Magnetic vortices observed in haematite
Magnetic vortices observed in antiferromagnetic haematite were transferred into ferromagnetic cobalt.
Vortices are common in nature, but their formation can be hampered by long range forces. In work recently published in Nature Materials, an international team of researchers has used mapped X-ray magnetic linear and circular dichroism photoemission electron microscopy to observe magnetic vortices in thin films of antiferromagnetic haematite, and their transfer to an overlaying ferromagnetic sample. Their results suggest that the ferromagnetic vortices may be merons, and indicate that vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex–antivortex annihilation. Ferromagnetic merons can be thought of as topologically protected spin ‘bits’, and could potentially be used for information storage in meron racetrack memory devices, similar to the skyrmion racetrack memory devices currently being considered.
The starting point for this research was finding the right antiferromagnet, one with the right characteristics and is antiferromagnetic at room temperature. The answer turned out to be common rust, and a 30 nm layer of iron oxide (α-Fe2O3, the main constituent of `rust’) was placed on top of alumina crystals, then covered with a 1 nm layer of cobalt, a ferromagnet.
This could prove to be the foundation of oxide electronics, a way to move beyond silicon for the next generation of devices. The physics may be exotic, but it could allow us to build new devices that are simple and also backwards-compatible with current technologies,”
says Prof. Radaelli.
Future experiments will look to increase the density of magnetic vortices, and investigate these vortices in other materials.