Browsing by Author "Coïsson, Marco"

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    Magnetic properties of Fe56Pd44−xGdx thin films
    (American Institute of Physics, 2024) Sahari, Mohamed Abdennour; Olivetti, Elena Sonia; Magni, Alessandro; Fiore, Gianluca; Boudissa, Mokhtar; Tiberto, Paola; Bahamida, Saida; Coïsson, Marco
    In this paper, we have studied the effect on the structure and magnetic properties of partial Pd substitution by Gd in Fe-Pd thin films of nominal composition Fe56Pd44−xGdx (x = 1, 3, 5, and 7), deposited onto Si(100) and Si(100)/SiO2 substrates by thermal evaporation. Several techniques contribute to the characterization of their microstructure and magnetic properties, such as x-ray diffraction (XRD), scanning electron microscopy, alternating gradient field magnetometry, and magnetic force microscopy (MFM). X-ray diffraction shows that the as-deposited films are either amorphous or contain a disordered FePd phase, depending on the film thickness. The transformation of disordered fcc-FePd into ordered fct-FePd has been induced by a heat treatment at 530 °C for 4 h. The addition of gadolinium leads to a reduction in the coercivity as a consequence of the emergence of soft phases and of the progressive reduction of the fct-FePd phase, which is primarily responsible for the observed maze magnetic domains. The exchange coupling between the soft phase and the hard fct-FePd phase is demonstrated by first-order reversal curves (FORCs).
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    Phase transformations and magnetostriction in Fe100- x Gax bulk alloys
    (American Institute of Physics, 2022) Coïsson, Marco; Dakmak N'Dri, Kouassi; Diallo, Lindor; Olivetti, Elena S.; Martino, Luca; Sasso, Carlo P.; Celegato, Federica; Barrera, Gabriele; Bahamida, Saïda
    Fe-Ga alloys, containing 18, 21, and 23 at.% of Ga, were prepared in bulk form. In their as-cast state, they display a small magnetostriction, that is strongly improved after annealing at 1000 °C for 24 h, and subsequent rapid cooling. Multiple characterization techniques, such as x-ray diffraction, differential scanning calorimetry, Mössbauer spectroscopy, temperature-dependent magnetization curves, hysteresis loops, magnetic force microscopy, and magnetostriction measurements, were exploited in synergy to gain a deep understanding of the structure-property relationships in the studied alloys, before and after annealing. The A2 phase, which is favored in the lower range of compositions and is promoted at the expense of the D 0 3 one by annealing, is responsible for characteristic dendritic and maze magnetic domains, and for the strong improvement of the magnetostriction, which almost reaches 240 ppm (transverse configuration) in the alloys with 18 at.% of Ga, after annealing