Half-metallic ferromagnets: From band structure to many-body effects

A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics (i.e., spin-dependent electronics). Classification of HMFs by the peculiarities of their electronic structure and chemical bonding is discussed. The effects of electron-magnon interaction in HMFs and their manifestations in magnetic, spectral, thermodynamic, and transport properties are considered. Special attention is paid to the appearance of nonquasiparticle states in the energy gap, which provide an instructive example of essentially many-body features in the electronic structure. State-of-the-art electronic calculations for correlated $d$-systems are discussed, and results for specific HMFs (Heusler alloys, zinc-blende structure compounds, ${\mathrm{CrO}}_{2}$, and ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) are reviewed.