Role of Morphology on the Large Coercive Behavior in Co 80 Ni 20 Nanowires
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Role of Morphology on the Large Coercive Behavior in Co80Ni20 Nanowires A. Gaul1, N. Ouar1, S. Mercone*1, F. Zighem1, F. Schoenstein1, B. Leridon2, S. Farhat1 and N. Jouini1 1 LSPM-UPR3 3407, CNRS, Université Paris 13, Sorbonne Paris Cité, 99 Avenue J.-B. Clément, 93430 Villetaneuse, France 2
LPEM, ESPCI-ParisTech, CNRS, UPMC, 10 rue Vauquelin, F-75231 Paris Cedex 5, France
*Corresponding author: [email protected] ABSTRACT Ferromagnetic metal CoNi-based nano-objects have been synthesized in a polyol media within different elaboration conditions in order to drive their morphology (i.e. enhancing their length-todiameter ratio ( d / L ) , and changing the diameter d ratio over edge T width ( d / L ) ). Transmission Electron Microscopy (TEM) studies revealed unexpected effects on the Co80Ni20 nano-objects arising from the magnetic field assisted synthesis. This gave us the opportunity to compare this latter to coming from the variation of Ruthenium (III) chloride hydrate nucleating agent concentration. A Co80Ni20 anisotropic particles elaboration was successfully achieved under zero magnetic field assisted synthesis, while an important percentage of isotropic nanoparticles appeared immediately under the application of a small magnetic field (i.e. H > 500 Oe). In the first case we were able to sharply drive both the aspect ratio and head morphology of nanowires (T and ( d / T ) ). The good crystallinity and structures symmetry of all our samples have been proved by X-Ray Diffraction (XRD) pattern analysis. Magnetic static properties showed a ferromagnetic standard behavior with a coercive field efficiency which was strongly dependent on shape parameters. The magnetic static behavior was studied within a standard Stoner-Wohlfart model as a function of the observed morphologies. Our observations are fully consistent with a shape anisotropy origin behavior of the enhanced coercivity measured as function of the decreasing ( d / L ) ratio. However, they revealed the presence of contributions to the global effective anisotropy coming from other complex terms then the shape one (i.e. conic head impressiveness, dipolar interactions and magnetocrystalline anisotropy). INTRODUCTION In past decades much attention has been focused on the synthesis of magnetic nanowires due to their potential application in the field of permanent magnets1, sensors2, high-density magnetic recording3 and spintronic devices like magnetic memory4 or microwave circuits5. Some of those applications are the natural exploitation of intrinsic properties of the anisotropic (1D) nanoobjects, such as their large magnetic shape anisotropy which generates a large coercive field. Two main effects have proven (mainly by micromagnetic simulations) to drastically change this intrinsic property: on the one hand the exchange bias effect6 rising from air-contact surface oxidations of the nanowires and on the other hand inhomogeneity of demagnetizing field at the nanowires edges coming from different head-morphologies6. In this work we focus on the pure mo
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