Design of HARTREE: A Soft X-ray Beamline Dedicated to Dichroism Measurements at Hefei Advanced Light Facility

Abstract

The HARTREE beamline is a newly developed soft X-ray facility at the Hefei Advanced Light Facility, designed to address the growing demand for element-specific characterization of spin, orbital, and lattice degrees of freedom in quantum materials. Covering an energy range of 250–2000 eV, the beamline targets the L-edges of 3d and 4d transition metals, M-edges of rare earths, and K-edges of light elements (C, N, O). The optical layout features a dual-EPU43.5 source operating in either collinear (high-flux) or parallel (dual-beams) modes, coupled with a variable-line-spacing plane grating monochromator (VLS-PGM) and Kirkpatrick-Baez (KB) focusing mirrors, delivering a resolving power of E/ΔE > 12,000 and a photon flux exceeding 1012 phs/s. To probe magnetic phenomena across temporal and spatial scales, HARTREE integrates three specialized end-stations: (1) A Superconducting Magnet end-station (SCM-XMCD) providing extreme environments (9 T, 2 K) and a high-speed polarization switch using chopper systems (1000 Hz) for high-sensitivity spectroscopy of weak magnetic signals; (2) A Vector Magnet station (VM-XMCD) equipped with a 4-dimensional sample environment (comprising three-dimensional translation along x, y, and z axes and Rz rotation about the vertical axis) and a 3 × 3 μm2 micro-focus, enabling time-resolved X-ray Ferromagnetic Resonance (XFMR) up to 8 GHz for ultrafast spin current mapping; and (3) A Photoemission Electron Microscope (PEEM) with a liquid helium stage (<20 K) and 20 nm spatial resolution for real-space imaging of nanoscale magnetic domains. Furthermore, the implementation of on-the-fly energy scanning reduces acquisition times while maintaining spectral fidelity. By synergizing these capabilities, the HARTREE beamline establishes a comprehensive platform for advancing spintronic devices, antiferromagnetic memory, and single-molecule magnets.