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Size and shape effects on the order-disorder phase transition in CoPt nanoparticles
D Alloyeau1, C Ricolleau, C Mottet
1Laboratoire Matériaux et Phénomènes Quantiques, Université Paris 7/CNRS, Bâtiment Condorcet, 4 rue Elsa Morante, 75205 Paris Cedex 13, France. alloyeau.damien@gmail.com
Nature Materials
|November 17, 2009
Summary
Chemically ordered CoPt nanoparticles show significantly reduced phase transition temperatures compared to bulk materials. Nanoparticle size and shape critically influence this transition, impacting magnetic storage applications.
Area of Science:
- Materials Science
- Nanotechnology
- Condensed Matter Physics
Background:
- Chemically ordered bimetallic nanoparticles are crucial for advanced magnetic-storage applications.
- Understanding size-dependent physical properties of sub-10 nm nanomagnets is essential.
- Cobalt-platinum (CoPt) nanoparticles are investigated for their magnetic properties.
Purpose of the Study:
- To investigate the effects of size and morphology on the order-disorder phase transition temperature of CoPt nanoparticles (T(C)(NP)).
- To compare experimental findings with theoretical simulations for nanomagnets.
Main Methods:
- Experimental investigation using transmission electron microscopy.
- Theoretical analysis with canonical Monte Carlo simulations.
- Characterization of nanoparticle size and morphology.
Main Results:
- For 2.4-3 nm CoPt nanoparticles, T(C)(NP) was found to be 175-325 degrees C lower than bulk material transition temperature.
- Monte Carlo simulations corroborated the experimental observations.
- Nanoparticle shape significantly affects T(C)(NP); a single dimension below 3 nm can substantially lower the transition temperature.
Conclusions:
- The order-disorder phase transition temperature of CoPt nanoparticles is highly sensitive to both size and morphology.
- Three-dimensional morphology must be considered for accurate understanding and control of nanomagnet properties.
- These findings are critical for optimizing CoPt nanoparticles in magnetic-storage technologies.
