Discovering a New Dimension in Skyrmion Dynamics

Magnetic skyrmions are known for their potential as information carriers in spintronics due to their stability, low-energy transport cost and nanoscale size. As for conventional magnetic information carriers, speed is key so the study of their dynamics is an important task on their way to device applications. In certain chiral magnets, skyrmions condense into a skyrmion lattice – a two-dimensional, closely-packed hexagonal arrangement. Unlike isolated skyrmions, this condensed skyrmion lattice exhibits a unique rigidity, meaning that the packed skyrmion structure resists to be broken up into its constituent parts. Under inhomogeneous driving forces, however, the strain on the skyrmion lattice becomes large enough to break the perfect lattice up into finite-size skyrmion crystallites. The team's experimental work demonstrated that when subjected to a linear temperature gradient, these skyrmion crystallites do not merely translate; they also rotate, a motion analogous to a rolling ball or drifting sheets of ice in the ocean, combining both translational and rotational dynamics.

Utilising time- and spatially-resolved resonant elastic X-ray scattering (REXS) at beamline I10, the researchers observed this rotational behaviour in the insulating chiral magnet Cu₂OSeO₃. Their experiments provided direct evidence of the chiral lattice torque's role in driving the skyrmion crystallites' rolling motion. The skyrmion crystallites displayed a uniform rotational chirality, which could be reversed by flipping the direction of the applied magnetic field, confirming the theoretical predictions.

Figure 1: Illustration of how skyrmions move and rotate under a temperature gradient: (a) Isolated skyrmions move in straight lines, influenced by a temperature gradient. They travel towards the bottom-right, with their speed depending on the temperature. (b) When skyrmions form crystallites, they not only move but also start to rotate due to differences in speed across the lattice. This rotation can reverse direction if the magnetic field is flipped. (c) A larger cluster of skyrmions both rolls and moves forward, similar to a rolling wheel.

Implications and future directions

This discovery not only challenges the conventional understanding of skyrmion dynamics but also introduces a new degree of freedom for manipulating these quasi-particles, potentially leading to novel applications in spintronics and data storage. The ability to control both the translational and rotational motions of skyrmions opens up exciting possibilities for future research and technology development.

Professor Shilei Zhang, the lead author, expressed his excitement about the findings:

He further stated that these rotational dynamics could be a game changer in how we design future spintronic devices.

For more information on the subject matter, please contact either Professor Shilei Zhang (ShanghaiTech University): [email protected], Professor Gerrit van der Laan (Diamond Light Source): [email protected], or Professor Thorsten Hesjedal (Oxford Physics): [email protected].

To find out more about the I10 beamline, or to discuss potential applications, please contact Principal Beamline Scientist Paul Steadman: [email protected]