Orbital and spin sum rules in x-ray magnetic circular dichroism

Abstract

X-ray magnetic circular dichroism (XMCD) in the ${\mathit{L}}_{2,3}$ absorption spectra of transition metals is a relatively new experimental technique for the investigation of magnetism. XMCD is element specific, giving it obvious advantages over methods which measure averaged magnetic properties. Another potential strength of XMCD is the separate quantitative measurement of 〈${\mathit{L}}_{\mathit{Z}}$〉 and 〈${\mathit{S}}_{\mathit{Z}}$〉 through application of dichroism sum rules. In this paper we present the results from a set of experiments designed to test the applicability of the dichroism sum rules to XMCD spectra measured by total electron yield. We find that with proper experimental control of angle of incidence, degree of polarization and film thickness, the total electron yield measurement of absorption spectra is accurate to within 5%. The uncertainties involved in applying the dichroism sum rules are discussed in detail, including possible effects of diffuse magnetic moments which are known to exist in Fe, Co, and Ni. The magnitude of these uncertainties makes it difficult to obtain absolute values of 〈${\mathit{L}}_{\mathit{Z}}$〉 and 〈${\mathit{S}}_{\mathit{Z}}$〉, however, the dichroism sum rules are shown to be qualitatively accurate and therefore capable of measuring changes in 〈${\mathit{L}}_{\mathit{Z}}$〉 and 〈${\mathit{S}}_{\mathit{Z}}$〉.