Reciprocal-space structure of neutron scattering from Stoner excitations in MnSi

When neutron scattering is used to probe magnetic excitations in solids, information about electrons' density distribution and interactions is encoded in the energy spectrum, as well as in the reciprocal-space structure of the scattering cross-section. In the local-moment limit that best describes magnetic insulators, the latter quantity translates into the atomic magnetic form factor and the dynamic structure factor of spin waves, which may vary significantly across Brillouin zones (BZs). In the itinerant limit that best describes magnetic metals, however, magnetic excitations consist of both spin waves and Stoner excitations; while the latter directly arise from electronic bands, it remains hitherto unknown how to relate their neutron-scattering cross-section, in particular the variations across BZs, to the electronic band structure and the associated wave functions. Here we present a systematic inelastic neutron scattering study of the prototypical itinerant magnet MnSi, along with first-principles and model-calculational analyses. Our result sheds new light on the local-itinerant dichotomy of magnetism in crystalline solids, by highlighting the notion of magnetic molecular orbitals for describing MnSi.