X-Treme / X07MA: X-ray absorption spectroscopy at high magnetic field and low temperature
The X-Treme beamline, run by the Microscopy and Magnetism Group, produces a high flux of soft x-rays with variable polarization (circular left, circular right and linear polarization in any angle between 0 and 90 degrees) from an Apple-II undulator source.
The end station is equipped with a superconducting 2D vector magnet operating at 7 T single direction or 2 T vectorial field and a 2 K sample insert. The end-station is also equipped with an in-situ sample preparation system and a variable-temperature scanning tunneling microscope. In order to prepare for their experiment, users are asked to look at the end-station webpage, at the user information webpage and at our frequently asked questions section.
The beamline mostly focuses on measurements involving x-ray magnetic circular and linear dichroism at transition metal L2,3-edges (transition 2p -> 3d), lanthanide M4,5 edges (transition 3d -> 4f) and oxygen or nitrogen K-edges (transition 1s -> 2p). Typical systems studied are single atoms on surfaces; molecules or single-molecule magnets in bulk or on surfaces; superlattices and ultra-thin films. Different detection modes are available: total electron yield, total fluorescence yield, transmission and x-ray excited optical luminescence.
The X-Treme beamline and end station were constructed by a consortium including PSI (Microscopy and Magnetism group, SLS) and the group of Prof. Harald Brune, Laboratory of Nanostructures at Surfaces at EPFL. The funding for the beamline construction was provided by PSI and the one for the end station from the EPFL and the Swiss National Science Foundation.
|Energy range||400-2000 eV|
|Flux (700eV)||4 x 10^15 photons / s / 0.1%BW / 0.4 A
typically 10^12 photons / s at sample position (0.1 eV energy resolution, 700 eV photon energy)
|Focused spot size||exit slit µm x 230 µm (V x H)|
|Spectral resolution||> 5000|
|Polarization||Linear: 0 deg (horizontal) to 90 deg (vertical)
Circular: right / left
Current Highlights and News
Photoswitching in a Molecular Cube
Niéli’s paper is accepted in the Journal of Physical Chemistry Letters! We use X-ray absorption spectroscopy and X-ray magnetic circular dichroism to watch directly how the Co and Fe ions in a molecular cube change their oxidation states and turn from diamagnetic into paramagnetic units upon light irradiation.
New Method for Calculating Soft X-ray Magnetic Circular Dichroism Spectra
Scientists have demonstrated in a combined theoretical and experimental effort that the new ligand-field density functional theory method (LF-DFT) can be used to calculate the X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism (XMCD) of lanthanide compounds from purely structural input.
Revealing a Living-Dead Magnetic Layer
A peculiar magnetic “dead layer” is detected at the surface of thin films of DyTiO3, a ferrimagnetic Mott insulator. Depth dependent X-ray absorption measurements performed at the X-Treme beamline in the Swiss Light Source indicate that this layer is associated with a deviation of the Ti valence from 3+ toward 4+ at the film surface, suppressing the magnetic coupling between Ti ions and unleashing a strong paramagnetic response from uncoupled Dy ions.