Speaker
Description
The beamline for advanced dichroism experiments (BLADE) is a soft x-ray beamline at the UK synchrotron facility Diamond light source. It delivers soft x-ray beam in the energy range from 0.4 to 1.6 keV. This energy range is optimized for the dipolar transitions of 3d transition metals (L$_{2,3}$ edges) and rare earth elements (M$_{4,5}$ edges). So the absorption effect benefits from a strong resonance and directly probes the electronic states responsible for magnetism.
The dichroic effect is measured as difference between circular polarization with opposite handiness in absorption. The absorption is detected by measuring the total electron yield (drain current) and fluorescence signal (photodiode facing the sample) simultaneously.
The absorption branch of BLADE is equipped with superconducting split pair coil that can deliver the magnetic field up to 14T. The sample can be cooled by a variable temperature insert down to 3K. The set up is complemented with an electromagnet providing the magnetic field up to 1.5T. This end station is using a Janis cryostat with the base temperature of 20 K.
In several examples, we demonstrate the capabilities of XMCD and how it can be applied to different magnetic systems.
As x-ray magnetic circular dichroism (XMCD) is a resonant effect, the technique is element selective. In a system as high entropy alloy with 5 magnetic elements, the use of this technique is essential to separate their contribution.
Furthermore, the intensity of the dichroism can be recorded as a function of the external magnetic field. Effectively, this provides element sensitive hysteresis loops that can disentangle elemental contributions to a complex magnetic behavior. We recorded the element specific hysteresis loops in exchange spring multilayers and with help of micromagnetic simulation understood the reversal process of these systems.
Spinel ferrites nanoparticles show significant difference in the surface structure compared to the bulk. This modification also manifests in the redistribution of Fe cations in tetrahedral and octahedral sites. XMCD in combination with the semi-empirical quantum many-body program QUANTY has been used to determine the degree of inversion.
