Le, M.D.: Magnetism and quadrupolar order in f-electron systems. , Thesis (Ph.D) University of London, 2009, 2009
Open Access Version
Abstract:
This thesis presents experimental results using bulk thermodynamic measurements and scattering techniques on compounds of f -electron elements in which the quadrupolar interaction is strong or dominant. In the case of PrB6, the exchange interaction between electric quadrupoles on neighbouring Pr sites drives a complex non-collinear magnetic order, whilst in UPd3 , the quadrupolar interaction is strong enough to suppress magnetic order and instead a series of quadrupolar ordered phases ensues at low temperatures. In addition to these two compounds, we also investigated the transuranium compounds NpPd3 and PuPd3 , and the solid solution system (Pu,Lu)Pd3 through work carried out at the Institute for Transuranium Elements of the European Commission. The experimental techniques used include x-ray resonant scattering, which is a direct probe of the f -electrons' multipolar properties, and inelastic neutron scattering which reveals the dynamics of the spins of the systems and can be an indirect probe of quadrupolar interactions. Furthermore, bulk measurements such as magnetic susceptibility, heat capacity and resistivity were used to elucidate the ground state properties of the f -electrons, away from the ordered phase. In particular, we present inelastic neutron scattering data on the ordered phase excitations of PrB6 , and the paramagnetic crystal field excitations of UPd3 and NpPd3; resonant x-ray scattering in the ordered phases of UPd3 ; and thermodynamic bulk properties measurements, including heat capacity and magnetic susceptibility, on the (Pu,Lu)Pd3 system which shows evidence of heavy fermion behaviour. Finally, this work also encompasses a program to calculate the single ion properties of actinide compounds using intermediate coupling theory, as it was found that the larger spin orbit and crystal field interactions in these systems cause a qualitative change in the magnetic susceptibility.