  In comparison to 3d or 4f metals, magnetism in actinides remains poorly
understood due to experimental complications and the exotic behavior of the 5f
states. In particular, plutonium metal is most especially vexing. Over the last
five decades theories proposed the presence of either ordered or disordered
local moments at low temperatures. However, experiments such as magnetic
susceptibility, electrical resistivity, nuclear magnetic resonance, specific
heat, and elastic and inelastic neutron scattering show no evidence for ordered
or disordered magnetic moments in any of the six phases of plutonium. Beyond
plutonium, the magnetic structure of other actinides is an active area of
research given that temperature, pressure, and chemistry can quickly alter the
magnetic structure of the 5f states. For instance, curium metal has an
exceedingly large spin polarization that results in a total moment of about 8
Bohr magneton/atom, which influences the phase stability of the metal. Insight
in the actinide ground state can be obtained from core-level x-ray absorption
spectroscopy (XAS) and electron energy-loss spectroscopy (EELS). A sum rule
relates the branching ratio of the core-level spectra measured by XAS or EELS
to the expectation value of the angular part of the spin-orbit interaction.
