Singlet magnetism in intermetallic UGa₂ unveiled by inelastic x-ray scattering

Using high resolution tender x-ray resonant inelastic scattering and hard x-ray nonresonant inelastic scattering beyond the dipole limit we were able to detect electronic excitations in intermetallic UGa2 that are highly atomic in nature. Analysis of the spectral lineshape reveals that the local 5f(2) configuration characterizes the correlated nature of this ferromagnet. The orientation and directional dependence of the spectra indicate that the ground state is made of the Gamma(1) singlet and/or Gamma(6) doublet symmetry. With the ordered moment in the ab plane, we infer that the magnetism originates from the higher lying Gamma(6) doublet being mixed with the Gamma(1) singlet due to intersite exchange, qualifying UGa2 to be a true quantum magnet. The ability to observe atomic excitations is crucial to resolve the ongoing debate about the degree of localization versus itineracy in U intermetallics.