“VEKMAG” at BESSY II creates 3D magnetic fields in samples
A general view of the VEKMAG end-station. The vector magnet chamber (grey) is supported by a hexapod frame. Below the magnet one can distinguish the detector chamber (green) and in the forward direction the deposition chamber (dark grey) is displayed. The beam quality is monitored by a diagnostic chamber (yellow) positioned in front of the magnet chamber. © Dr. Tino Noll
Together with HZB, teams from the Universität Regensburg, from the Freie Universität Berlin and from the Ruhr Universität Bochum have jointly set up a unique measurement station at BESSY II: a vector electromagnet consisting of three mutually perpendicular Helmholtz coils which enables setting the local magnetic field at the sample position to any orientation desired. The first measurements of magnetic materials, spin systems, and nanostructured magnetic samples are scheduled for early 2015.
“We have been working on this project for almost six years”, reports HZB physicist Dr. Florin Radu. He is coordinating the project with the three universities. The deposition chamber for the samples was designed at Freie Universität Berlin. Ruhr Universität Bochum built the detector chambers, and Universität Regensburg developed the concepts for synchrotron beam-based ferromagnetic resonance experiments.
Rapid change of polarisation
In the meantime, Radu and his team ensured optimum characteristics of a new beamline for carrying out most sophisticated experiments: “We need an extremely stable beam, but we also want to be able to change the polarisation of the x-rays very rapidly”, he explains. “For that reason, we developed a hexapod vacuum chamber with six moveable legs supporting a mirror. By changing the leg positions slightly, we can change the orientation of the first mirror and thereby the polarisation of the x-ray beam in just seconds – about one hundred times faster than before.” The tests show that this prototype arrangement improves the signal-to-noise ratio by a factor of more than ten.
Temperature between 1,6 K and 500 K
The new experimental station will not only facilitate many different kinds of studies, particularly in the soft X-ray region, but will also permit to carry out completely new studies that require temperatures of 500 Kelvin right down to 1.6 Kelvin and magnetic fields as high as nine tesla. Simultaneously the X-rays can penetrate the individual atoms and excite their outer electrons, enabling magnetic properties of the individual elements to be distinguished.
The main assets of the new VEKMAG end-station are experimental specifications that are unique in comparison with stations operating at other international facilities. In particular for element-specific and time-resolved measurements of ferromagnetic and paramagnetic resonances, as well as for spectroscopic and scattering experiments VEKMAG offers a unique sample environment. However, “VEKMAG will only attain its full potential, once HZB has implemented a new innovative beam filling pattern with variable pulse lengths at full photon intensities”, according to Radu, because “we can then investigate rapid spin dynamics with sub-picosecond time resolutions.”
The VEKMAG project was funded by the German Federal Ministry for Education and Research (BMBF) through a grant of about four million Euros.
- Magnon momentum microscopy: A new window into nanoscale spin-wavesAn international team lead by the Max Born Institute has developed a new type of momentum microscopy to image magnons — the quanta of collectively excited spins — directly in two-dimensional reciprocal space using soft X-rays. Measurements have taken place at BESSY II and PETRA III, first author ist the HZB physicist Steffen Wittrock. Owing to its remarkable sensitivity, simplicity, and access to nanometer-scale wavelengths, this novel technique establishes a powerful and versatile platform for exploring nonlinear magnon interactions, which are promising for future computing schemes.
- X-ray analysis reveals overpainted fascist symbolsErich Mercker was a successful painter during the Nazi era and in the years that followed. After 1945, he covered up Nazi symbols in at least one of his paintings. With an interdisciplinary team, physicist Dr Ioanna Mantouvalou reports on this study in the Nature Journal Heritage Science.
- Magnetic field during catalyst synthesis triples ammonia yieldApplying an external magnetic field during the synthesis of CoFe₂O₄ electrocatalysts triples the ammonia yield during electrocatalytic conversion. The magnetic field alters the surface states of the spinel oxide thin films, making catalytically active sites more accessible. In the journal 'Advanced Functional Materials', a team led by Marcel Risch at HZB and Sanjay Mathur at University of Cologne demonstrates a scalable strategy for developing next-generation electrocatalysts for efficient and sustainable chemical production.