Self-diffusion of Fe and Pt in L10-Ordered FePt: Molecular Dynamics simulation

S.I Konorev,R Kozubski,M Albrecht,I.A Vladymyrskyi

doi:10.1016/j.commatsci.2021.110337

Abstract

Vacancy-mediated lattice diffusion coefficients of Fe and Pt atoms in the chemically ordered L10-FePt phase at temperatures between 1300 and 1600 K were evaluated by means of Molecular Dynamics (MD) simulations. Due to the anisotropic structure of the L10-ordered FePt phase, Fe and Pt diffusion fluxes and the resulting self-diffusion coefficients were considered along and perpendicular to the [001] crystallographic direction. In view of a very low vacancy concentration in real FePt single crystals, steady state conditions of the simulated process were approximated by specifically scaling the self-diffusion coefficients estimated for higher vacancy concentrations to the equilibrium vacancy concentration. This procedure involved the calculation of vacancy formation energies which appeared temperature dependent. The validity of this approach was thoroughly tested and the final results were analyzed and compared to the relevant literature data. The evaluated temperature dependent Fe and Pt self-diffusion coefficients showed Arrhenius behavior, however, their values were much lower than the reported experimental ones. Apart from the inevitable effect of the applied quasi-empirical potentials, the discrepancies might originate from the fact that while the MD simulations addressed a single crystal of FePt defected exclusively with vacancies and antisites, the existence of fast diffusion paths along linear and planar defects cannot be excluded in real materials.

Highlights

Diffusion plays an important role in a large variety of processes in materials science [1]
Vacancy-mediated lattice diffusion coefficients of Fe and Pt atoms in the chemically ordered L10-FePt phase at temperatures between 1300 and 1600 K were evaluated by means of Molecular Dynamics (MD) simulations
Apart from the inevitable effect of the applied quasi-empirical po tentials, the discrepancies might originate from the fact that while the MD simulations addressed a single crystal of FePt defected exclusively with vacancies and antisites, the existence of fast diffusion paths along linear and planar defects cannot be excluded in real materials

Summary

Introduction

Diffusion plays an important role in a large variety of processes in materials science [1]. The activation energy of Fe diffusion calculated in their study in [0 0 1] di rection (1.65 eV) resulted in more than two times lower values than previously measured in the high temperature regime (3.8 eV, [10]). The authors attributed this difference to different diffusion mechanisms dominating in both temperature intervals: highly correlated six-jumps cycles at lower temperatures and the antistructural bridge mechanism at higher temperatures. The diffusion perpendicular to the [0 0 1] L10 direction ran by up to two orders of magnitude faster than along this direction

Results

Discussion

Conclusion