Zero-field magnetic skyrmions in model-type systems studied with STM*

Magnetic skyrmions can be stabilized in thin films by interface-induced Dzyaloshinskii-Moriya interactions that compete with exchange interactions. Such skyrmions can become lowest energy states in applied magnetic fields but are often only metastable configurations in zero magnetic field. Spin-polarized scanning tunneling microscopy is a powerful tool to characterize such magnetic textures down to the atomic scale [1].
We have studied the magnetic properties of a Rh/Co atomic bilayer on Ir(111) using spin-resolved scanning tunneling microscopy. Depending on the stacking of the Rh monolayer we observe a significant number of domain walls with unique rotational sense in the otherwise out-of-plane magnetized film. We also identify small circular magnetic objects in the virgin state. They coexist in both oppositely magnetized ferromagnetic domains and resemble zero-field magnetic skyrmions with up- or down-pointing core. Ab-initio calculations in combination with spin dynamics simulations shed light on the origin of these unusual properties [2]. The domain walls and skyrmions can be imaged also with non-spin-polarized probe tips due to the contribution of the non-collinear magnetoresistance (NCMR) [3,4]. It arises from spin-mixing and leads to variations in the differential conductance depending on the details of the local spin texture.

References:
[1] K. von Bergmann et al., J. Phys.: Condens. Matter 26, 394002 (2014).
[2] S. Meyer et al., Nature Commun. 10, 3823 (2019).
[3] C. Hanneken et al., Nature Nanotech. 10, 1039 (2015).
[4] M. Perini et al., Phys. Rev. Lett. 123, 237205 (2019).