title: Magnetic properties of annealed core-shell CoPt nanoparticles.
abstract: A precise control and understanding of the magnetization dynamics of nanostructures is an important topic in applied nanosciences. Herein, we perform such control by annealing crystalline (Co/core)-(Pt/shell) nanoparticles. Using electron tomography, temperature dependent electron microscopy and time-resolved magneto-optics, we establish a clear correlation between the magnetization dynamics and the crystalline structure of the nanoparticles. For a mild laser annealing (370 K) the Co-Pt nanoparticles keep their core-shell structure and remain superparamagnetic with a blocking temperature T(B) = 66 K. Their time-resolved reflectivity shows that they are locally organized into a supra-crystalline ordered layer in the region of the laser spot. In contrast, a thermal annealing at higher temperatures (up to 700 K) modifies the structure of the individual nanoparticles into a CoPt crystalline ferromagnetic phase, with T(B,anneal) = 347 K. Correspondingly, the magneto-crystalline anisotropy of the annealed CoPt nanoparticles increases and their magnetization dynamics displays a motion of precession, characteristic of ferromagnetic nanostructures and which is absent in the superparamagnetic Co-Pt core-shells.
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, Université de Strasbourg, UMR 7504, France. bigot@ipcms.unistra.fr
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Bigot
authors.forename: Hasan
authors.initials: H
authors.lastname: Kesserwan
authors.forename: Valérie
authors.initials: V
authors.lastname: Halté
authors.forename: Ovidiu
authors.initials: O
authors.lastname: Ersen
authors.forename: M Simona
authors.initials: MS
authors.lastname: Moldovan
authors.forename: Tae Hee
authors.initials: TH
authors.lastname: Kim
authors.forename: Jung-tak
authors.initials: JT
authors.lastname: Jang
authors.forename: Jinwoo
authors.initials: J
authors.lastname: Cheon
mesh_terms: D000497:Alloys / Q000737:chemistry*; D017097:Electric Impedance; D004574:Electromagnetic Fields; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D016062:Porosity
chemical_list: D000497:Alloys; C477450:cobalt platinum alloy