Magnon magnetoresistance, magnetization reversal and domain wall dynamics in FePt and NiFe nanostructures

In the first part of this thesis, we study the magnetization reversal process of FePtnanowires with high magnetocrystalline anisotropy. When reducing the wire width below themean dendrite width, the magnetization reversal favors a transition from the dendrite growth tothe propagation of a single domain wall (DW). Further decreasing of the width towards thedisorder length and/or the mean edge roughness leads to a large increase of coercivity, whichfinally results in a mix of DW propagation and nucleation in ultra-narrow wires.The second part focuses on the use of Magnon magnetoresistance (MMR), i.e., themagnon contribution to the resistivity, to study the magnetization reversal in nanostructures witheither perpendicular (FePt) or planar magnetization (NiFe). We showed that MMR can be usedin nanowires and nanomagnets, in particular to detect DW position in nanowires processed in asingle layer.Finally, the dynamic of DW depinning under field and current in both FePt and NiFesystems has been studied. We observe three different modes of DW depinning, which dependon the nature of defects, or on the geometry of the constriction. Statistical analysis of the pinningtime indeed shows that the depinning path can be described as simple path, serial paths oralternative paths. Additionally, the effect of DC current on all depinning mechanisms is found tobe equivalent to the effect of applied field which, allow measuring the spin transfer efficiency inthese systems.