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Magnetic properties of annealed core-shell CoPt nanoparticles
Jean-Yves Bigot1, Hasan Kesserwan, Valérie Halté
1Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, Université de Strasbourg, UMR 7504, France. bigot@ipcms.unistra.fr
Nano Letters
|February 15, 2012
Summary
Annealing crystalline cobalt-platinum (Co-Pt) core-shell nanoparticles precisely controls their magnetic properties. Higher temperatures induce a ferromagnetic phase, enhancing magnetic anisotropy and enabling precessional motion.
Area of Science:
- Applied Nanosciences
- Materials Science
- Condensed Matter Physics
Background:
- Precise control over magnetization dynamics in nanostructures is crucial for advanced applications.
- Understanding the relationship between crystalline structure and magnetic behavior is key for nanomaterial design.
Purpose of the Study:
- To control and understand the magnetization dynamics of crystalline (Co/core)-(Pt/shell) nanoparticles through annealing.
- To correlate the changes in crystalline structure induced by annealing with alterations in magnetic properties.
Main Methods:
- Electron tomography for structural analysis.
- Temperature-dependent electron microscopy to observe structural evolution.
- Time-resolved magneto-optics to probe magnetization dynamics.
Main Results:
- Mild laser annealing (370 K) preserves the core-shell structure, resulting in superparamagnetic nanoparticles with a blocking temperature (T(B)) of 66 K.
- Higher temperature annealing (up to 700 K) transforms nanoparticles into a crystalline CoPt ferromagnetic phase with a significantly increased T(B,anneal) of 347 K.
- Annealed nanoparticles exhibit increased magneto-crystalline anisotropy and characteristic precessional magnetization dynamics, absent in the superparamagnetic state.
Conclusions:
- Annealing provides a method to tune the magnetic properties of Co-Pt core-shell nanoparticles by altering their crystalline structure.
- The study establishes a direct link between structural phase transitions and the emergence of ferromagnetic behavior and complex magnetization dynamics.
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