Helicity-Modulation Technique Using Diffractive Phase Retarder for Measurements of X-ray Magnetic Circular Dichroism

Abstract

A diamond X-ray phase retarder has been combined with a phase-sensitive detection method to improve the accuracy of X-ray magnetic circular dichroism (XMCD) measurements. Fluctuation of the absorption coefficient of a magnetized sample was induced by photon-helicity switching at 40 Hz by flipping the phase retarder, and directly detected through a lock-in amplifier referring to the helicity-modulation frequency. This new technique for XMCD measurements 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.