Final Report Summary - IMAGINE (Imaging Magnetism in Nanostructures using Electron Holography)
The aims of this project were to develop advanced characterization methodologies for the quantitative characterization of magnetic spin structures in nanocrystals that have sizes of below 20 nm in the transmission electron microscope. Key experimental achievements have included the quantitative mapping of temperature-dependent magnetism in magnetite nanocrystals in minerals, studies of the influence of oxidation on the magnetic microstructure of individual magnetite nanocrystals, the mapping of magnetic states in novel magnetic gyroid structures, magnetic nanotubes, defective and elongated biogenic magnetite nanocrystals and electrodeposited magnetic nanowires containing different magnetic underlayers. There has been important progress in the use of off-axis electron holography in the study of the temperature and magnetic field dependence and geometric confinement of skyrmions in nanofabricated structures and thin films, the experimental discovery of chiral bobbers coexisting with magnetic skyrmions, the application of field cooling and zero field cooling to individual magnetic nanostructures in situ in the transmission electron microscope and mapping of the magnetic fields of electrical currents in nanoscale circuits. Significant progress has also been made in the development of electron magnetic circular dichroism in a chromatic aberration corrected transmission electron microscope for magnetic characterization in oxides with atomic spatial resolution, as well as in the development of in-plane electron magnetic circular dichroism. Methodological progress includes the successful development of algorithms and software for model-based vector field tomography, the demonstration of 0.5 nm spatial resolution for electron holography in magnetic-field-free conditions, the development of high-frequency double-exposure electron holography for ultrafast studies of magnetic switching processes and experiments aimed at shaping electron beams using electric fields, phase and amplitude masks and hardware aberration correctors and their application for the characterisation of magnetic properties in materials. Instrumental developments include novel in-plane-magnetizing and high-frequency specimen holders for magnetic switching studies, improvements and the use of new hardware to achieve ultra-fast electron tomography combined with electron holography for the sub-10-s acquisition of full tomographic tilt series of electron holograms for studies of dynamic processes in materials. 69 papers have been published during the project and three patents have been filed based on new phase plate technologies and new approaches for shaping and accelerating electron beams. Key publications include papers in Nature Materials (1), Nature Nanotechnology (1), Nature Communications (6), Nature Scientific Reports (7) and Science Advances (1).