Regensburg 2019 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 2: Ultrafast magnetization effects and magnetization dynamics

MA 2.11: Vortrag

Montag, 1. April 2019, 12:15–12:30, H37

Stroboscopic imaging using Lorentz TEM at radio frequencies — •John H. Gaida, Marcel Möller, Sascha Schäfer, and Claus Ropers — 4th Physical Institute, Georg-August-University, Göttingen, Germany

Lorentz microscopy is a widely applied technique for the nanoscale mapping of magnetization structures. Its time-resolved implementation offers fascinating prospects for a spatiotemporal imaging of ultrafast magnetism.

The Göttingen Ultrafast Transmission Electron Microscope (UTEM) is a recently developed instrument to study ultrafast structural, electronic and spin dynamics, driven by optical pump pulses or radiofrequency currents [1].

In this contribution, we present stroboscopic Lorentz microscopy with photoelectron pulses at high MHz-repetition rates. We use a permalloy (Ni₈₀Fe₂₀) nanoisland as a model system to benchmark the new instrument by mapping time-resolved current-driven vortex gyration. The trajectory of the vortex core is tracked with a high precision of better than 3 nm, which allows us to identify subtle deviations from an idealized gyrotropic motion. Systematic deformations of the elliptical orbit and a changing angular velocity indicate the influence of pinning centers on the trajectory. Our method can help in the design of nanoscale magnetic materials by time-resolved imaging of the dynamics of magnetic quasiparticles such as vortices or skyrmions with high spatial and temporal resolutions.

[1] A. Feist et al., Ultramicroscopy 176 (2016)