Semimetallic behavior in Fe₂VAl: NMR evidence

We report the results of a ²⁷Al and ⁵¹V nuclear magnetic resonance study of Fe₂VAl at temperatures between 4 and 550 K. This material has been a subject of current interest due to indications of possible heavy fermion behavior. The low-temperature NMR relaxation rate follows a Korringa law, indicating a small density of carriers at the Fermi level. At elevated temperatures, the shifts and relaxation rates go over to a thermally activated response, a semiconductorlike behavior, consistent with separate low-lying bands removed from the Fermi-level. These results are consistent with recent electronic structure calculations, and can explain both the reported activated resistivity as well as the Fermi cutoff exhibited in photoemission studies. While we observe nonstoichiometric samples of (Fe_1-xV_x)₃Al to be magnetic, the x=0.33 composition is nonmagnetic, with narrow NMR linewidths.