Advances in neutron spectroscopy and high magnetic field instrumentation for studies of correlated electron systems

Neutron Spectroscopy has provided critical information on the magnetism in correlated electron systems. Specifically quantum magnets, superconductors, and multi-ferroics are areas of productive research. A discussion of recent measurements on the SEQUOIA spectrometer will provide examples of how novel instrumentation concepts are used on the latest generation of spectrometers to extend our knowledge in such systems. The now ubiquitous function of sample rotation allows for full mapping of volumes of Q and ω space. An instrument focused on low angles could extend these maps to cover more of the first Brillioun zone. Innovative chopper cascades allow two unique modes of operation. Multiplexed measurements allow the simultaneous measurement of high and low energy features in an excitation spectrum. Alternatively, by limiting the neutron bandwidth incident on the Fermi Chopper, background from subsequent time frames is removed; enabling the observation of weak, large energy transfer features. Finally the implementation of event-based detection for neutron experiments is essential for time correlated experiments. Diffraction studies of the high field spin states in MnWO4 using magnetic fields up to 30 T, provided by a pulsed magnet, illustrate this method. Expanding the high field studies to spectroscopy will require a novel instrument, focused around a world class DC magnet, like Zeemans proposed for the SNS.