Magnetic Properties of Annealed Core鈥揝hell CoPt Nanoparticles
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- 作者：Jean-Yves Bigot ; Hasan Kesserwan ; Val茅rie Halt茅 ; Ovidiu Ersen ; M. Simona Moldovan ; Tae Hee Kim ; Jung-tak Jang ; Jinwoo Cheon
- 刊名：Nano Letters
- 出版年：2012
- 出版时间：March 14, 2012
- 年：2012
- 卷：12
- 期：3
- 页码：1189-1197
- 全文大小：519K
- 年卷期：v.12,no.3(March 14, 2012)
- ISSN：1530-6992
文摘
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)鈥?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鈥揚t nanoparticles keep their core鈥搒hell structure and remain superparamagnetic with a blocking temperature TB = 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 TB,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鈥揚t core鈥搒hells.