Field-induced magnetism in itinerant f-electron systems: U, Pu, and Ce.

We demonstrate, by means of first-principles calculations, that in the field-induced magnetic state of [alpha]-cerium and [alpha]-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 [alpha]-uranium in very good agreement with experiment. The calculated form factor of [alpha]-cerium, when assuming that the [ital f] electron is itinerant, is very different from the localized Ce[sup 3+] form factor, and we propose that a measurement of the magnetic form factor of [alpha]-Ce can indicate whether the [ital 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.