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Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films

Wolloch, M. and Gruner, M. E. and Keune, W. and Mohn, P. and Redinger, J. and Hofer, F. and Suess, D. and Podloucky, R. and Landers, J. and Salamon, S. and Scheibel, F. and Spoddig, D. and Witte, R. and Roldan Cuenya, B. and Gutfleisch, O. and Hu, M. Y. and Zhao, J. and Toellner, T. and Alp, E. E. and Siewert, M. and Entel, P. and Pentcheva, R. and Wende, H. (2016):
Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films.
94, In: Physical Review B, (17), American Physical Society, p. 174435, ISSN 2469-9950, [Online-Edition: http://dx.doi.org/10.1103/PhysRevB.94.174435],
[Article]

Abstract

We present phonon dispersions, element-resolved vibrational density of states (VDOS) and corresponding thermodynamic properties obtained by a combination of density functional theory (DFT) and nuclear resonant inelastic x-ray scattering (NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and thin epitaxial films. We see distinct differences in the VDOS of the antiferromagnetic (AF) and ferromagnetic (FM) phases, which provide a microscopic proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a particular sensitivity to the slight tetragonal distortions present in epitaxial films, which is not encountered in the AF phase. This results in a notable change in lattice entropy, which is important for the comparison between thin film and bulk results. Our calculations confirm the recently reported lattice instability in the AF phase. The imaginary frequencies at the X point depend critically on the Fe magnetic moment and atomic volume. Analyzing these nonvibrational modes leads to the discovery of a stable monoclinic ground-state structure, which is robustly predicted from DFT but not verified in our thin film experiments. Specific heat, entropy, and free energy calculated within the quasiharmonic approximation suggest that the new phase is possibly suppressed because of its relatively smaller lattice entropy. In the bulk phase, lattice vibrations contribute with the same sign and in similar magnitude to the isostructural AF-FM phase transition as excitations of the electronic and magnetic subsystems demonstrating that lattice degrees of freedom need to be included in thermodynamic modeling.

Item Type: Article
Erschienen: 2016
Creators: Wolloch, M. and Gruner, M. E. and Keune, W. and Mohn, P. and Redinger, J. and Hofer, F. and Suess, D. and Podloucky, R. and Landers, J. and Salamon, S. and Scheibel, F. and Spoddig, D. and Witte, R. and Roldan Cuenya, B. and Gutfleisch, O. and Hu, M. Y. and Zhao, J. and Toellner, T. and Alp, E. E. and Siewert, M. and Entel, P. and Pentcheva, R. and Wende, H.
Title: Impact of lattice dynamics on the phase stability of metamagnetic FeRh: Bulk and thin films
Language: English
Abstract:

We present phonon dispersions, element-resolved vibrational density of states (VDOS) and corresponding thermodynamic properties obtained by a combination of density functional theory (DFT) and nuclear resonant inelastic x-ray scattering (NRIXS) across the metamagnetic transition of B2 FeRh in the bulk material and thin epitaxial films. We see distinct differences in the VDOS of the antiferromagnetic (AF) and ferromagnetic (FM) phases, which provide a microscopic proof of strong spin-phonon coupling in FeRh. The FM VDOS exhibits a particular sensitivity to the slight tetragonal distortions present in epitaxial films, which is not encountered in the AF phase. This results in a notable change in lattice entropy, which is important for the comparison between thin film and bulk results. Our calculations confirm the recently reported lattice instability in the AF phase. The imaginary frequencies at the X point depend critically on the Fe magnetic moment and atomic volume. Analyzing these nonvibrational modes leads to the discovery of a stable monoclinic ground-state structure, which is robustly predicted from DFT but not verified in our thin film experiments. Specific heat, entropy, and free energy calculated within the quasiharmonic approximation suggest that the new phase is possibly suppressed because of its relatively smaller lattice entropy. In the bulk phase, lattice vibrations contribute with the same sign and in similar magnitude to the isostructural AF-FM phase transition as excitations of the electronic and magnetic subsystems demonstrating that lattice degrees of freedom need to be included in thermodynamic modeling.

Journal or Publication Title: Physical Review B
Volume: 94
Number: 17
Publisher: American Physical Society
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 09 Jan 2017 13:33
Official URL: http://dx.doi.org/10.1103/PhysRevB.94.174435
Identification Number: doi:10.1103/PhysRevB.94.174435
Funders: M. Wolloch, P. Mohn, J. Redinger, and D. Suess acknowledge the support by the Austrian Science Fund (FWF) [SFB ViCoM F4109-N28 and F4112-N28]., P. Entel M. E. Gruner, O. Gutfleisch, F. Scheibel, D. Spoddig, and H. Wende acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG) within the priority program SPP 1599 (GR3498/3-2, GU514/6-2, WE2623/12-2, AC63/4-2)., Beatriz Roldan acknowledges the support of the US National Science Foundation (NSF-DMR 1207065)., This work was supported by the DFG SPP 1681 (WE2623/7-1), FOR 1509 (WE2623/13-2), and by Stiftung Mercator (MERCUR)., The authors also appreciate the ample support of computer resources by the Vienna Scientific Cluster (VSC) and the use of the Cray XT6/m and MagnitUDE (DFG grant INST 20876/209-1 FUGG) supercomputers of the CCSS University of Duisburg-Essen., This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
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