Helicity-modulation technique using diffractive phase retarder for measurements of X-ray magnetic circular dichroism

A diamond X-ray phase retarder has been combined with a phase-sensitive det ection method to improve the accuracy of X-ray magnetic circular dichroism (XMCD) measurements. Fluctuation of the absorption coefficient of a magneti zed sample was induced by photon-helicity switching at 40 Hz by flipping th e phase retarder, and directly detected through a lock-in amplifier referri ng to the helicity-modulation frequency. This new technique for XMCD measur ements was applied to the Fe K-edge in pure Fe foil. XMCD spectra of higher signal-to-noise ratio were obtained in shorter measuring time.