Magnetic, chemical and structural ordering in transition metals

Abstract

The metals in the middle of the transition metal series have a tendency towards antiferromagnetism, ordered AB alloy structures and lattice distortions based on a twofold superlattice. By contrast, at the beginning and end of the series the corresponding tendency is towards ferromagnetism, chemical segregation rather than alloy formation, and stable simple structures. The authors show how all these results can be understood in a unified way in terms of a general theorem published earlier. The argument applies quite generally to any set of tight-binding bands such as the d bands, independent of the specific structure. In a general sense the superlattice formation for approximately a half-filled band is like a Peierls transition, but it results from the electronic structure as a whole with no special role attached to the Fermi surface. The case of threefold superlattices is also discussed with examples.