Non-quasiparticle effects in half-metallic ferromagnets

Abstract

The unusual electronic structure of the half-metallic ferromagnets (HMF) is analysedtaking account of correlation effects (electron–magnon interaction, in particularspin-polaron effects). Special attention is paid to the so-called non-quasiparticle(NQP) (incoherent) states which arise in the minority- (majority-) spin gapabove (below) the Fermi level and which may make considerable contributionsto the electronic properties. First-principles calculations of the NQP states inHMF within the local-density approximation plus dynamical mean field theory(LDA+DMFT) are reviewed. These states can be probed, in particular, by spin-polarized scanningtunnelling microscopy. They also lead to observable effects in core–hole spectroscopy,nuclear magnetic relaxation and contribute to the temperature dependence of impurityresistivity, etc. The peculiarities of the transport properties of three- and two-dimensionalHMF are discussed, which are connected with the absence of one-magnon spin-flipscattering processes.