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

We report on the inelastic neutron scattering measurements aimed at investigating the origin of temperature-induced paramagnetism in narrow-gap semiconductor FeSb₂. We find that inelastic response for energies up to 60 meV and at temperatures ≈4.2, ≈300, 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 nonmagnetic S=0 singlet ground state to a state of magnetic multiplet in the localized-spin picture. Our data establish the quantitative limit of Seff2≲0.25 on the fluctuating local spin. However, a broad magnetic scattering continuum in the 15 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.