Itinerant electron magnetism in 3d-transition metals (invited)

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Abstract
Inelastic neutron scattering experiments performed on the 3-d transition metal ferromagnets have revealed striking behavior associated with the magnetic excitations found in these materials. Of particular importance is the disappearance of the spin-wave mode above a certain cut-off wave vector and the existence of spin-waves well above the Curie temperature. These phenomena are inconsistent with predictions of localized spin models but can be understood if the ’’magnetic electrons’’ are assumed to be itinerant. At low temperatures, quantitative predictions of the itinerant electron theory based on KKR energy band calculations have been found to be in excellent agreement with experiment. In addition, these calculations predicted the existence of an optical spin-wave mode in nickel which was recently observed. The extrapolation of the low temperature theory to finite temperatures, based on the concept of a temperature dependent spin splitting of the electron bands, appears to be inconsistent with experiment. More realistic attempts to develop a finite temperature theory are currently under investigation.