Tag: REXS

Discovery of a novel magnetic skyrmion surface state

Discovery of a novel magnetic skyrmion surface state

Skyrmions get perpendicular – and push the door open for high density data storage

Scientists from ShanghaiTech University, Diamond Light Source, the SOLEIL synchrotron and University of Oxford report in a recent issue of Nano Letters on their discovery of a novel skyrmion surface state that exists in applied in-plane fields – much different from the usual out-of-plane geometry. In this geometry, magnetic signals from the skyrmion lattice phase settle down in inconvenient reciprocal space locations, making resonant elastic X-ray scattering (REXS) on the chiral magnet Cu2OSeO3 a challenging job to carry out. By combining the complementary capabilities of the soft X-ray diffractometers at two synchrotrons (Diamond and SOLEIL) on the very same sample, the new state was unambiguously identified.

>Read more on the Diamond Light Source website

Image: Illustration of the conventional in-plane skyrmion state (a) and the novel perpendicular skyrmion state (b) in the non-centrosymmetric skyrmion system Cu2OSeO3. Whereas a conventional planar skyrmion takes up an area of A=d2 (d is the skyrmion diameter), a perpendicular skyrmion has a much reduced lateral footprint of A = w d (with w the width of the ridge) which is advantages for skyrmion memory applications. The REXS experiments were carried out in the RASOR diffractometer at beamline I10 in Diamond, and in RESOXS at the beamline SEXTANTS in Soleil (St. Aubin, France).

A surprising twist on skyrmions

A surprising twist on skyrmions

Magnetic tomography has been used to reconstruct a tornado-like 3D magnetic skyrmion structure.

Vortex structures are common in nature, reaching from swirls in our morning coffee to spiral galaxies in the universe. Vortices are been best known from fluid dynamics. Take the example of a tornado. Air circulates around an axis, forming a swirl, and once formed, the twisted air parcels can move, deform, and interact with their environment without disintegrating. A skyrmion is the magnetic version of a tornado which is obtained by replacing the air parcels that make up the tornado by magnetic spins, and by scaling the system down to the nanometre scale. Once formed, the ensemble of twisted spins can also move, deform, and interact with their environment without breaking up ‒ the ideal property for information carriers for memory and logic devices.

What makes a tornado stable is not only coming from its twist, but also due to its three-dimensional properties, i.e., the wind current has extra twist along the column of turbulent flow. This leads to a tight bundling of the vortex sheets at different heights along the tornado column. Similarly, such a 3D structure can also occur in magnetic skyrmions, guaranteeing their topological stability. Up to now, skyrmions have been most commonly treated as two-dimensional objects, and their exciting tornado-like structure remained unexplored. In fact, the 3D characterization of magnetic structures is a rather challenging task. A team of researchers, led by the University of Oxford and Diamond Light Source, have used the energy-dependence of resonant elastic X-ray scattering (REXS) on beamline I10 at Diamond to measure the microscopic depth dependence of ‘skyrmion tornados’ in Cu2OSeO3. In their work, published in Proceedings of the National Academy of Sciences, they reveal a continuous change from Néel-type winding at the surface to Bloch-type winding in the bulk with increasing depth. This not only demonstrates the power of REXS for microscopic studies of surface-induced reconstructions of magnetic order, but also reveals the hidden energetics that makes magnetic skyrmions such a stable state – a crucial finding for skyrmion device engineering.

>Read more on the Diamond Light Source website

Figure: Illustration of a ‘Skyrmion tornado’. The skyrmion order changes from Néel-type at the surface to Bloch-type deeper in the sample. On the right hand side, the corresponding stereographic projections of these two boundary skyrmion patterns are shown.