Higher-order collinear interaction and magnetic excitation in the 5f localized system U₃Pd₂₀Si₆

The magnetic structure and excitation in a localized 5f system U₃Pd₂₀Si₆ were studied by means of neutron scattering. Our neutron diffraction experiments on a single-domain sample uniquely determined a remarkable collinear structure due to higher-order exchange interaction. We discovered a new type of spin-flop transition with collinear coupling. The localized nature of uranium 5f electrons with a 5f² Γ₅ ground state was clearly demonstrated by the observed crystalline electric field excitation. We observed beautiful ferromagnetic and antiferromagnetic spin-wave excitation over a whole Brillouin zone. Surprisingly, however, a clear low-energy quasi-elastic component was also observed around the antiferromagnetic zone centre. This low-energy quasi-elastic response is concluded to be the excitation of the quasi-particles due to hybridization between 5f and conduction electrons. The observation of this localized and itinerant dual nature in magnetic excitation indicates the possibility of partial localization based on an itinerant and two localized 5f electrons proposed theoretically.