Dynamic simulation of structural phase transitions in magnetic iron

Pui-Wai Ma, S. L. Dudarev, and Jan S. Wróbel
Phys. Rev. B 96, 094418 – Published 18 September 2017

Abstract

The occurrence of bcc-fcc (αγ) and fcc-bcc (γδ) phase transitions in magnetic iron stems from the interplay between magnetic excitations and lattice vibrations. However, this fact has never been confirmed by a direct dynamic simulation, treating noncollinear magnetic fluctuations and dynamics of atoms, and their coupling at a finite temperature. Starting from a large set of data generated by ab initio simulations, we derive noncollinear magnetic many-body potentials for bcc and fcc iron, describing fluctuations of atomic coordinates in the vicinity of near perfect lattice positions. We then use spin-lattice dynamic simulations to evaluate the difference between the free energies of bcc and fcc phases, assessing their relative stability within a unified dynamic picture. We find two intersections between the bcc and fcc free energy curves, which correspond to the αγ bcc-fcc and γδ fcc-bcc phase transitions. The maximum bcc-fcc free energy difference over the temperature interval between the two phase transitions is 2 meV per atom, in agreement with other experimental and theoretical estimates.

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  • Received 13 June 2017
  • Revised 7 August 2017

DOI:https://doi.org/10.1103/PhysRevB.96.094418

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Pui-Wai Ma* and S. L. Dudarev

  • Culham Centre for Fusion Energy, Abingdon, Oxfordshire OX14 3DB, United Kingdom

Jan S. Wróbel

  • Division of Materials Design, Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland

  • *leo.ma@ukaea.uk

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Issue

Vol. 96, Iss. 9 — 1 September 2017

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