Monte Carlo simulation of equilibrium L10 ordering in FePt nanoparticles
| Autor: | Roman V. Chepulskii, W.H. Butler, J. Velev |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
010302 applied physics
Condensed Matter - Materials Science Range (particle radiation) Phase transition Materials science Annealing (metallurgy) Monte Carlo method General Physics and Astronomy Nanoparticle Thermodynamics 02 engineering and technology 021001 nanoscience & nanotechnology 01 natural sciences Inflection point 0103 physical sciences Particle size 0210 nano-technology Condensed Matter - Statistical Mechanics Mixing (physics) |
| Zdroj: | Journal of Applied Physics. 97:10J311 |
| ISSN: | 1089-7550 0021-8979 |
| Popis: | First, second and third nearest neighbor mixing potentials for FePt alloys, were calculated from first principles using a Connolly-Williams approach. Using the mixing potentials obtained in this manner, the dependency of equilibrium L1_0 ordering on temperature was studied for bulk and for a spherical nanoparticle with 3.5nm diameter at equiatomic composition by use of Monte Carlo simulation and the analytical ring approximation. The calculated order-disorder temperature for bulk (1495-1514 K) was in relatively good agreement (4% error) with the experimental value (1572K). For nanoparticles of finite size, the (long range) order parameter changed continuously from unity to zero with increasing temperature. Rather than a discontinuity indicative of a phase transition we obtained an inflection point in the order as a function of temperature. This inflection point occurred at a temperature below the bulk phase transition temperature and which decreased as the particle size decreased. Our calculations predict that 3.5nm diameter particles in configurational equilibrium at 600 C (a typical annealing temperature for promoting L1_0 ordering) have an L1_0 order parameter of 0.83 (compared to a maximum possible value equal to unity). According to our investigations, the experimental absence of (relatively) high L1_0 order in 3.5nm diameter nanoparticles annealed at 600 C or below is primarily a problem of kinetics rather than equilibrium |
| Databáze: | OpenAIRE |
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