Absence of localized-spin magnetism in the narrow-gap semiconductor FeSb2

We report inelastic neutron scattering measurements aimed at investigating the origin of the temperature-induced paramagnetism in the narrow-gap semiconductor FeSb2. We find that inelastic response for energies up to 60 meV and at temperatures 4.2 K, 300 K and 550 K is essentially consistent with the scattering by lattice phonon excitations. We observe no evidence for a well-defined magnetic peak corresponding to the excitation from the non-magnetic S = 0 singlet ground state to a state of magnetic multiplet in the localized spin picture. Our data establish the quantitative limit of S_{eff}^2 < 0.25 on the fluctuating local spin. However, a broad magnetic scattering continuum in the 15 meV to 35 meV energy range is not ruled out by our data. Our findings make description in terms of the localized Fe spins unlikely and suggest that paramagnetic susceptibility of itinerant electrons is at the origin of the temperature-induced magnetism in FeSb2.