pre-print of our paper at <https://link.aps.org/doi/10.1103/PhysRevB.96.184301>, © 2017 American Physical Society.
author:
- 'T. Weber'
- 'B. Roessli'
- 'C. Stock'
- 'T. Keller'
- 'K. Schmalzl'
- 'F. Bourdarot'
- 'R. Georgii'
- 'R. A. Ewings'
- 'R. S. Perry'
- 'P. Böni'
bibliography:
- 'mvo.bib'
title: 'Transverse acoustic phonon anomalies at intermediate wavevectors in MgV$_{2}$O$_{4}$'
---

 \[sec:intro\] Introduction 
============================

Magnetically frustrated and orbitally degenerate materials are of high interest to study the coupling between the lattice, spin, and orbital degrees of freedom. [@Tokura03; @Millis98; @Rudolf07] One important class are the spinels, i.e. minerals possessing the chemical formula [$\textrm{A}^{2+}\textrm{B}^{3+}_2\textrm{X}^{2-}_4$]{} where A and B are divalent and trivalent metallic cations, respectively, and in most cases X are oxygen ions. The anions form a face-centred cubic lattice with 32 ions in the unit cell. The interstices of the close-packed structure consist of 8 tetrahedral and 16 octahedral sites which – in a normal spinel – are occupied by the smaller A and B cations, respectively (Fig. \[fig:spinel\]). The ions occupying the tetrahedral sites constitute a diamond lattice and the ions in the octahedral sites form a corner-sharing pyrochlore lattice, which is an archetype for geometrically frustrated magnetic systems. [@Anderson56]

![\[fig:spinel\] Conventional 