Skyrmion Dynamics

Skyrmion
Fig. 1. Spin structure of a skyrmion in a simplified
single layer of spins. When traversing the structure
the magnetization rotates by 360°.

Magnetic skyrmions1,2 are nanoscale magnetic quasi-particles whose spin structure can be mappedcontinuously onto a sphere.
They are promising candidates for future spintronic devices such as the skyrmion racetrack memory3, which has the potential to combine the advantages of rapid random access memory (RAM) and high capacity non-volatile hard drives.4 Skyrmions were first discovered in bulk magnetic materials where the Dzyaloshinskii-Moriya interaction (DMI) that can occur in non-centrosymmetric systems favors a chiral spin canting.5,6 Within the last years, DMI was also reported in different thin film multilayer stacks with high-perpendicular anisotropy, where skyrmions originate due to DMI resulting from the broken inversion symmetry at the interfaces. Additionally, these multilayers can generate significant spin orbit torques leading to efficient spin dynamics, making such thin film systems extremely promising for skyrmion manipulation.7

Recently, we have shown the possibility to move skyrmions efficiently in applications’ relevant geometries and at reasonable current densities.8 Our goal is to understand the dynamics of skyrmions under current and field excitations. For this, it is critical to investigate the real-time behavior of skyrmions with high temporal and spatial resolution. For direct imaging in this nanosecond and sub-nanosecond regime of dynamical phenomena we utilize imaging at synchrotron facilities. Specifically, we employ Scanning Transmission X-ray Microscopy (STXM) to reveal the behavior of skyrmion spin structures in wire and dot geometries during external excitations. Extensive simulations are used to shed light on the underlying mechanisms and corroborate the experimental data.

References:

  1. Rößler, U. K., Bogdanov, A. N. & Pfleiderer, C., Nature 442, 797–801 (2006).
  2. Mühlbauer, S. et al., Science 323, 915–919 (2009).
  3. Fert, A. et al., Nat. Nano. 8, 152–156 (2013).
  4. Tomasello, R. et al., Sci. Rep. 4, 6784 (Oktober 2014).
  5. Dzyaloshinsky, I., J. Phys. Chem. Solids 4, 241–255 (1958).
  6. Moriya, T., Phys. Rev. 120, 91–98 (1960).
  7. Brataas, A., Nat. Nano. 8, 485–486 (2013).
  8. Woo, S. et al., Nat. Mater. 15, 501–506 (2016).

Key publications :

[1] Woo, S. et al., Observation of room temperature magnetic skyrmions and their current-driven dynamics in ultrathin Co films. Nat. Mater. 15, 501–506 (2016).

[2] Büttner, F. et al., Dynamics and inertia of skyrmionic spin structures. Nature Phys. 11, 225–228 (2015).