Imaging magnetic spiral phases, skyrmion clusters, and skyrmion displacements at the surface of bulk Cu$_2$OSeO$_3$

TL;DR

This study uses high-resolution magnetic microscopy to image and analyze surface magnetic phases, skyrmion clusters, and their controllability in bulk Cu₂OSeO₃, revealing surface-specific phenomena and local skyrmion manipulation.

Contribution

It provides the first real-space imaging of surface magnetic textures and skyrmion behavior in Cu₂OSeO₃, demonstrating surface-specific phases and local skyrmion control.

Findings

Surface hosts a distinct in-plane stripe phase.

Skyrmion clusters emerge from ruptured spiral domains.

Local skyrmion displacement is achievable via electric potential.

Abstract

Surfaces -- by breaking bulk symmetries, introducing roughness, or hosting defects -- can significantly influence magnetic order in magnetic materials. Determining their effect on the complex nanometer-scale phases present in certain non-centrosymmetric magnets is an outstanding problem requiring high-resolution magnetic microscopy. Here, we use scanning SQUID-on-tip microscopy to image the surface of bulk Cu$_2$OSeO$_3$ at low temperature and in a magnetic field applied along $\left\langle100\right\rangle$. Real-space maps measured as a function of applied field reveal the microscopic structure of the magnetic phases and their transitions. In low applied field, we observe a magnetic texture consistent with an in-plane stripe phase, pointing to the existence of a distinct surface state. In the low-temperature skyrmion phase, the surface is populated by clusters of disordered skyrmions, which emerge from rupturing domains of the tilted spiral phase. Furthermore, we displace individual skyrmions from their pinning sites by applying an electric potential to the scanning probe, thereby demonstrating local skyrmion control at the surface of a magnetoelectric insulator.