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

Abstract 29 Si NMR measurements in FeSi up to 900 K are reported. For T ⩽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 χ ( T ). In the high temperature range an unexpected effect is observed with χ ( T ) and K S leveling around 500 K and then decreasing, while T 1 −1 continues to increase up to 900 K. Insights on the spin dynamics of Fermi-like carriers in strong correlation are derived.