7 Tesla magnet

This custom build magnet was designed especially for soft x-ray XMCD measurements. The magnetic field of 5 Tesla can be ramped up relatively fast (3 Tesla in 1 minute). The sample is vacuum-mounted onto a LHe variable temperature insert that can reach 7-10 K depending on configuration. This insert can be rotated over 360 degrees. The sample space is ultra-high vacuum, obtained by cryo-pumping of the liquid helium can without bake out.

XMCD spectra can be simultaneously measured in drain current and fluorescence yield mode, and if requested in transmission. At the moment the XMCD sensitivity is about 1%. In order to get good data the edge jump should be at least 30%.

Samples

Samples need to have a minimum 4x4 mm measurement surface, for smaller sizes contact us in advance. Polycrystalline samples need to be 3 mm thick so that they can be filed in vacuum to expose clean surfaces. Single crystals that need to be fractured in vacuum need to be 5 mm high. Single crystals that need to be sputter-cleaned can have up to 10 mm diameter, and be typically 2-3 mm thick.

Sample surfaces can be prepared in a UHV chamber below the magnet. Up to 3 samples are loaded into this chamber on a magazine. They are transferred into the magnet with a vertically mounted magnetic transfer rod. The preparation chamber can be equipped with various surface preparation tools, such as

• diamond file scraper for poly-crystaline samples
• cleaver for single crystals
• sputter gun sample and heater stages (up to 300 K for annealing in gas atmospheres, up to 1000 K for single crystals)
• Omicron e-beam evaporators and Knudsen cells with quartz crystal rate monitor

Unfortunately electron spectroscopy and diffraction equipment can not be used due to the high magnetic stray field produced by the magnet.

We have developed a range of sample holders in high-purity aluminum. Samples can be glued or clamped down. A special holder for single crystals is available. Sample size can be anything between 2 mm and 15 mm.

Scanning tunnelling microscopy (STM) option

This system can be extended with the surface science preparation chamber and Omicron variable temperature STM. The preparation chamber gives access to a LEED/AES system, sample ion sputtering, annealing up to 1000 K and 2 independent Omicron electron beam evaporators. For more details please contact us.

Safety Aspects

A cryomagnet is potentially dangerous. Be aware of the strong forces exerted by the magnet on any steel parts that are kept within 50 cm from the bore. Before switching on the field always clean up your workspace. Take extra care to lock the magnetic transfer rod in its lowest position, and above all do not change samples with field on or disaster will result.

Be carefull when handling helium. There is serious risk of freezing and suffocation. If ever the magnet quenches it blows of tens of cubic meters into the hutch. When oxygen levels drop you will faint without prior notice.