Absence of localized-spin magnetic scattering in the narrow-gap semiconductor FeSb$_{2}$

We report inelastic neutron scattering measurements aimed at investigating the origin of the temperature-induced paramagnetism in the narrow-gap semiconductor FeSb$_2$. We find that inelastic response for energies up to 60 meV and at temperatures $\approx 4.2$ K, $\approx 300$ K and $\approx 550$ K is consistent with scattering by the lattice phonon excitations. Hence, we observe no evidence for a well-defined magnetic excitation corresponding to transitions between the non-magnetic ground state and states of magnetic multiplet in the localized spin picture. 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 magnetic states unlikely and suggest that paramagnetic susceptibility of itinerant electrons is at the origin of the temperature-induced magnetism in FeSb$_2$.