A 27 l NMR study of the mixed valence compound CeFe2 Al10

We report the results of a A 27 l nuclear magnetic resonance (NMR) study on the mixed valence compound CeFe2 Al10 at temperatures between 4 and 300 K. This material has been of current interest due to indications of Kondo insulator behavior. Five A 27 l NMR resonance lines that are associated with five nonequivalent crystallographic aluminum sites have been resolved. For each individual aluminum site, the temperature-dependent NMR Knight shift exhibits a character of valence fluctuation behavior with a broad maximum at around 70 K. At low temperatures, the Knight-shift results show a thermally activated feature, indicating the formation of an energy gap in this material. We interpret the Knight-shift data based on a proposed model density of states and the gap size of 110 K is properly estimated. A further analysis indicates that the observed gap in CeFe2 Al10 should be characterized as a pseudogap with a finite number of carriers at the Fermi level.