Absence of magnetic moments in plutonium

Abstract

Many theories published in the last decade propose that either ordered or disordered local moments are present in elemental plutonium at low temperatures. We present new experimental data and review previous experimental results. None of the experiments provide any evidence for ordered or disordered magnetic moments (either static or dynamic) in plutonium at low temperatures, in either the $\alpha$ or $\delta$ phases. The experiments presented and discussed are magnetic susceptibility, electrical resistivity, nuclear magnetic resonance, specific heat, and both elastic and inelastic neutron scattering. Many recent calculations correctly predict experimentally observed atomic volumes, including that of $\delta$-Pu. These calculations achieve observed densities by the localization of electrons, which then give rise to magnetic moments. However, localized magnetic moments have never been observed experimentally in Pu. A theory is needed that is in agreement with all the experimental observations. Two theories are discussed that might provide understanding of the ensemble of unusual properties of Pu, including the absence of experimental evidence for localized magnetic moments; an issue that has persisted for over 50 years.