Effects of conduction electron excitation on x-ray magnetic circularly polarized emission in itinerant ferromagnets

We develop a theoretical method to calculate x-ray magnetic circularly polarized emission (XMCPE) spectra for itinerant ferromagnets, in particular, K α emission for transition metals. The effects of electron excitations in the d bands are treated by means of the Keldysh Green's function. In our theoretical framework, the ferromagnetic ground state and the excitations are described by a mean-field approximation and a single-bubble diagram, respectively. We apply our method to K α XMCPE spectra of metallic iron, and reproduce the observed tail structures on the low-energy side of each peak. Contributions from the excitations in the d bands depend strongly on the exchange interaction as well as the direct interaction between the 2 p and 3 d electrons. The dependence of the spectral intensity on emission angles with respect to the magnetization direction is cosinusoidal, indicating that K α XMCPE can be used to investigate the magnetization directions in bulk ferromagnets.