High-temperature correlated spin dynamics in FeSi from 29Si NMR relaxation

Si-29 NMR measurements in FeSi up to 900 K are reported. For T less than or equal to 350 K the spin-lattice relaxation rate T-1(-1) and the Knight shift K-S display behaviors typical of gapped systems and track the homogeneous static susceptibility chi(T). In the high temperature range an unexpected effect is observed with chi(T) and K-S leveling around 500 K and then decreasing, while Gamma(1)(-1) continues to increase up to 900 K. Insights on the spin dynamics of Fermi-like carriers in strong correlation are derived. (C) 2004 Elsevier B.V. All rights reserved.