Wide Aperture VEctor magnet for Neutron and X-ray scaTtering – WAVENEXT

The WAVENEXT project aims to study the magnetic anisotropy phenomena in epitaxial films using two techniques (neutron diffraction (ND) and soft X-ray resonant magnetic reflectivity (SXRMR)) giving access to magnetism on a microscopic scale. To make the most of these two powerful and complementary techniques, an important instrumental development is required: in order to better study the anisotropy phenomena, it is necessary to implement 3D vector magnets (capable of applying a magnetic field in any direction in space) on the ND and SXRMR instruments. Thus, the direction of application of the field and the act of putting the sample in diffraction / reflectivity conditions can be decoupled, which is not the case in existing devices.
The development of such magnets, which do not exist commercially, is now well advanced: We offer an innovative concept using only vertical axis coils to create a three-dimensional field. A patent has been filed and the technology transfer to the Sigmaphi company is currently underway. The two magnets will be delivered and operational during this project: the “neutrons” magnet (already ordered with partial funding from the Ile de France) in the beginning of the project in April 2017, and the "photon" version in september 2018. Three scientific areas have been defined in order to maximize the unique experimental tools available to us:
- Antiferromagnet spintronics. This is an emerging field of spintronics, in which antiferromagnetic films (magnetically ordered without resulting magnetization) are cast in an active role within the devices, as opposed to their complimentary functions today. Significant magnetoresistance effects have been reported recently, but the precise understanding of phenomena is lacking. This is largely due to the fact that the relevant parameters, including the antiferromagnetic ordering parameter and surface / interface of magnetization are difficult to measure. The two techniques that we use provide direct access to these quantities, and vector magnets allow us to reproduce in neutron beam or soft x-ray magnetic field sequences (including rotating fields) used in magnetotransport experiences.
- Materials with perpendicular magnetic anisotropy. This is a major issue electronic spin in recent years. The magnetization of most of the thin films lies in the plane of the layers, which is promoted by shape anisotropy. However, thanks to efficient interface engineering, it is possible to switch the magnetization of the ferromagnetic layers perpendicular to the plane of the films. This allows a significant improvement of device performance (storage density, efficiency of spin transfer, ...). However, some physical mechanisms of these systems are still poorly understood, preventing optimization. Allowing, for the first time, to apply a field perpendicular to the layer plane during a measurement of reflectivity, the WAVENEXT project will access the magnetization profile of these systems, often very complex. Neutron diffraction will see how the antiferromagnetic layers present in the system are affected.

- Electrical control of anisotropy. The two previous points consider systems where the magnetic anisotropy is a given. An emerging field of spintronics is to seek to control the anisotropy by a current when a voltage. In this case, we can expect the benefits of each type of anisotropy in a single system. The two magnets WAVE will be equipped so as to electrically connect the samples studied, and therefore observe under the beams of anisotropy induced changes.