Local Magnetic Moments and the Mossbauer Effect

Abstract

In this brief paper we will describe the use of the Mossbauer effect to study the behavior of the magnetic properties of impurities in metals. This problem has been named the “localized moment problem” and in recent years has been studied quite thoroughly both theoretically and experimentally.¹ At the beginning of the last decade, it was believed that significant theoretical and experimental progress had been made. Based on earlier concepts of Friedel,² both Anderson³ and Wolff⁴ presented a sound theoretical model for studying the magnetic behavior of a single impurity in a host metal. At about the same time systematic studies of low concentration impurities in alloys of the 4d transition metals had revealed rules for the occurrence and definition of a magnetic impurity.⁵ At this point in the study of the localized moment problem most researchers felt that significant progress had been made and ultimately a first principle understanding of the occurrence of elemental magnetism would soon be presented. This optimism was based on the historical belief that after solving the single impurity problem one could go on to the two impurity problem and then the many impurity problem. Ultimately it was felt that a magnetic metal like Fe could be considered as consisting of magnetic impurities at each lattice site. Unfortunately even the single impurity problem has turned out to be more difficult than first realized and a multitude of magnetic behaviors has been associated within even the single impurity limit depending upon the nature of both the impurity and the host.

Also Physics Department, Massachusetts Institute of Technology.

Supported by the U.S. Air Force Office of Scientific Research.