Études des propriétés magnétiques de nanofils de cobalt monocristallins en réseaux ultra-denses

Abstract : The work carried out during this thesis aims at the magnetic and structural characterization of ultra-dense arrays of single crystalline cobalt hcp nanowires with the c axis parallel to the wires axis. These arrays are obtained by a physicochemical method called hybrid growth. The resulting nanomaterial is an array of vertical Co nanowires epitaxially grown on a platinum film, with diameters of 6 to 15 nm and coated with organic ligands. The crystallinity of the nanowires induces a strong anisotropy perpendicular to the substrate, giving rise to physical properties that could meet the specifications to constitute high density magnetic media. The manuscript is organized in four parts. First, a review of the literature describing the behavior of isolated magnetic nano-cylinders and dense arrays of nano-cylinders is presented. The magnetometry method used to characterize these arrays is called the FORC (First Order Reversal Curves) method. This measurement and analysis lead to the plot of FORC diagrams which contain the magnetic properties of nanowires and their interactions. The reading of these FORC diagrams being undirect, the chapter II is devoted to the description of the FORC method applied to assemblies of hysterons. Because of its reproducibility, the physico-chemical synthesis is a critical point of this study which is detailed in Chapter III. FORC magnetometry applied to two families of synthesized samples is described in Chapter IV. This investigation has required numerous micromagnetic simulations to support the assumptions made in the interpretation of FORC diagrams. This deep analysis reveals a first family in very good agreement with the theoretical models exposed in chapter I, and a second family for which the precise description requires the addition of a magnetizing interaction between nanowires in addition to the magnetostatic one.
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Alexandre Pierrot. Études des propriétés magnétiques de nanofils de cobalt monocristallins en réseaux ultra-denses. Micro et nanotechnologies/Microélectronique. INSA de Toulouse, 2019. Français. ⟨NNT : 2019ISAT0019⟩. ⟨tel-02443241⟩

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