Monte Carlo simulation of equilibrium L1{sub 0} ordering in FePt nanoparticles

Journal Article · Sun May 15 04:00:00 EDT 2005 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1852351· OSTI ID:20711646

Chepulskii, R V; Velev, J; Butler, W H ^[1]

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1. Center for Materials for Information Technology, University of Alabama, Box 870209, Tuscaloosa, Alabama 35487-0209 and Department of Solid State Theory, Institute for Metal Physics, National Academy of Sciences of Ukraine (NASU), Vernadsky 36, Kyiv-142, UA-03680 (Ukraine)

First, second, and third nearest-neighbor mixing potentials for FePt alloys were calculated from first principles using the Connolly-Williams approach. Using the mixing potentials obtained in this manner, the dependency of equilibrium L1{sub 0} ordering on temperature was studied for bulk and for a spherical nanoparticle with a 3.5-nm 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 (1572 K). 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 3.5-nm diameter particles in configurational equilibrium at 600 deg. C (a typical annealing temperature for promoting L1{sub 0} ordering) have an L1{sub 0} order parameter of 0.83 (compared to a maximum possible value equal to unity). According to our investigations, the experimental absence of a (relatively) high L1{sub 0} order in 3.5-nm diameter nanoparticles annealed at 600 deg. C or below is primarily a problem of kinetics rather than equilibrium.

• OSTI ID: 20711646
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 10 Vol. 97; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANNEALING
BINARY ALLOY SYSTEMS
COMPUTERIZED SIMULATION
FERROMAGNETIC MATERIALS
IRON ALLOYS
MIXING
MONTE CARLO METHOD
ORDER PARAMETERS
ORDER-DISORDER TRANSFORMATIONS
PLATINUM ALLOYS
POTENTIALS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
TRANSITION TEMPERATURE