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

TL;DR

This study explores the magnetic phase diagram of Cu$_2$OSeO$_3$ below 50 K, revealing dissipation phenomena, anisotropic phase behavior, and broad relaxation time distributions affecting thermal equilibrium.

Contribution

It provides new insights into the dissipation phenomena and relaxation dynamics in Cu$_2$OSeO$_3$ across different crystallographic directions and magnetic phases.

Findings

Strong dissipation near $B_{c2}$ below 30 K

Different phase diagrams for different crystallographic directions

Broad relaxation time distributions causing thermal hysteresis

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 $\langle100\rangle$ or the hard $\langle110\rangle$ crystallographic directions. Strong $\chi"$ appears close to $B_{c2}$, but only below 30 K and is more pronounced when $B$ is applied along $\langle100\rangle$. 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.