X-ray Magnetic Circular Dichroism (XMCD), which exploits the differential absorption of left and right circularly polarised X-rays by a magnetic material, has developed into a workhorse technique in modern magnetism research. Thanks to its inherent element selectivity, ability to probe very small sample volumes and extreme sensitivity, combined with the unique possibility to determine spin and orbital magnetic moments separately, this technique is providing previously unattainable insights into the microscopic origin of magnetism.
However, a large number of outstanding XMCD results are difficult to compare with macroscopic data, often obtained on different samples and under different experimental conditions. To address this challenge, researchers from TU Darmstadt and the University Duisburg-Essen in Germany, along with the ID12 team, have initiated a project dubbed “ULMAG – Ultimate MAGnetic characterisation”, which aims to develop a unique experimental setup by combining synchrotron- and laboratory-based techniques.
As part of the ULMAG project, which is funded by the German Federal Ministry of Education and Research, a new instrument for advanced magnetic studies has been developed, based on the high-field XMCD end-station installed at beamline ID12. It offers the unique possibility to measure (under strictly the same experimental conditions) the element-specific magnetic properties with XMCD and the magnetic stray field produced by the sample; the parallel and perpendicular magnetostriction; magnetotransport and caloric properties of a bulk magnetic material as a function of magnetic field (up to 17 T) and temperature (5–325 K).
The performance of this new instrument is illustrated with a case study of a nearly equiatomic FeRh alloy across the first-order magneto-structural transition (Figure 1). The field-induced changes observed in perpendicular magnetostriction or in Fe and Rh magnetisations probed with XMCD do not necessarily follow that of the macroscopic magnetisation. These results can lead to a better fundamental understanding of the mechanism of the magnetic transitions, which is key for designing new materials for more energy-efficient magnetic devices.
This instrument was built as a prototype of a more advanced and fully dedicated setup based on a 7-Tesla split-coil superconducting magnet. Admittedly, the split-coil magnet has a lower maximum field, but it offers the advantage of being able to accommodate a 2D detector for X-ray single-crystal or powder diffraction measurements. This setup is now under commissioning and can be used to study any type of magnetic transition with a strong interplay between magnetic, structural and electronic subsystems giving rise to a new functionality, e.g., a magnetocaloric effect. This new instrument is now open to all ESRF users and will serve as a unique and versatile tool to decipher the underlying physics of a broad range of magnetic materials from paramagnetic systems to hard permanent magnets.
Principal publication and authors:
Simultaneous Multi-Property Probing During Magneto-Structural Phase Transitions: An Element-Specific and Macroscopic Hysteresis Characterization at ID12 of the ESRF,
A. Aubert et al.,
IEEE Transactions on Instrumentation and Measurement, 71, 1-9, 6002409 (2022);