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Magnetism of anisotropic nano-objects: Magnetic and neutron studies of Co(1-x)Ni(x) nanowires.

Abstract : Magnetism of individual nano-objects is a very active research field thanks to the development of original synthesis routes and investigation tools. This thesis aims at probing the magnetism of nanowires synthesized via a pure chemical route, the polyol process. This process provides a large variety and an excellent crystallinity of the synthesized nanowires. This process allows to tune the diameter of the nanowires from 7nm to 20nm leading to coherent magnetization reversal in the nanowires. I show how the large shape and magnetocrystalline anisotropies provide large coercivities compared to magnetic nanowires synthesized via other routes. Furthermore, the oxidation of such objects has also been investigated. Magnetic measurements has revealed unsual temperature dependencies of both the coercive and exchange fields, emphasizing the role of the superparamagnetic fluctuations of the CoO antiferromagnetic grains in the Exchange Bias effect. Finally, this thesis also aims at developing Polarized Small Angle Neutron Scattering to probe magnetism in complex nano-objects. Such a technique has been ignored until now to study magnetic anisotropic nano-objects despite being well adapted. The key ingredient to carry through such a study is the perfect alignment of the nanowires. This is why, besides the nanowires synthesized via the polyol process, Polarized Small Angle neutron Scattering measurements have been performed on arrays of magnetic nanowires included in porous alumina membranes.
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Submitted on : Wednesday, April 7, 2010 - 3:27:54 PM
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Thomas Maurer. Magnetism of anisotropic nano-objects: Magnetic and neutron studies of Co(1-x)Ni(x) nanowires.. Physics [physics]. Université Paris Sud - Paris XI, 2009. English. ⟨tel-00471180⟩

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