Imaging magnetic spiral phases, skyrmion clusters, and skyrmion displacements at the surface of bulk Cu2OSeO3

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 microscopy to image the surface of bulk Cu2OSeO3 at low temperature and in a magnetic field applied along $$\left\langle 100\right\rangle$$ . 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. Surfaces can significantly influence magnetic order by breaking bulk symmetries, introducing roughness, or hosting defects. Here, a microscopy study of the surface of bulk Cu2OSeO3 reveals magnetic textures associated with distinct surface states, such as in-plane magnetic stripes that are absent in the bulk, and demonstrates the local displacement of individual skyrmions by an applied electric field.