Abstract
Topological magnetic textures are of great interest in various scientific and technological fields. To allow for precise control of nanoscale magnetism, it is of great importance to understand the role of intrinsic defects in the host material. Here we use conventional and time-resolved Lorentz microscopy to study the effect of grain size in polycrystalline permalloy films on the pinning and gyration orbits of vortex cores inside magnetic nanoislands. To assess static pinning, we use in-plane magnetic fields to shift the core across the island while recording its position. This enables us to produce highly accurate two-dimensional maps of pinning sites. Based on this technique, we can generate a quantitative map of the pinning potential for the core, which we identify as being governed by grain boundaries. Furthermore, we investigate the effects of pinning on the dynamic behavior of the vortex core using stroboscopic Lorentz microscopy, harnessing a new photoemission source that accelerates image acquisition by about two orders of magnitude. We find characteristic changes to the vortex gyration in the form of increased dissipation and enhanced bistability in samples with larger grains.
Highlights
Microscopic magnetic objects such as vortices [1–3] and skyrmions [4–6] have attracted a sustained interest in the past decade
Sample system The sample system we investigate is a magnetic vortex confined in a square permalloy (Ni80Fe20) nanoisland [1,2]
This change in grain size is less significant in the vicinity of the gold contacts as these locally increase the thermal coupling, resulting in (e) an inhomogeneous temperature profile during the annealing process
Summary
Microscopic magnetic objects such as vortices [1–3] and skyrmions [4–6] have attracted a sustained interest in the past decade. Due to their stability and unique topological properties, these textures have sparked ideas for a vast number of technological applications such as (racetrack) memories [7–10], logical-gates [11,12], and neuromorphic computing [13]. Higher real-space resolution is offered by spin-polarized scanning tunneling microscopy in scenarios with atomic-scale defects on flat surfaces [23,32]. This method revealed a Sombrero-shaped pinning potential between vortex cores and surface adsorbates [23].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
