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Strong magnetoelastic coupling at the transition from harmonic to anharmonic order in NaFe(WO4)2 with 3d5 configuration

S. Holbein, M. Ackermann, L. Chapon, P. Steffens, A. Gukasov, A. Sazonov, O. Breunig, Y. Sanders, P. Becker, L. Bohatý, T. Lorenz, and M. Braden
Phys. Rev. B 94, 104423 – Published 21 September 2016

Abstract

The crystal structure of the double tungstate NaFe(WO4)2 arises from that of the spin-driven multiferroic MnWO4 by inserting nonmagnetic Na layers. NaFe(WO4)2 exhibits a three-dimensional incommensurate spin-spiral structure at low temperature and zero magnetic field, which, however, competes with commensurate order induced by magnetic field. The incommensurate zero-field phase corresponds to the condensation of a single irreducible representation but it does not imply ferroelectric polarization because spirals with opposite chirality coexist. Sizable anharmonic modulations emerge in this incommensurate structure, which are accompanied by large magnetoelastic anomalies, while the onset of the harmonic order is invisible in the thermal-expansion coefficient. In magnetic fields applied along the monoclinic axis, we observe a first-order transition to a commensurate structure that again is accompanied by large magnetoelastic effects. The large magnetoelastic coupling, a reduction of the b lattice parameter, is thus associated only with the commensurate order. Upon releasing the field at low temperature, the magnetic order transforms to another commensurate structure that considerably differs from the incommensurate low-temperature phase emerging upon zero-field cooling. The latter phase, which exhibits a reduced ordered moment, seems to be metastable.

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  • Received 7 July 2016
  • Revised 30 August 2016

DOI:https://doi.org/10.1103/PhysRevB.94.104423

©2016 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Holbein1,2, M. Ackermann3,*, L. Chapon2, P. Steffens2, A. Gukasov4, A. Sazonov4,†, O. Breunig1, Y. Sanders1, P. Becker3, L. Bohatý3, T. Lorenz1, and M. Braden1,‡

  • 1II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany
  • 2Institut Laue-Langevin, 71 avenue des Martyrs, F-38042 Grenoble Cedex 9, France
  • 3Abteilung Kristallographie, Institut für Geologie und Mineralogie, Universität zu Köln, Greinstrasse 6, 50939 Köln, Germany
  • 4Laboratoire Léon Brillouin, CEA/CNRS, F-91191 Gif-sur-Yvette, France

  • *Present address: TRUMPF Laser GmbH.
  • Present address: Institute of Crystallography, RWTH Aachen University, and Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum, 85747 Garching, Germany.
  • braden@ph2.uni-koeln.de

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Issue

Vol. 94, Iss. 10 — 1 September 2016

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