Mapping ultrafast magnetic processes in transmission electron microscopy
Sascha Schäfer (4th Physical Institute ̶̶ Solids and Nanostructures, University of Göttingen)

State-of-the-art transmission electron microscopy (TEM) now routinely yields an in-depth characterization of the structure and composition of inhomogeneous systems down to atomic dimensions. In addition, advanced TEM techniques such as Lorentz microscopy and electron holography enable a quantitative spatial mapping of the electric and magnetic fields in nanoscale systems. However, the temporal resolution achieved with TEM electron detectors is typically insufficient to record the evolution of fast magnetic processes potentially relevant in future information storage devices.
In this seminar, I will present two recent approaches, which allow to address ultrafast magnetic dynamics in electron microscopy. Firstly, implementing an in-situ femtosecond optical excitation in a TEM, we demonstrate the optically induced formation of a dense network of magnetic vortices and anti-vortices in a homogeneous iron thin film. The nanoscale metastable texture forms by an ultrafast temperature quench across the ferromagnetic phase transition and exhibits glass-like properties [1].
Secondly, we developed an ultrafast transmission electron microscope (UTEM) [2,3], which utilizes femtosecond electron pulses for stroboscopic nanoscale TEM imaging. I will show one example, in which we spatially and temporally map the ultrafast optical demagnetization in permalloy nanodisc structures [4], and present our current progress towards UTEM imaging of current-driven vortex and domain-wall dynamics.
Finally, I will discuss, in a more general context, applications of UTEM in the fields of ultrafast structural dynamics [5] and in the coherent optical control of free-electron states [3,6].