A SYSTEM FOR MAGNETIC CIRCULAR-DICHROISM MEASUREMENTS WITH A 10-M TOROIDAL GRATING MONOCHROMATOR

A system of remotely-controlled apertures have been installed in the Synchrotron Radiation Center 10-m toroidal grating monochromator (TGM) for production of circularly-polarized light. In addition to allowing normal operation of the beamline, the apertures can be adjusted to block any fraction of the incoming beam without excessive heating and outgassing. This selective blocking of the light produces an appreciable elliptical polarization of the incoming light. Over the energy range of the 10 m TGM high energy grating, from 200 to 800 eV, the beamline optics do not significantly affect the polarization. The 10-m instrumental energy range overlaps the binding energies of the L-shell core levels of the important transition-metal materials. Calculations have been performed to estimate the performance of the aperture system as a function of energy. The results indicate that for an aperture position transmitting 20% of the synchrotron flux, the degree of polarization should be about 85% and should be reasonably constant over the photon energy range. With the light masked, magnetic circular dichroism was observed by measuring total yield with different orientations of sample magnetization and photon spin. Thin films of magnetic materials on magnetic and non-magnetic substrates have been studied.