NMR probe of pseudogap characteristics in Fe_2+xV_1-xAl

We report the results of a ⁵¹V nuclear magnetic resonance (NMR) study of Fe_2+xV_1-xAl, near the ordered composition with x=0, at temperatures between 4 and 500 K. All compositions are found to be metallic or semimetallic, though electrical resistivity has indicated a metal-insulator transition at x=0. The low-temperature NMR relaxation rates for stoichiometric (x=0) and nonstoichiometric (x=0.10 and -0.05) compounds follow a Korringa law, associated with a finite density of carriers at the Fermi level. High-temperature relaxation rates for x<~0 go over to a semiconductorlike activated form, providing information about the gap structure near the Fermi energy. The results are consistent with pseudogap features identified by recent band-structure calculations, although with smaller energy splittings. We analyze pseudogap changes vs composition, and compare the band-filling behavior to a recent coherent potential approximation calculation.