers. As temperature is increased, at about 400 K, the A samples undergo diffusion of Si into the Fe films, reacting to form even more non-magnetic silicide. In contrast, in the B samples, the chemical reaction implies the transformation of non-magnetic silicides formed during deposition into ferromagnetic Fe3Si in a first step, and into non-magnetic silicides like ε-FeSi in a second step. The difference is attributed to the substrate, which in the case A is capable of supplying through the thin SiO2 buffer all Si needed to undergo the transition to ε-FeSi, while in the case B this cannot occur since the substrate contains no Si. The interface constitution, roughness, and asymmetry in the deposition are reviewed.
DescripciónResumen del trabajo presentado al "V Euro-Asian Symposium Trends in MAGnetism: Nanomagnetism" celebrado en Vladivostok (Rusia) del 15 al 21 de septiembre de 2013.
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