Abstract
An alternative model for the origin of spin density waves in chromium is presented in terms of a mixture of two electronic structures, one a normal anti-ferromagnetic and the other non-magnetic. The Invar effect in chromium and chromium-rich alloys and the rapid change in electronic structure with Mn, Re and V additions follows from this model. In α-Mn there exists essentially three crystallo-graphic sites each with a different atomic volume and magnetic moment. The Invar effect and the pressure dependence of the Néel temperature follows from this model.