Periodic Reporting for period 1 - FASTMAGNETS (Ultrafast Demagnetization Dynamics Using Novel Table-top X-ray Source) Reporting period: 2018-09-01 to 2020-08-31 Summary of the context and overall objectives of the project The two-year MSCA project consists mainly of an experimental work on implementing novel soft X-ray beamline for magnetization dynamics studies. The experimental work has been performed in tight collaboration with three partner institutions. One of the most intriguing questions in the field of ultrafast magnetism is what is the fundamental speed limit for demagnetization (“erasing”) or magnetization switching (“writing”). The objective of this project is to address three fundamental questions in the field of ultrafast magnetization dynamics:1) how fast can a magnetic sample be demagnetized when heated by an ultrashort laser pulse?2) how fast can the magnetization component of a device be switched by an oscillating electromagnetic field?3) what is the mechanism behind the ultrafast laser-induced demagnetization?We are tackling these three questions using using an optical pump – X-ray probe techniques. The short pulse duration of the femtosecond table-top source provides us with temporal resolution down to 5 femtoseconds (fs) that can potentially be extended to attosecond range. Moreover, the next step is to simultaneously probe demagnetization dynamics of multi-element samples in the form of alloys and multi-layer samples. The proposed experiments were performed at University of Geneva (UniGe), Applied Physics Group (GAP) as well as in collaboration with two partner institutions: ETH Zürich, department of physical chemistry and photonics institute of Vienna University of Technology. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far The project addressed the objectives by performing the experiments as envisioned in the work packages of the proposal and in addition, performing related measurements that complement the knowledge in cases where this was more relevant as the project progressed. Namely, these measurements have been performed as envisioned in the work packages:* Measurements of wavelength scaling of magnetization dynamics of the cobalt (transient metal material) sample. The measurements were performed in part by the applicant in collaboration at INRS-EMT in Canada.* Implementation of a unique beamline for the small angle magnetic scattering at rare-earth composite materials harnessing the ytterbium laser technology developed at TU Vienna.* In collaboration with ETH Zürich, a soft X-ray transient absorption beamline was implemented at the host institution of UniGE paving the way for studying dynamics in nano-magnets and their interaction with the environment.One of the goals of the project is to study wavelength dependence of demagnetization dynamics in transition-metal samples. Up until now the vast majority of femtosecond magnetization studies have been performed using laser pulses in the NIR range, typically derived directly from a Ti:Sapphire laser amplifer centered at 800 nm. In our experiment the magnetization quenching was induced with pump pulses of three different wavelengths: 400 nm, 800 nm, and 1800 nm. This unprecedently large range of pump pulse wavelengths spanning from UV to mid-IR ensure high measurement precision and capture the underlying processes. We found that longer wavelength light quenches the demagnetization more efficiently in ferromagnets due to the higher electronic temperature and the wavelength scaling of the ponderomotive electron energy.The other goal of the project is to truly exploit the element-sensitivity of the X-ray probing for studying composite-element materials. Time-resolved X-Ray techniques provide insights into spin changes with elemental-specificity on their natural spatial and time scales. The broad spectral bandwidth of the HHG spans the characteristic M- and N- absorption edges of the transition metal (TM) and rare-earth (RE) elements that exhibit magneto-optical activity. Despite the numerous proof-of-concept demonstrations using HHG sources, all of the previous studies were focused of the TM ferromagnets. The recent developed magnetic nano-structure materials are based on rare earth (RE) associate ferrimagnetic/multiferroics multicomponent systems, which are promising candidates for the future storage and information processing spintronic devises, owing to their nanometer size, fast speed, efficient driving dynamics, and topological protected stability. We demonstrate, for the first time, time-resolved X-ray resonant magnetic scattering (tr-XRMS) measurements on the inner-shell 4f-electron from a prototypical rare-earth (RE) composite ferrimagnetic system CoTb (Tb N-edge at 155eV), by using a bright HHG source. The tr-XRMS is enabled by direct driving HHG process with a power-scalable, high-energy Yb laser technology. The fully phase-matched broadband plateau (>200 eV) of the helium HHG with a record photon flux completely covers the desired resonant energy range of RE’s N-edges with <20 fs temporal duration.Furthermore, project accomplished also a broader goal of utilizing the X-ray measurement techniques based on table-top laser-based sources for studying ultrafast processes in materials. We have demonstrated the first X-ray transient absorption (XAS) measurement in the water-window spectral range (284 - 538 eV) of a solution sample using a table-top HHG source by integrating it with a sub–micrometer–thin flat liquid jet. These measurements represent the first extension of table-top XAS to the oxygen edge of a chemical sample in the liquid phase. Using a soft X-ray beamline implemented at UniGE, we were able to temporally resolve the transient absorption features at the carbon K-edge of ethanol and methanol during strong–field ionization, which trace the valence-shell ionization dynamics of the liquid alcohols with a temporal resolution of ∼30 fs. These liquid-phase measurements will allow implementing studying magnetization dynamics in the magnetic nanoparticles and their interaction with the liquids in the future. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The work contributed to the development of new techniques and studying new physics. In terms of methodology, the key achievements are:* Contributed to the implementation of a resonant X-ray magnetic scattering beamline in INRS-EMT in Canada for transition metal based magnetic material measurements.* Envisioned and implemented an efficient table-top soft X-ray source in the 150-200 eV spectral range with record-high photon flux using laser technology developed with a partner institution of TU Vienna.* Implemented a water-window transient-absorption beamline for liquid-phase and solid-state measurements at UniGE.The key achievements in advancing the physics:* Revealed the wavelength-scaling of ultrafast magnetization quenching in transition metal multilayer sample and the influence of the electronic system temperature on the speed of the process* Measured the two time constants of magnetization quenching in terbium-cobalt ferrimagnetic system by element-selective probing at the N absorption edge of terbium* Demonstrated the nuclear dynamics in a liquid sample revealed using transient-absorption in the water-window spectral range.Through the collaborations of the two partner institutions, the PI has expanded his network of collaborators and which will make him more independent and prove his ability to perform original research in different research environments. Having the experience in applying for the MSCA fellowship he gained invaluable experience and skills in applying for his own funding that will help fund his future research through national and international funding schemes. summary-logo.png
