Thermal stability and irreversibility of skyrmion-lattice phases in Cu$_2$OSeO$_3$

TL;DR

This study uses neutron scattering to explore the stability and irreversibility of skyrmion-lattice phases in Cu$_2$OSeO$_3$, revealing distinct thermal histories that stabilize different phases and their remarkable thermal stability due to large energy barriers.

Contribution

It demonstrates the thermodynamic stability and irreversibility of skyrmion-lattice phases in Cu$_2$OSeO$_3$ and links their behavior to spin glass-like irreversibility.

Findings

Different thermal histories stabilize distinct skyrmion phases.

Once formed, skyrmion phases are highly stable and resistant to destabilization.

The phases exhibit irreversibility similar to spin glasses.

Abstract

Small angle neutron scattering measurements have been performed to study the thermodynamic stability of skyrmion-lattice phases in Cu$_2$OSeO$_3$. We found that the two distinct skyrmion-lattice phases [SkX(1) and SkX(2) phases] can be stabilized through different thermal histories; by cooling from the paramagnetic phase under finite magnetic field, the SkX(2) phase is selected. On the other hand, the 30$^{\circ}$-rotated SkX(1) phase becomes dominant by heating the sample from the ordered conical phase under finite field. This difference in stabilization is surprisingly similar to the irreversibility observed in spin glasses. The zero-field cooling results in the co-existence of the two phases. It is further found that once one of the skyrmion-lattice phases is formed, it is hardly destabilized. This indicates unusual thermal stability of the two skyrmion-lattice phases originating from an unexpectedly large energy barrier between them.