Neutron diffraction under high magnetic fields

Magnetic phase transitions are strongly related to changes of structure, for which neutron diffraction is the most powerful and most direct observation method. In order to investigate magnetic phase transitions in high fields by neutron diffraction, we have been developing a technique to combine pulsed fields up to 20 T with the spallation neutron source at KEK. It is now possible to observe magnetic scattering in fields higher than those obtained using conventional superconducting magnets. This technique has been applied to determine magnetic structures of the complicated metamagnetic materials, PrCo2Si2 and DyAg in fields above 10 T. A phase transition observed at 12.5 T in CsCuCl3 has been confirmed to be due to quantum effects.