A groundbreaking study led by Thorsten Hesjedal, Gerrit van der Laan, and Shilei Zhang from Oxford, Diamond, and ShanghaiTech University has uncovered unexpected slow relaxation processes in chiral magnets, a discovery that challenges the conventional understanding of magnetic dynamics. The study highlights the critical role of topological defects in slowing down the relaxation of non-collinear magnetic states considered for emerging skyrmionics applications.
Exploring non-collinear magnetic orders
Non-collinear magnetic orders, such as spin spirals and skyrmions, have become a central topic in modern magnetism research. These complex magnetic configurations, characterised by twisted spin textures, have topological properties that make them ideal candidates for next-generation spintronic devices. In particular, magnetic skyrmions are small, stable, and can be moved about at minimal energy cost, making them ideal for advanced information storage technologies.
Typically, when these magnetic textures are disturbed, their relaxation back to equilibrium is believed to occur over a timescale of nanoseconds, as predicted by micromagnetic theories. However, the research team has discovered that under certain conditions, the relaxation processes can extend to hundreds of milliseconds or even seconds.
Revealing the slow dynamics
In their experiment, the researchers studied the archetypal chiral magnet Cu2OSeO3 using a novel time-resolved resonant elastic X-ray scattering (REXS) technique (Fig a). By applying a pulsed magnetic field and measuring the magnetic order’s response, they were able to capture the entire relaxation process in real-time. Surprisingly, the team found that both the conical and skyrmion lattice phases took up to 0.2 seconds to decay to their equilibrium state – a timescale that is eight orders of magnitude longer than conventional predictions (Fig b).
This extended relaxation is attributed to the formation of topological defects, such as dislocations and monopoles, located within the magnetic structure. These defects act as localised disturbances, slowing down the relaxation process as the system strives to unwind and return to its lowest energy state. This behaviour contrasts sharply with the rapid dynamics typically expected in magnetic systems and opens up new questions about the underlying physics of topological textures.
Read more on Diamond website
Image: 3D simulation of the skyrmion lattice. (a) Isosurface visualization (𝑚𝑧=0) of a well-ordered 3D SkX phase. During the relaxation process, topological defects (red dots) emerge that break the local skyrmion strings, as shown in (b) and (c). (d) Shared 2D skyrmion plane, cut from the transparent slices in (a)–(c). The three 𝐐𝑖 wave vectors are shown.