Jiefeng Cao

The performance of synchrotron beamlines critically depends on the optimal coupling between the undulator and the monochromator. This work presents the implementation and quantitative characterization of a synchronized scanning system for the elliptically polarizing undulator (EPU) and the variable-line-spacing plane-grating monochromator at the BL07U beamline of the Shanghai Synchrotron Radiation Facility (SSRF). The system ensures that the monochromator’s narrow bandwidth dynamically tracks the brilliant central cone of the undulator radiation. A linear correlation between the monochromator energy and the undulator gap, justified theoretically for small scan ranges and reinforced by a robust real-time calibration procedure, forms the control basis. The automation is built upon a standard software stack comprising EPICS for device control, the Bluesky Suite for experimental orchestration, and Phoebus for the human–machine interface. Through comparative X-ray absorption spectroscopy (XAS) measurements at the Fe L_2,3-edges, the synchronized mode is shown to enhance beam brilliance by 37% and stabilize the incident flux, reducing its variation from 4.2% to 1.8%. This directly results in absorption spectra with superior lineshape fidelity, a 40% reduction in noise, and the elimination of pre- and post-edge artifacts, unequivocally isolating the synchronization effect. This advancement provides a stable, high-brilliance photon source essential for high-quality XAS and X-ray magnetic circular/linear dichroism (XMCD/XMLD) studies.

Tantalum (Ta), which is widely used as a spin sink material, especially for its β-phase with strong spin-orbit coupling (SOC) exhibits a high spin-charge interconversion efficiency. In this work, we investigate the spin-to-charge conversion (SCC) process of Ta/Permalloy (Ta/Py) bilayers with Ta having different crystalline phases. The structural phase transition of Ta film from tetragonal to body-centered cuboidal (BCC) which corresponds to β- and α-phases was obtained via high-temperature annealing in vacuum atmosphere. By applying ferromagnetic resonance (FMR) and inverse spin Hall effect (ISHE) measurements, the measured spin mixing conductance and SCC DC voltage show a strong correlation with the crystalline phase of Ta thin films in Ta/Py bilayers. A significant enhancement of spin mixing conductance in (β + α)-Ta/Py has been found and a higher SCC DC voltage was detected for α-phase Ta film with a weak SOC than β-phase Ta film with a strong SOC. These results reveal the significant role of the interfacial constitution in heavy metal/ferromagnet bilayers for spin current transportation, which can promote the development of high-efficiency spin-based devices through interfacial engineering.

The Shanghai Synchrotron Radiation Facility Phase-II Project is now under construction and it consists of 16 newly built advanced beamlines. The experiments carried out at these new beamlines tend to be characterized by high flux, multi-mode, ultra-fast frequency, in situ and dynamic loading. To meet these emerging experimental demands of SSRF Phase-II beamlines, the authors have developed a unified and extensible data acquisition system based on Bluesky suite. It has been applied at the BL07U Spatial-resolved and Spin-resolved ARPES and magnetism beamline. The experiment results show that with up to 5 channel signals, the system is capable of collecting total electron yield signals of experimental sample and standard sample, and incident photon flux signals simultaneously. It improves the user experimental efficiency and quality. In addition, thanks to Bluesky suite, all devices can be abstracted as motors or detectors and then represented by a Python object. Therefore, with the architecture, modules and interface developed for BL07U, the system can be extended to more beamlines efficiently and easily.