Half-metallic ferromagnetism:: Example of CrO2 (invited)

A broad classification scheme is proposed for half-metallic ferromagnets which embraces the possibilities of itinerant and localized electrons, as well as semimetallic and semiconducting electronic structure. Examples of each type are given. The problems of defining and measuring spin polarization are discussed and some characteristics of half-metals are reviewed with reference to chromium dioxide. (C) 2002 American Institute of Physics.