Into the fourth dimension: time-resolved soft X-ray laminography

Three-dimensional magneto-dynamical processes have recently attracted much attention in the condensed matter research community thanks to their predicted rich dynamical behavior and novel functionalities. However, their experimental investigation has, so far, only relied on indirect characterizations, due to the lack of an imaging technique able to resolve their dynamics not only in time, but also along all three spatial dimensions.

In the work presented in this highlight, researchers from PSI, in collaboration with German and British institutes, combined pump-probe STXM imaging with soft X-ray magnetic laminography imaging to obtain a time-resolved imaging technique able to resolve magnetization dynamics in four dimensions, i.e. in time and in all three spatial dimensions. Thanks to the use of an avalanche photodiode as X-ray detector, it is possible to investigate excitations with arbitrary frequencies, overcoming the major limitation for time-resolved imaging of three-dimensional techniques where the acquisition of the single projections relies on two dimensional X-ray detectors, such as e.g. ptychography.

The dynamics of two different excitation modes of a ferromagnetic CoFeB microstructure, namely a domain wall excitation mode (occurring at 913 MHz) and the fundamental magnetic vortex gyration mode (occurring at 326 MHz), were investigated with this technique. In particular, the vortex gyration mode exhibited a rich three-dimensional dynamical behavior and the researchers were able to identify the coexistence of a breathing mode with the vortex gyration mode, providing a first three-dimensional view of such a dynamical mode in thick magnetic microstructures.

Thanks to the possibility of freely selecting the excitation frequency, soft X-ray magnetic laminography will allow for the investigation of resonant magneto-dynamical processes in four dimensions, providing a leap forward in the experimental investigation of three-dimensional magnetic systems.