Observation of magnetic vortex pairs at room temperature in a planar {\alpha}-Fe2O3/Co heterostructure

TL;DR

This study reports the discovery of magnetic vortex pairs at room temperature in a planar Fe8O3 heterostructure, revealing novel topological structures in antiferromagnetic and ferromagnetic layers that can be manipulated by magnetic fields.

Contribution

It introduces a new form of vortices in Fe8O3 films and demonstrates their imprinting onto Co layers, advancing understanding of topological magnetic structures in heterostructures.

Findings

Magnetic vortex pairs observed at room temperature.

Ferromagnetic vortices can be manipulated by in-plane magnetic fields.

Vortex/meron pairs can be controlled and annihilated at large scales.

Abstract

Vortices are among the simplest topological structures, and occur whenever a flow field `whirls' around a one-dimensional core. They are ubiquitous to many branches of physics, from fluid dynamics to superconductivity and superfluidity, and are even predicted by some unified theories of particle interactions, where they might explain some of the largest-scale structures seen in today's Universe. In the crystalline state, vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are only observed when the effects of the dipole-dipole interaction is modified by confinement at the nanoscale, or when the parameter associated with the vorticity does not couple directly with strain. Here, we present the discovery of a novel form of vortices in antiferromagnetic (AFM) hematite ($\alpha$-Fe$_2$O$_3$) epitaxial films, in which the primary whirling parameter is the staggered magnetisation. Remarkably, ferromagnetic (FM) topological objects with the same vorticity and winding number of the $\alpha$-Fe$_2$O$_3$ vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of-plane core magnetisation), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, H$_{\parallel}$, giving rise to large-scale vortex-antivortex annihilation.