ABSTRACT
Many years ago, Matthias and co-workers, in a series of electron spin resonance (ESR) and nuclear magnetic resonance (NMR) experiments on nonmagnetic metals—metals with no permanent magnetic moment—observed surprising evidence for long-lived local spin packets in the ESR lineshape [M1960]. These data indicated the persistence of local magnetic moments. The magnetic moment was quickly traced to the presence of small amounts of magnetic impurities. While various systems, for example, Mn, Fe, and other iron group impurities in host materials, such as Cu, Ag, and Au, were studied, the common ingredient shared by all the impurity ions is that they possessed one or more vacant inner-shell orbitals. In addition, the experiments demonstrated that varying the kind and amount of the magnetic impurities did not always result in the formation of local magnetic moments in nonmagnetic metals. This finding added to the intrigue and established the question of the formation of local magnetic moments as central to understanding magnetism and transport in solids. In this chapter, we describe the origin of local moments, focusing primarily on Anderson's model [A1961], the model that rose to the fore as the standard microscopic view of local magnetic moment formation in metals.
