THE INVAR PROBLEM

After briefly reviewing the history and practical applications of Invar, we present results of recent total energy calculations as a function of the magnetic moment and atomic volume E(M, V). Based on these results, we analyze Invar-relevant physical properties for a broad variety of fcc ferromagnetic and antiferromagnetic 3d-alloy systems as a function of the electron concentration. The observed systematics can principally be understood within the framework of the band calculations mentioned. We also give an answer to the question, why close to the Invar range martensitic fcc-bcc transitions occur. Finally we show that a deeper understanding of all the observed anomalies results from an analysis of available data as a function of the lattice constant. Almost quantitative agreement between experiment and theory allows the conclusion that the moment-volume instabilities are undoubtedly responsible for the magnetic, magnetovolume and structural properties exhibited by 3d-alloy systems.