In this project we will study magnetic skyrmions, nanoscale swirls of spins that possess a special topology. They appear in properly designed magnetic multilayers at room temperature and are candidates for next-generation data storage technology.
It is now over a decade since the carbon footprint of the internet grew larger than that of commercial air travel, much of this energy is used to physically spin hard disks, write data to them, and write and refresh volatile memory. To drive skyrmions along a crystal using spin torque requires several orders of magnitude less current density then driving magnetic domains under ideal conditions, but this is not seen in practice in these systems so far. Magnetic skyrmions thus offer the prospect of vastly reducing the energy needed to write and store digital data if their properties can be controlled.
Two current challenges are that skyrmions do not move in the direction they are pushed by an electrical current, but actually move at an angle, due to the so-called skyrmion Hall effect arising from their topological charge, and are also expected to have reduced mobility as the size is reduced, affecting the reliability and speed of device operation.
To address these issues, here we will stabilise skyrmions in synthetic antiferromagnetic multilayers and study their current-driven dynamics, based two recent breakthroughs in the Leeds condensed matter physics group: our being able to stabilise skyrmions as a topological structure in a magnetic multilayer (Zeissler et al., Nature Nanotech., 2018), and being able to move coupled topological defects—domain walls—at low current density in a pair of antiferromagnetically coupled layers (Lepadatu et al., Sci. Reports, 2017). Cancelling out the topological charge by using a synthetic antiferromagnet is expected to overcome both the skyrmion Hall angle and reduced mobility problems.
The project is partially sponsored by the National Physical Laboratory (NPL), in Teddington near London, through the CASE scheme. We expect close collaboration with NPL in the project, including secondments at NPL by the successful candidate.