Ground state and electron-magnon interaction in an itinerant ferromagnet: half-metallic ferromagnets

Electron and spin Green functions of a Hubbard ferromagnet are calculated, both starting from the Stoner ground state and for a ferromagnet with Hubbard subbands. The temperature dependences of the spin-wave stiffness and damping, the magnetisation, the local moment on a site and the thermodynamic properties are investigated. The role of non-quasiparticle contributions, described by branch cuts of electron Green functions, is discussed. The non-quasiparticle ('ferrospinon') correction to the linear term in the specific heat is obtained. Experimental data on 'half-metallic' ferromagnets (in particular, spin polarisation and longitudinal nuclear relaxation rate) are analysed.