Manipulation of skyrmions with tailored acoustic potentials

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Magnetic skyrmions are nanoscale, particle-like swirling spin textures with a non-zero topological charge that appear in some condensed matter systems such as magnetic multilayers. About a decade ago it was predicted that they could be transported along a magnetic wire using small amounts of electrical current, and this has led to a variety of proposals for their use in magnetic memory and non-von Neumann computing architectures. However, in practice skyrmion motion is hindered by grain boundaries and other imperfections in the magnetic material, meaning that far more current is needed than predicted, leading to energy wastage mainly in the form of Joule heating. Rather than try to refine the magnetic material any further, what we will do in this project is avoid using currents altogether, and instead use surface acoustic waves (SAWs) to manipulate skyrmions. The aim of the PhD project is to further investigate the manipulation of skyrmions by SAWs, mainly by experiment, but complemented by micromagnetic simulations. Synthetic antiferromagnetic (SAF) multilayers that we currently study contain skyrmions that are even smaller than those in ferromagnets, and hold promise for low-power manipulation, and it is SAF materials that will mainly be investigated in this project. The main challenges of the project are to fabricate GHz frequency SAW transducers for the manipulation of these nanoscale skyrmions and to detect the skyrmion response. The Royce Deposition System and magnetic characterisation tools within the Condensed Matter Group will be used to deposit and study the SAF multilayers. SAW transducers will be fabricated in the university's Wolfson cleanroom. Structural characterisation and microscopy will be performed using Bragg Centre facilities. Synchrotron techniques will complement the magnetic imaging available in Leeds.