"X-ray Studies of Materials in High, Pulsed Magnetic Fields"

Dr. Zahir Islam, Argonne National Laboratory

High-field pulsed magnets for synchrotron x-ray applications are not the solution to all materials problems requiring high magnetic fields, but they are the only approach to studies of materials in “extreme conditions.” Design flexibility of magnet coils to take advantage of specific x-ray-scattering cross section and the possibility to produce fields in the range of 50-100 Tesla make pulsed magnets quite desirable. Furthermore, by combining pulsed magnetic fields with the natural timing structure of synchrotron radiation, structural and magnetic effects should be detectable on the microsecond to millisecond levels with the possibility of pushing the temporal resolution to a faster timescale, potentially ushering in studies of field-induced “non-equilibrium” phenomena, which lie outside the realm of DC magnets. Recently, an extremely high-field pulsed magnet system has been developed for synchrotron x-ray scattering and spectroscopy studies of materials at the Advanced Photon Source (APS), which is a unique capability in the United States. Pulsed magnetic fields (1-5 ms in duration) are generated by discharging a configurable bipolar capacitor bank (3kV, up to 4.5 mF) into the magnet coils.  These low-energy small-bore coils (Tohoku design) are mounted on the cold finger of a closed-cycle He cryostat capable of a repetition rate of ~10-20 minutes for peak fields in the range of 20-30 Tesla. Time-resolved scattering data are typically collected using a combination of fast APD detector, a multi-channel scaler, and a high-resolution digital storage oscilloscope, respectively. Currently, 30 Tesla split-coil magnets are being used in structural studies of geometrically frustrated magnetic compounds, results of which are presented. Future opportunities of experiments in high-field pulsed magnet are discussed.

Use of the APS is supported by the U. S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.