NMR study of Al substitution effects in FeSi

We report the results of 27Al NMR Knight shift measurement on FeSi 1− x Al x ( x=0.02 and 0.05) as related to the influence of Al substitution on the magnetic properties and energy gap features of FeSi. For both compositions, the temperature-dependent 27Al NMR Knight shifts exhibit activation-type behavior with the broad maximum at around 400 K. The observed data can be well reproduced by using a model band structure with two narrow peaks in the density of states separated by a small energy gap. The deduced gap was found to be insensitive to the Al content, indicative of little modification on the band structure of FeSi with addition of itinerant carriers. However, the absolute value of Knight shift increases with Al concentration, revealing an enhancement of the Pauli-type spin susceptibility via Al substitution.