Theory of Fe and Mn 2p X-ray absorption for RbMn[Fe(CN) ₆]

We calculate the Fe 2p X-ray absorption spectrum (XAS) of RbMn[Fe(CN) ₆] in the ferromagnetic (FM) and photo-induced (PI) phases based on the calculation for the low-temperature (LT) and high-temperature (HT) phases. We use a configuration-interaction full-multiplet theory for a Fe(CN) ₆ cluster model and take account of the influence of adjacent Mn spins on the Fe(CN) ₆ cluster as an exchange field acting on the N 2p level. We predict that the Fe component of the magnetic moment can be decided by the Fe 2p XAS in the FM phase. In the PI phase, we predict a remarkable incident photon polarization dependence of the Fe 2p XAS. We examine the effect of a uniaxial crystal field on the Fe 2p XAS because RbMn[Fe(CN) ₆] in the LT phase takes the tetragonal structure which is one of factors for the temperature-induced valence transition. We also calculate the Mn 2p XAS of RbMn[Fe(CN) ₆] in the HT phase using a Mn(CN) ₆ cluster model. The average Mn 3d electron count is somewhat larger than the formal Mn valence (Mn ²⁺) because of ligand-to-metal charge transfer.