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Probing the dynamics of twisted magnetic textures on the sub-nm scale - Markus Morgenstern - Mardi 3 mars 2020 à 11 h

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Markus Morgenstern - II. Institute of Physics B, RWTH Aachen University, Germany

Abstract

Twisted magnetic textures such as skyrmions or vortices are actively pursued as possible nonvolatile information carriers due to its large stability and due to its relatively low displace-ment current. In this talk, I present two studies by scanning tunneling microscopy probing the dynamics of such textures. Firstly, magnetic vortices (Fig. 1a) [1] are mapped while being manipulated by a 3D magnetic field (Fig. 1b). Hence, the interaction strength of the vortex core with individ-ual defects is deduced quantitatively. We find that single adsorbates on the surface pin a magnetic vortex ( 104 Fe atoms) by a Mexican hat potential [2]. Secondly, skyrmions are collapsed by single electrons while mapping the position dependent collapse rate. Comparison with first-principle based theory reveals the existence of a second collapse mechanism working like a zipper (Fig. 1e,f). This mode exists besides the well-established radial collapse (Fig. 1c,d). I will show that in-plane magnetic fields can tune the relevance of the two mechanisms.

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Figure (a) Overlay of topography (3D) and spin polarized signal (color) of Fe island containing a magnetic vortex. (b) Overlay of STM image showing two types of adsorbates (greyscale), five dI/dV images of the vortex core at five different in-plane fields B|| (red patches) and 44 center positions of the vortex core (blue circles) with lines indicating the corresponding B||. (c), (e) Spin direction maps during the collapse path of a magnetic skyrmion via the conventional radial (c) and the novel zipper like (e) mode. (d), (f) Corresponding topological density of the two modes. Numbers mark adjacent steps during the nudged elastic band calculation. SP is the energetic saddle point of the collapse.

[1] A. Wachowiak et al., Science 298, 577 (2002).
[2] C. Holl et al., arXiv:2001.06682.