Ab initio calculation of the magnetic Gibbs free energy using magnetically constrained supercells: electronic and magnetoelastic mechanisms of first-order transitions
First-order (discontinuous) phase transitions between magnetic states can provide huge entropy and temperature changes driven by the application of small external stimuli, the so-called caloric effect exploited in the design of cooling cycles [1]. We present an approach based on density functional theory (DFT) calculations of magnetically constrained supercells to compute the magnetic Gibbs free energy of materials [2,3]. The minimization of this free energy predicts and explains the character of phase transitions at finite temperature in terms of both purely electronic and magnetoelastic mechanisms, the former arising from the presence of multisite magnetic interactions [4]. The performance of two different DFT codes, the Vienna Ab Initio Simulation package (VASP) and the linear-scaling KKR-nano suitable for thousands of atoms (jukkr.fz-juelich.de), will be demonstrated. Results obtained for some materials, including the triangular antiferromagnetic state in antiperovskite systems, will be shown and compared with experiment.
[1] X. Moya et al., Nature Materials 13, 439 (2014).
[2] B.L. Gyorffy et al., J. Phys. F: 15, 1337 (1985).
[3] E. Mendive-Tapia, J. Neugebauer, and T. Hickel, Phys. Rev. B 105, 064425 (2022).
[4] E. Mendive-Tapia and J.B. Staunton, Phys. Rev. B 99, 144424 (2019).
Date: 17 June 2022, 14:00 (Friday, 8th week, Trinity 2022)
Venue: Zoom link: https://us02web.zoom.us/j/83583257466?pwd=Ky9aZW0xZnQ0b0FFUUkzQkd2M1VQdz09
Speaker: Dr Eduardo Mendive Tapia (Max-Planck-Institut fur Eisenforshcung, Dusseldorf)
Organising department: Department of Materials
Organiser: Joseph Prentice (University of Oxford)
Organiser contact email address: joseph.prentice@materials.ox.ac.uk
Part of: Oxford Advanced Materials Network
Booking required?: Not required
Audience: Members of the University only
Editor: Samantha Pearce