The real-space spin texture and the relevant magnetic parameters were investigated for an easy-axis non-centrosymmetric ferromagnet Cr11Ge19 with Nowotny chimney ladder structure. Using Lorentz transmission electron microscopy,we report the formation of bi-Skyrmions,i.e., pairs of spin vortices with opposite magnetic helicities. The quantitative evaluation of the magnetocrystalline anisotropy and Dzyaloshinskii-Moriya interaction (DMI) proves that the magnetic dipolar interaction plays a more important role than the DMI on the observed bi-Skyrmion formation. Notably, the critical magnetic field value required for the formation of bi-Skyrmions turned out to be extremely small in this system, which is ascribed to strong easy-axis anisotropy associated with the characteristic helix crystal structure. The family of Nowotny chimney ladder compounds may offer a unique material platform where two distinctive Skyrmion formation mechanisms favoring different topological spin textures can become simultaneously active.
Reference: R. Takagi et al, Physical Review Letters 120, 037203 (2018)
Dr. Yasin Ekinci, Head of the Advanced Lithography and Metrology Group and ad interim Head of the Laboratory for Micro and Nanotechnology, has been elected to the grade of Fellow of The International Society for Optics and Photonics (SPIE).
On 1st January 2019, the European Horizon 2020 project BEAmline for Tomography at SESAME (BEATS) was launched with the objective to design, procure, construct and commission a beamline for hard X-ray full-field tomography at the SESAME synchrotron in Jordan. The European grant is worth 6 million euros and will span a four-year period from beginning 2019 to end 2022.
A major milestone in the commissioning of SwissFEL has been reached: the first pump-probe experiments on proteins have been successfully carried out. Crystals of several retinal-binding proteins were delivered in a viscous jet system and a femtosecond laser was used to start the isomerization reaction. Microsecond to sub-picosecond snapshots were then collected, catching the retinal proteins shortly after isomerization of the chromophore.
The Innovation Award on Synchrotron Radiation 2018 went to Dr. Christian David, also from the Paul Scherrer Institute, and to Prof. Alexei Erko, who recently moved from the HZB to the Institute for Applied Photonics (IAP) in Berlin-Adlershof.
21 November 2018
Helping chemists to understand degradation and stabilization of catalytic nanoporous gold structures
It is difficult for X-rays to compete in spatial resolution with electrons, but they can probe relatively large bulk sample volumes at atmospheric pressure in a non-destructive manner. This makes X-ray tomography a promising tool to investigate catalytic nanoporous materials under real operating conditions. In this work researchers from Karlsruhe Institute of Technology and the University of Bremen in Germany compared X-ray ptychographic tomography, electron tomography and focused ion beam-scanning electron microscopy performed on a nanoporous sponge-like gold material with numerous applications, including selective oxidation and sustainable production of chemicals. As it turns out, the X-ray based method is the most suitable for in situ or sequential post-mortem analysis of volumes after thermal annealing, which researchers want to pursue in the future.
The first SwissFEL call for proposals took place, deadline for submission was the 15th of September. In this first call for proposals SwissFEL received overwhelming interest from the user community. A total of 47 proposals were submitted for the SwissFEL Alvra experimental station and 26 for the Bernina experimental station. The Proposal Review committee PRC took place on 18-19 October 2018. Due to the early operation phase of the facility only a reduced number of user shifts is available, resulting in SwissFEL being overbooked by a factor of 10 and an extremely strong competition for beamtime.
PSI researchers have developed an experimental chamber in which they can recreate atmospheric processes and probe them with unprecedented precision, using X-ray light from the Swiss Light Source SLS. In the initial experiments, they have studied the production of bromine, which plays an essential role in the decomposition of ozone in the lower layers of the atmosphere. In the future, the new experiment chamber will also be available for use by researchers from other scientific fields.
Snapshots of bacteriorhodopsin
Bacteriorhodopsin is a membrane protein that harvests the energy content from light to transport protons out of the cell against a transmembrane potential. Nango et al. used timeresolved serial femtosecond crystallography at an x-ray free electron laser to provide 13 structural snapshots of the conformational changes that occur in the nanoseconds to milliseconds after photoactivation. These changes begin at the active site, propagate toward the extracellular side of the protein, and mediate internal protonation exchanges that achieve proton transport.
Scintillator screen image showing both, the FEL radiation and the electron beam. The electron beam was separated from the FEL beam using a dipole magnet.
On the 15th of January 2014, first lasing was achieved in the SwissFEL injector test facility. This is a great success on the way towards SwissFEL, the future hard x-ray free-electron laser that is currently under construction at PSI. It proves the successful functioning of many key components together in a larger system as required for SwissFEL. Furthermore, this is the very first operation of a free-electron laser in Switzerland.
Since 2010, PSI has been operating a test facility to study and optimize the electron source for SwissFEL. Over the last years, the test facility was advanced to one of the most brilliant electron sources in the world, and during the last shutdown end of 2013, a first undulator - a highly precise periodic array of magnets - was installed in the facility. This innovative type of undulator is an in-vacuum design with a very small period length of only 15 mm, that was specifically developed for SwissFEL.
During the very first beam time after the installation of the undulator, the electron beam could be successfully tuned to pass the undulator with low losses - this is very important to prevent radiation damage to the sensitive 1060 permanent magnets of the undulator. The electrons generate spontaneous radiation when passing the undulator, and this radiation was detected with scintillator screen monitors. In a next step, the electron beam was strongly compressed in a bunch compressor chicane to generate a very large charge density, which is required for the FEL process. This initiated the free-electron lasing process, leading to an exponential increase of the emitted radiation along the undulator. An electron beam with an energy of 220 MeV and a bunch charge of 200 pC was used in that process, and first lasing was detected at a wavelength of around 80 nm. By adjusting the gap of the undulator, the wavelength of the emitted laser light could be tuned over one octave from around 45 to 90 nm
Facility: SwissFEL Reference: Hans Braun; firstname.lastname@example.org; Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland