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 alpha 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 alpha 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 2p and 3d electrons. The dependence of the spectral intensity on emission angles with respect to the magnetization direction is cosinusoidal, indicating that Ka XMCPE can be used to investigate the magnetization directions in bulk ferromagnets.