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Transverse acoustic phonon anomalies at intermediate wave vectors in MgV2O4

Weber, T; Roessli, B; Stock, C; Keller, T; Schmalzl, K; Bourdarot, F; Georgii, R; ... Boeni, P; + view all (2017) Transverse acoustic phonon anomalies at intermediate wave vectors in MgV2O4. Physical Review B , 96 (18) , Article 184301. 10.1103/PhysRevB.96.184301. Green open access

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Abstract

Magnetic spinels (with chemical formula A X 2 O 4 , with X a 3 d transition metal ion) that also have an orbital degeneracy are Jahn-Teller active and hence possess a coupling between spin and lattice degrees of freedom. At high temperatures, MgV 2 O 4 is a cubic spinel based on V 3 + ions with a spin S = 1 and a triply degenerate orbital ground state. A structural transition occurs at T OO = 63 K to an orbitally ordered phase with a tetragonal unit cell followed by an antiferromagnetic transition of T N = 42 K on cooling. We apply neutron spectroscopy in single crystals of MgV 2 O 4 to show an anomaly for intermediate wave vectors at T OO associated with the acoustic phonon sensitive to the shear elastic modulus ( C 11 − C 12 ) / 2 . On warming, the shear mode softens for momentum transfers near close to half the Brillouin zone boundary, but recovers near the zone center. High resolution spin-echo measurements further illustrate a temporal broadening with increased temperature over this intermediate range of wave vectors, indicative of a reduction in phonon lifetime. A subtle shift in phonon frequencies over the same range of momentum transfers is observed with magnetic fields. We discuss this acoustic anomaly in context of coupling to orbital and charge fluctuations.

Type: Article
Title: Transverse acoustic phonon anomalies at intermediate wave vectors in MgV2O4
Open access status: An open access version is available from UCL Discovery
DOI: 10.1103/PhysRevB.96.184301
Publisher version: http://dx.doi.org/10.1103/PhysRevB.96.184301
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Physics, Condensed Matter, Physics, STRUCTURAL PHASE-TRANSITIONS, INELASTIC-NEUTRON-SCATTERING, RESOLUTION FUNCTION, MAGNETIC-FIELD, SPECTROMETERS, EXCITATIONS, SPINEL, MODE, SPECTROSCOPY, PEROVSKITES
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
URI: http://discovery.ucl.ac.uk/id/eprint/10039414
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