X-ray magnetic holography in reflection geometry

In recent years X-ray magnetic holography has attracted interest as a complementary technique for lensless nanoscopic imaging of magnetisation domains in continuous and structured thin films. Essential for the holography is that the imaging of the magnetisation can be performed not only in the remanent state (as is typical for domain characterization using e.g. PEEM and MFM), but also over the full range of the applied field. This has been a great advantage in the opportunity to study the evolution of the magnetic states and thus to explore a range of the intrinsic properties of magnets. Due to the nature of the experiment, which is performed in transmission geometry, imaging is however limited only to 'out-of-plane' components of the magnetization. If the magnetization is in-plane, as is normally the case for thin film structures, the imaging is inhibited due to the vanishing XMCD effect. This restricts the application of the technique to only a single geometry.In this project we intend to overcome the limitation of x-ray magnetic holography by proposing a novel 'reflection' geometry of the technique, which allows us to image samples that have 'in-plane' magnetization. To implement this geometry we will modify the structure of the sample that will suit the scattering reflectivity experiments. In particular, we will introduce reflective 'pins', which will serve as reference 'holes' in the transmission experiment. Both reflective pins and the object will be placed on a transparent SiN membrane to allow the scattering from the background to be minimised. As part of this experiment it is also intended to explore a new design of the sample, in which the surrounding background of the observed object is removed by FIB milling. This will help significantly to improve the expected signal/noise intensity ratio. An added bonus of using SXRMS holography is the element selectivity. The imaging can be performed for different materials comprising the same macroscopic volume. For instance, in the case of a multilayered system (such as GMR devices with two different magnetic layers) the imaging can be obtained simultaneously for several layers, hence giving the opportunity to study the relation of the different magnetic moments in neighbouring layers.

The proposed X-ray holographic technique would directly benefit scientists working with nanostructured magnetic materials. Imaging magnetisation with nanoscopic resolution combined with the option of the applied magnetic field (which is crucial for magnetic research and applications, but not available in techniques, such as XPEEM and MFM) will enable access for other scientists working in this field. There is a number of scientists in UK and our European collaborators who are interested in using magnetic holography and who see the proposed instrument directly benefiting in their own research. Long-term benefits are expected from the results obtained in the studies of novel technological materials. The holographic imaging techniques would also be suitable for nonmagnetic materials which would benefit either from the particular configuration of the setup (reflection, transmission) or the particular environment available for the host end-stations (e.g. energy band, brilliance). In each case the use of the proposed techniques will enlarge the user community working in the areas of nanotechnology. The project indirectly reflects the main strategy of STFC to develop world-class facility for innovative research in the fields of science and technology. It is also aligned with the main objectives of the Diamond Facility Roadmap, which identifies the 'maintaining access to leading edge experimental facilities' as a key element of keeping UK scientists at the forefront of their research. In particular, the new techniques, when developed at Diamond, will provide access for experiments in a wide range of novel magnetic materials strategically and technologically important in the progress of magnetoelectronics. We also believe that the project fits perfectly with the facilities (SSRL and Diamond) strategies for technology development. The type of materials considered in the project targets the main technological applications currently developed by industry and academic institutions. The project offers excellent opportunity for developing collaborative links between Exeter and SSRL. For the PhD student, for whom this will be a first experiment at synchrotron facilities, this visit will provide an ideal training experience. Mr Duckworth's topic of his PhD project is directly related to X-ray magnetic holography. Participation in such experiments is essential for him to obtain both data and the necessary expertise in order to complete his PhD studies.