Beamline overview

X-ray Magnetic Circular Dichroism (XMCD) spectroscopy is used to determine element specific magnetic properties of materials as well as individual contributions of orbital and spin magnetic moments into total magnetic moment. The technique uses circularly polarized light of opposite helicity provided by the APPLE-II type helical undulator at XMCD beamline, BL-20. The beamline covers energy range from 300 -1000 eV for circular polarization and 300-2000 eV for plane polarization by using Varied Line Spacing Plane Gratings (VLS-PG) in Monk-Gillieson configuration. The monochromator can be operated in constant included angle mode as well as variable included angle mode. The monochromatized beam is focused by a toroidal mirror to a spot of ~ 400 µm (H) × 100 µm (V) at the sample. The experimental station of BL-20 is a UHV chamber with electromagnets placed outside. The typical pole gap inside the chamber is ~ 20 mm. There is a hole of ~ 13 mm diameter at the centre of pole of the electromagnets from where x-ray beam enters in the experimental station. It is equipped with a cryogen free cryostat to vary sample temperature in the range of 20 to 325 K.

Beamline parameters & Optical layout

The XMCD beamline (BL-20) uses circularly and plane polarized light emitted by an APPLE-II type helical undulator, U3.

1. First optical element is a vertically mounted toroidal mirror, TM1, which deflects the incoming beam horizontally at an angle of 3.5o (grazing angle of incident is 1.75o). It focuses the beam from the undulator vertically on to the entrance slit.
2. The monochromator of the beamline consists of a spherical mirror (SM), one long plane mirror (PM) and two VLS-Plane Gratings (900 lines/mm and 1800 lines/mm). The monochromator is designed in such a way that it can be used in both Variable Included Angle (VIA) mode and in Constant Included Angle (CIA) mode.
3. The post focusing optical elements are two horizontally mounted toroidal mirrors, M1, and M2, which focuses the beam on the samples into two experimental chambers. At present, we have only toroidal mirror (M1) and one experimental station (Expt-1). The other toroidal mirror (M2) and experimental station (Expt-2) are planned for future.

Experimental station

The experimental station of BL-20 is a UHV chamber with electromagnets placed outside. The typical pole gap inside the chamber is 20 mm. There a hole of ~ 13 mm diameter at the center of pole of the electromagnets from where the x-ray beam enters in the experimental station. It is equipped with a cryogen free cryostat to vary sample temperature in the range of 20 to 325 K.

Application Areas