Controlling magnetic skyrmion motion without an electric current

29 May 2018

Researchers from the University of Oxford have used resonant elastic X-ray scattering (REXS) at the Diamond Light Source (Didcot, UK) for the first demonstration of using a field gradient to control the motion of magnetic skyrmions. The work of Dr Shilei Zhang from the Thin Film Quantum Materials Group, carried out in collaboration with colleagues in Munich, Cologne, Ningbo, Lausanne, and Dresden, and published in Nature Communications, overcomes the limitations inherent in using electrical currents to control skyrmion motion and opens up new avenues of research in non-conductive (as well as conductive) skyrmion-carrying materials. Ultimately, their results bring us a step closer to high-density, low-power data storage devices based on racetrack memory. Read more on the Diamond Light Source website: Diamond Science Highlight.

Magnetic skyrmions are proposed as binary information carriers in racetrack-type memory device schemes. Therefore, the manipulation of skyrmion arrays in a shift-register-like fashion is one of the key technical requirements for device applications. Pioneering experiments established that skyrmions move under exceptionally tiny spin transfer torques, but the accurate control of the skyrmion travel, once put into motion, is an outstanding challenge. In their recent article in Nature Communications, the team presents a microscopic study of the manipulation of the trajectories of skyrmion lattice motion by a magnetic field gradient in a bulk sample of Cu2OSeO3. Using two permanent magnets, a field perpendicular to the sample is generated with well-defined (circular) constant field contours. They found that the skyrmion lattice domains exhibit a rotation, whereby reversing the field orientation and associated gradients reverses the rotation sense – fundamentally different from the behaviour reported in the context of large temperature gradients in Lorentz transmission electron microscopy experiments. The skyrmion lattice rotation is very weakly damped, i.e., the rotation, e.g. fuelled by a small magnon current, carries on for many days (in our experiments temperature gradients were below the detection limit).

The rotational motion is accompanied by a dynamical change of the skyrmion lattice domains, which is discussed in the context of domain fragmentation into ring-like racetracks, in some sense similar to the behaviour of flux-line lattices in superfluid Helium.

Their finding represents a new phenomenon that allows for the precise manipulation of a skyrmion lattice without the need of an electrical current directly interacting with the spin system, thus avoiding direct Joule heating of the magnetic storage material. This study could lead to a new spintronics device concept in which the common 1D skyrmion racetrack memory is taken for a spin.

Shilei Zhang et al. (2018). Manipulation of skyrmion motion by magnetic field gradients. Nature Communications 9, 2115. Link to the PDF.