Ferromagnetic 3d-metals: On the definition of “local bands”

The basic concept of a picture for itinerant ferromagnetism is discussed. The central point is that a local exchange splitting and local moments, exist even above the transition temperature T_c. Transverse fluctuations (and not magnitude fluctuations, as in Stoner theory) are the dominant source for the phase transition to the paramagnetic state. The author's Green's function method is extended to the use of a full bandstructure including hybridization and general electron-electron interactions. Spin waves are also discussed.