Publications Internationales

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Author: search.filters.author.Fnidiki, A.Has files: No

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    Mixed exchange-coupled soft α-(Fe80Pd20) and hard L10FePd phases in Fe64Pd36 thin films studied by first order reversal curves
    (Science direct, 2017) Bahamdia, Saida; Fnidiki, A.; Coïssonb, A.; Laggounc, G.
    Fe64Pd36 thin films have been fabricated by thermal evaporation onto single-crystal Si(1 0 0) substrates. After suitable thermal treatments, we demonstrate that two different magnetic phases can coexist in the same alloy, one α-(Fe80Pd20) which is magnetically soft, and one L10 FePd which is magnetically hard, giving rise to exchange coupling between them through their interfaces, without needing to artificially nanostructure the material. The structural and magnetic properties of as-prepared and furnace annealed samples are therefore studied by means of X-ray diffractometry, conversion electron Mössbauer spectroscopy, atomic and magnetic force microscopy and high sensitivity magnetometry. As prepared samples are characterised by different phases having soft magnetic properties: α-(Fe80Pd20) and disordered (fcc) FePd phases with different compositions. Furnace annealing in vacuum at 600 °C for one hour promotes the transformation of the fcc phases into the L10 one, while α-(Fe80Pd20) remains largely unaffected. The structural transformations are accompanied by an increase of the coercive field without any significant changes of the saturation magnetisation value. In the sample annealed at 600 °C, magnetisation reversal occurs in two steps: one at lower fields, attributed to the soft phase, and one at much larger fields, attributed to the hard phase and to the fraction of the soft one coupled to it. The exchange coupling between the two phases is demonstrated and thoroughly analysed by means of first order reversal curves
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    Effect of the A1 to L10 transformation on the structure and magnetic properties of polycrystalline Fe56Pd44 alloy thin films produced by thermal evaporation technique
    (Elsevier, 2018) Bahamida, Saida; Fnidiki, A.; Coïsson, M.; Barrera, G.; Celegato, F.; Olivetti, E.S.; Tiberto, P.; Laggoun, A.; Boudissa, M.
    X-ray diffraction, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometer techniques have been used to characterize the evolution of the microstructure and of the magnetic properties of phase transformation from disordered FePd face-centred cubic (A1) phase, to an ordered phase L10 FePd of tetragonal structure. This study was carried out by isothermally annealing in vacuum at 550 °C, as a function of annealing time, a Fe56Pd44 thin film alloy deposited on silicon substrate. The structural transformations are accompanied by a decrease of the (c/a) ratio and by an increase of the coercive field as a function of annealing time. After 10 min of annealing, the (c/a) ratio is equal to 0.945, which indicates that the disordered FePd phase is completely transformed into the ordered L10 FePd phase. By increasing annealing time, the microstructure of the alloy evolves, antiphase boundaries and twin boundaries develop. In contrast to the relationship most commonly described in the literature, that the highest coercivity corresponds to a two-phase ordered/disordered mixture, in ours studies the maximum value for coercivity corresponds to the fully ordered state. Furthermore, we propose that the high coercivity in these films is due to pinning centres of magnetic domain walls by antiphase boundaries and twin boundaries