Quantum Theory of Magnetism

Although it is one of the oldest physical phenomena studied, magnetism con- tinues to be an active and challenging subject. This is due to the fact that mag- netic phenomena represent a complex application of quantum mechanics, statistical physics, and electromagnetism. As new magnetic materials are syn- thesized and new experimental conditions realized, the very fundamentals of these subjects are expanded. Thus, the Kondo effect, like superconductivity, stimulated the development of many-body techniques; spin glasses with their competing interactions are leading to advances in statistical physics; and angle- and spin-resolved photoemission is probing details of transition-metal electronic states never before possible. I have not tried to incorporate all the new developments in this subject since the first edition ten years ago. My purpose is still the same - to use linear response theory to establish a common conceptual basis for understanding a variety of magnetic phenomena. Many recent developments fit into this frame- work and have been included.