Ferromagnetism and temperature-dependent electronic structure of hcp gadolinium

We use a combination of a many-body model analysis with an ``ab initio'' band-structure calculation to derive the temperature-dependent electronic quasiparticle structure of the rare-earth metal gadolinium. As a local-moment system Gd is properly represented by the ferromagnetic (multiband) Kondo-lattice model [$s\text{\ensuremath{-}}f(d\text{\ensuremath{-}}f)$ model]. The single-particle part of the model Hamiltonian is taken from an augmented spherical wave band calculation. The proposed method avoids the double counting of relevant interactions by exploiting an exact limiting case of the model and takes into account the correct symmetry of atomic orbitals. The weakly correlated $5d$ conduction bands become polarized via interband exchange coupling to the localized $4f$ levels with a distinct temperature dependence. This results in a Rudermann-Kittel-Kasuya-Yosida-type mechanism of coupling leading to the ferromagnetism of Gd. We get a self-consistently derived Curie temperature of $294.1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and a $T=0$ moment of $7.71{\ensuremath{\mu}}_{\mathrm{B}}$, surprisingly close to the experimental values. The striking temperature dependence of the $5d$ conduction bands provides insight into the origin of the temperature dependence of the photoemission data. The only parameter of the theory (interband exchange coupling $J$) is uniquely fixed by the band calculation.