Dynamical corrections to density-functional theory for quasiparticles in ferromagnetic4fsystems. II. Finite-temperature results for EuO

We present a theory for the temperature dependence of the electronic quasiparticle spectrum of ferromagnetic 4f systems. A concrete evaluation for the semiconductor EuO is performed and discussed. The study is based on a d-f exchange model, which has been exactly solved for T=0 in part I of this series. The exact solution allows us to fix the ‘‘free’’ Bloch energies ${\varepsilon }_m$(k) of the model in a highly realistic manner by application of a self-consistent spin-polarized band-structure calculation based on density-functional theory. For finite temperatures the d-f model is approximately solved by a many-body procedure, which takes special care for a proper treatment of spin-exchange processes between localized 4f moments and itinerant conduction electrons. The method reproduces the exact T=0 limiting case. The resulting f-spin correlation functions are calculated by a moment method. We discuss in detail the one-electron spectral density for k vectors along the ΓL direction, real and imaginary parts of the electronic self-energy, and quasiparticle densities of states. The prominent peaks of the spectral density are used to construct a temperature-dependent quasiparticle band structure. The temperature dependence is to first order due to the magnetization, and to second order due to a transverse correlation function of the localized 4f spins.