Formation and rotation of skyrmion crystal in the chiral-lattice insulator Cu2OSeO3

TL;DR

This study uses neutron scattering to investigate skyrmion formation and rotation in Cu2OSeO3, revealing temperature-dependent changes in skyrmion lattice orientation and the influence of magnetic fields on their configuration.

Contribution

It demonstrates the temperature-dependent reorientation of skyrmion lattices and the magnetic field-induced rotation near phase boundaries in a chiral-lattice insulator.

Findings

Skyrmion lattice orientation changes from <110> to <001> near T_c.

Magnetic field induces a 30° rotation of skyrmion lattice near phase boundary.

Helical spin order identified in zero field.

Abstract

Small angle neutron scattering experiments were performed on a bulk single crystal of chiral-lattice multiferroic insulator Cu$_2$OSeO$_3$. In the absence of an external magnetic field, helical spin order with magnetic modulation vector $q \parallel <001>$ was identified. When a magnetic field is applied, a triple-$q$ magnetic structure emerges normal to the field in the A-phase just below the magnetic ordering temperature $T_c$, which suggests the formation of a triangular lattice of skyrmions. Notably, the favorable $q$-direction in the A-phase changes from $q \parallel <110>$ to $q \parallel <001>$ upon approaching $T_c$. Near the phase boundary between these two states, the external magnetic field induces a 30$^\circ$-rotation of the skyrmion lattice. This suggests a delicate balance between the magnetic anisotropy and the spin texture near $T_c$, such that even a small perturbation significantly affects the ordering pattern of the skyrmions.