Pulsed High Magnetic Field Neutron Scattering – MAGFINS

One subject of primary interest in fundamental physics is the study of quantum correlation effects in condensed matter. Intensive research on advanced materials has led to the discovery of new compounds with spectacular properties driven by strongly correlated electrons. High magnetic fields allow to finely tune the delicate balance between different correlation effects. The ability to study these materials under such extreme conditions is therefore of fundamental importance. Neutron diffraction has complementary features to X-ray diffraction, and unique capabilities for studying magnetic ordering of materials. The precise knowledge of the magnetic structures is a prerequisite to describe and understand the key parameters of a material. Neutron scattering has so far been combined only with moderate steady magnetic fields and many materials have been studied with this technique. At present no neutron facility can offer magnetic fields higher than 17 T to its users.

Within this ANR project we propose to develop single-crystal neutron diffraction under intense pulsed magnetic fields up to 40 T, with pulse lengths of the order of 100 ms. This proposal originated from the first successful experiments combining pulsed magnetic fields (up to 30 T) and neutron diffraction. These experiments were carried out at the ILL by using coils of the size of a 2-Euro coin (built at the Institute for Materials Research, Sendai, Japan) installed inside a standard orange-type helium cryostat. These two pioneering experiments, to which the laboratories signing this proposal have contributed, showed the feasibility of the technique. However they also clearly demonstrated the necessity of improving the duty cycle of the magnetic field experiment, in particular by increasing the duration of the pulse by at least an order of magnitude. Obviously, such an improvement demands a major change in technology.

Here we present a proposal for the design, the construction and the use of a complete pulsed-field apparatus, including a pulsed field coil with the highest possible duty cycle and a cryogenic sample environment. This device will produce longer pulses, which will have the advantages to limit eddy-current heating and coil fatigue. In the meantime, the neutron spectrometer will be equipped with efficient focusing neutron optics and a new fast (high counting rate) detector adapted both to the time structure of the magnetic-field pulses and the larger available sample volume and flux. We then intend to combine this pulsed-field apparatus with well-established neutron-scattering techniques, such as single-crystal diffraction (first) and white-beam Laue diffraction (in a further step), with the final aim to investigate the effects of the magnetic field on several strongly correlated electron systems or quantum magnets.

The project proposed here combines the skills in the generation of intense pulsed magnetic fields, low-temperature sample environment, high intensity neutron diffraction and finally in the physics of solid state magnetism. To that end, the complementary expertise of four different worldly-recognized laboratories is essential, namely the Toulouse High Magnetic Field Laboratory (LNCMI, CNRS-Toulouse), the Neutron Diffraction Laboratory (INAC/SPSMS/MDN, CEA-Grenoble), the Institut Laue Langevin (ILL, Grenoble) and the Institut Néel (IN, CNRS-Grenoble).
A successful realisation of the project, aiming to offer the possibility of performing neutron diffraction measurements under pulsed magnetic fields up to 40 T on the best neutron source worldwide, will allow maintain the ILL neutron user’s community in the race after the completion of the Japanese, American and German high-magnetic-field projects, before the implementation on the ESRF and ILL site of the dc facility currently under consideration.