Investigation and Manipulation of Single Magnetic Skyrmions

Dr Niklas Romming
University of Hamburg, Germany
4pm Tuesday 26 May 2015
Conference Room, 2nd Floor Newton Building, UNSW

Magnetism in thin films can significantly deviate from commonly known magnetic configurations in bulk systems due to low dimensionality, hybridization effects, a change of the lattice constant, stacking and broken inversion symmetry at interfaces. This can lead to non-collinear spin states such as spin spirals or skyrmions. Especially skyrmions offer great potential as information carriers in future robust, high-density, and energy-efficient spintronic devices. A focus of current research is the preparation, detection, and manipulation of individual skyrmions for an implementation in devices.

Here we investigate the atomic-scale spin structure of individual isolated skyrmions in an ultrathin film in real space by spin-polarized scanning tunneling microscopy. Their axial symmetry as well as their unique rotational sense is revealed by using both out-of-plane and in-plane sensitive tips. The size and shape of skyrmions change as a function of magnetic field. Via an analytical expression for the description of skyrmions, the experimental data can be connected to the original theoretical model describing chiral skyrmions1.
We then report the discovery of a novel detection mechanism exploiting the resistance change due to the non-collinearity of a spin texture: mixing between the spin channels locally alters the electronic structure in a skyrmion with respect to the ferromagnetic background leading to a drastic change in tunnel conductance. This non-collinear magnetoresistance (NCMR) promises to be a reliable all-electrical detection scheme for skyrmions with an easy implementation into device architectures2.

We then demonstrate how individual skyrmions can be written and deleted in a controlled fashion with locally injected spin-polarized currents from a scanning tunneling microscope. An external magnetic field is used to tune the energy landscape, and the temperature is adjusted to prevent thermally activated switching between topologically distinct states. Switching rate and direction can then be controlled by the parameters used for current injection3.

[1] Romming, N., Kubetzka, A., Hanneken, Ch., von Bergmann, K. & Wiesendanger, R. Field-Dependent Size and Shape of Single Magnetic Skyrmions. PRL 114, 177203 (2015).
[2] Hanneken, Ch., Otte, F., Kubetzka, A., Dupé, B., Romming, N., von Bergmann, K., Wiesendanger, R. & Heinze, S. Electrical detection of magnetic skyrmions by non-collinear magnetoresistance. submitted (2015).
[3] Romming, N., Hanneken, Ch., Menzel, M., Bickel, J. E., Wolter, B., von Bergmann, K., Kubetzka, A. & Wiesendanger, R. Writing and Deleting Single Magnetic Skyrmions. Science 341, 636 (2013).