Dissipation phenomena and magnetic phase diagram of Cu${}_2$OSeO${}_3$ below 50 K

Abstract

The magnetic phase diagram of the chiral magnet Cu${}_2$OSeO${}_3$ has been investigated by dc magnetisation and ac susceptibility over a very large frequency range from 0.1 Hz up to 1 kHz and temperatures below 50 K. Qualitatively different phase diagrams have been obtained by applying the magnetic field along the easy $⟨100⟩$ or the hard $⟨110⟩$ crystallographic directions. Strong $\chi "$ appears close to $B_{c2}$, but only below 30 K and is more pronounced when $B$ is applied along $⟨100⟩$. In addition, the transition from the helical to the conical phase leads to two adjacent $B_{c1}$ lines below 50 K. The frequency dependence of $\chi "$ indicates the existence of very broad distributions of relaxation times both at $B_{c1}$ and $B_{c2}$. The associated very long characteristic times eventually prevent the system from reaching thermal equilibrium at low temperatures and lead to thermal hysteresis.

8 pages, 7 figures