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Magnetic properties of annealed core-shell CoPt nanoparticles
- Magnetic properties of annealed core-shell CoPt nanoparticles
- Bigot J.-Y.; Kesserwan H.; Halte V.; Ersen O.; Moldovan M.S.; Kim T.H.; Jang J.-T.; Cheon J.
- Ewha Authors
- SCOPUS Author ID
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- Nano Letters
- Nano Letters vol. 12, no. 3, pp. 1189 - 1197
- SCI; SCIE; SCOPUS
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- 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. © 2012 American Chemical Society.
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