The magnetic-field and temperature dependencies of ultrasound propagation and magnetization of single-crystalline CoCr2O4 have been studied in static and pulsed magnetic fields up to 14 T and 62 T, respectively. Distinct anomalies with significant changes in the sound velocity and attenuation are found in this spinel compound at the onset of long-range incommensurate spiral-spin order at T_s = 27 K and at the transition from the incommensurate to the commensurate state at T_l = 14 K, evidencing strong spin-lattice coupling. While the magnetization evolves gradually with field, steplike increments in the ultrasound clearly signal a transition into a new magneto-structural state between 6.2 and 16.5 K and at high magnetic fields. We argue that this is a high-symmetry phase with only the longitudinal component of the magnetization being ordered, while the transverse helical component remains disordered. This phase is metastable in an extended H-T phase space.
@article{arxiv.1302.5605,
title = {Unconventional magnetostructural transition in CoCr2O4 at high magnetic fields},
author = {V. Tsurkan and S. Zherlitsyn and S. Yasin and V. Felea and Y. Skourski and J. Deisenhofer and H. -A. Krug von Nidda and J. Wosnitza and A. Loidl},
journal= {arXiv preprint arXiv:1302.5605},
year = {2015}
}