Magnetic studies of actinides: evidence for localized magnetism

The position of the 5f elements in the periodic table suggests that the electronic properties of these elements (and their compounds) will resemble those of the lanthanide series. However, the extended nature of the 5f wave functions leads to fundamental differences between 4f and 5f systems. Evidence for localized magnetism is reviewed. Results of magnetization, Moessbauer, neutron, and low-temperature x-ray experiments on Np, Pu, and Am compounds are used to illustrate both the similarities to and differences from lanthanide magnetism. A determination of the ground-state 5f electron wave functions is, in principle, possible by measuring the neutron magnetic cross section. The interpretation of such experiments on UO$sub 2$, USb, and PuP requires a knowledge of the radial extent of the 5f electrons, which is obtained from relativistic Dirac-Fock calculations, and the use of the tensor-operator formalism to treat the spin- orbit interaction. This interaction in Pu$sup 3+$ (a 5f$sup 5$ configuration) results in a magnetic form factor that initially increases with increasing scattering angle. For USb the experimental magnetic scattering is used to determine the ground-state wave function of the U$sup 3+$ ion. In addition the temperature dependence of the quadrupole moment in USb has been measured and yields information both on the size of the crystal-field and exchange interactions, and on the interplay between them. (auth