Field-induced magnetism in itinerantf-electron systems: U, Pu, and Ce

We demonstrate, by means of first-principles calculations, that in the field-induced magnetic state of {α}-cerium and {α}-uranium the spin and orbital moments are coupled parallel rather than antiparallel as expected from Hund's third rule. This behavior gives a magnetic form factor for {α}-uranium in very good agreement with experiment. The calculated form factor of {α}-cerium, when assuming that the f electron is itinerant, is very different from the localized Ce³⁺ form factor, and we propose that a measurement of the magnetic form factor of {α}-Ce can indicate whether the f state is localized or itinerant. The field-induced magnetism of plutonium is shown to be almost exclusively of orbital character and the induced spin density of plutonium is highly anomalous.