Introduction

Abstract

Most research into the magnetic properties of crystalline solids in the last forty years has been focused on the iron-group transition metals, the rare earth metals (such as gadolinium), and the vast number of compounds of these metals with other elements. It is for the most part only in the last fifteen years that the third group of magnetic elements, the actinides, have come under experimental and theoretical investigation (see Table 1). The actinides are elements with atomic number greater than 89, of which U, Np, and Pu are the best-known examples. They have many radioactive isotopes requiring special care in handling. The compounds of actinide elements include metals, semiconductors, and insulators and fall into the eight broad classes listed in Table 2. These materials are usually either ferromagnetically or antiferromagnetically ordered at low temperatures.