Elastic and anelastic behavior associated with magnetic ordering in the skyrmion host Cu₂OSeO₃

Magnetic ordering in Cu₂OSeO₃ occurs without any detectable changes in the lattice symmetry but involves significant coupling with strain. The strain coupling effects in Cu₂OSeO₃ have been investigated with a focus on the skyrmion lattice by examining elastic and anelastic properties. Resonant ultrasound spectroscopy has been used to measure these properties of a Cu₂OSeO₃ single crystal as a function of temperature and magnetic field. On heating, the skyrmion phase has been characterized by slightly softer elasticity compared to the helical phase. However, there were no obvious anomalies in elastic and anelastic properties associated with the boundary of the stability field of the skyrmion lattice. Evolution of elastic properties with magnetic field, passing through the stability field of the skyrmion lattice, showed a characteristic pattern of a glassy state, where an equilibrium state is never reached. These imply that coupling of the skyrmions with strain is extremely weak in Cu₂OSeO₃, leading to glassy or liquidlike behavior of skyrmions. Three Debye-like loss peaks were observed near ∼40, ∼50, and ∼60K. The relaxation mechanism for the 40 K loss peak has been found to have a single relaxation time. ... mehrOverlapping acoustic loss peaks in the temperature interval ∼50–62K suggest that the magnetic transitions with variable temperature in this temperature range involve freezing of some dynamic aspect(s) of the magnetic structure with an activation energy of ∼0.1–0.15 eV.