Strain coupling behavior of the skyrmion host Cu2OSeO3 from resonant ultrasound spectroscopy

The skyrmion host Cu2OSeO3 is an important model system in understanding strain coupling associated with magnetic ordering. In addition to the skyrmion phase, Cu2OSeO3 exhibits multiple magnetic phases in response to variations in temperature and magnetic field below the transition temperature of T c∼60 K. A notable feature is the absence of symmetry-breaking strain accompanying the paramagnetic-to-ferrimagnetic transition. Resonant ultrasound spectroscopy (RUS) has been used to confirm that, although magnetoelastic coupling in Cu2OSeO3 is weak, it gives rise to small but measurable changes in elastic properties at magnetic transitions. The purpose of the present study was to investigate the strain coupling behavior of Cu2OSeO3 by collecting detailed RUS data in a dense region of magnetic phases near T c. The evolution of the elastic properties with the magnetic field, as it passes through the stability field of the skyrmion phase, characterizes the glassy behavior of skyrmions in terms of strain coupling. Overlapping acoustic loss peaks in the temperature range of approximately 50–62 K suggest that the magnetic transitions in this range involve the freezing of some dynamic aspects of the magnetic structure with an activation energy of 0.1–0.15 eV.