  A large body of knowledge about magnetism is attained from models of
interacting spins, which usually reside on magnetic ions. Proposals beyond the
ionic picture are uncommon and seldom verified by direct observations in
conjunction with microscopic theory. Here, using inelastic neutron scattering
to study the itinerant near-ferromagnet MnSi, we find that the system's
fundamental magnetic units are interconnected, extended molecular orbitals
consisting of three Mn atoms each, rather than individual Mn atoms. This result
is further corroborated by magnetic Wannier orbitals obtained by ab initio
calculations. It contrasts the ionic picture with a concrete example, and
presents a novel regime of the spin waves where the wavelength is comparable to
the spatial extent of the molecular orbitals. Our discovery brings important
insights into not only the magnetism of MnSi, but also a broad range of
magnetic quantum materials where structural symmetry, electron itinerancy and
correlations act in concert.
