Precision magnetometry using photoelectrons' spin The picosecond time domain and milli-electronvolt energy range is crucial to decipher the physical processes that cause magnetic order and magnetisation reversal. EU-funded researchers built an experimental station for such precision magnetometry. Industrial Technologies © Shutterstock The EXSTASY (Experimental station for the analysis of the spin dynamics) project utilised for the first time the brilliance and energy tunability of free-electron lasers to analyse the magnetic properties of solids. In particular, Mott scattering detectors helped analyse the precession of the magnetisation vector at femtosecond time scale. Mott scattering detectors are widely used in combination with electron energy analysers to link spin data with the photoelectron energy spectrum. Funds from the EC’s Seventh Framework Programme (FP7) were earmarked for the new instrument that is hosted at Nanoscience Foundries and Fine Analysis (NFFA) – Trieste laboratory in Italy. This instrument supports analysis of the magnetisation vector with femtosecond time resolution and chemical selectivity. It is a unique tool at the disposal of European researchers for investigating the magnetisation dynamics in materials of interest for magnetic data storage. The engagement of a world-leading expert in Mott scattering detector design from the Saint Petersburg Polytechnical University in Russia was critical towards overcoming the technical and scientific challenges. EXSTASY researchers modified an existing Mott scattering apparatus and in particular, the electrostatic accelerator and beam splitter as well as the detection system. Efficient extraction of electrons from samples was addressed and a new mode of operation was added to the detectors. They built a dedicated ultra-high vacuum chamber to host the new polarimeter. Using the new Mott polarimeter system, researchers studied the hysteresis of iron films evaporated on gallium arsenide. The current set-up is designed for static measurements of spin polarisation. It is, however, the starting point for the implementation of a time-resolved polarimeter suitable for exploiting the single-pulse-data-acquisition mode made possible by free-electron lasers. EXSTASY was one of the first projects that focused on fast laser-induced magnetisation dynamics. Free-electron lasers open new paths for the investigation of the physics of solids, a field that remains largely unexplored. Developing experimental techniques to investigate the magnetic properties of solids, solid surfaces and nanostructures at free-electron laser facilities should help change the status quo. Keywords Precision magnetometry, EXSTASY, free-electron lasers, Mott scattering, magnetic data storage, polarimeter
