Conceptual Phase Diagrams and Their Applications to Itinerant Electron Magnetism

An adequate description of the magnetic properties of a solid requires not only a knowledge of the relative energies of the atomic outer-electron states, but also the location of a given electron state within a conceptual phase diagram of electronic properties. In the last few years the physical ideas essential to this task have been identified. My intent in this paper is to review briefly these ideas and to illustrate their usefulness. First, I develop the phase diagrams. Then I review briefly some complex magnetic and crystallographic properties exhibited by several metallic compounds and show how their magnetic order and the magnitudes of the observed atomic moments can be derived in terms of the phase diagrams, known variations across the Periodic Table, and qualitative arguments about the energy bands. These examples illustrate how, from a small set of physical ideas and the phase diagrams, it is possible to develop experimental strategies for controlled modification of known magnetic materials and for a search for new magnetic materials. Although development of fruitful experimental strategies is adequate justification for inclusion of a qualitative discussion in a theoretical conference, my hope is that a heightened confidence in the sufficiency of the physical ideas discussed will also aid the theorists’ search for simplified techniques with which to calculate the observed properties from first principles.