29SiNMR and relaxation in FeSi

Abstract

${}^{29}\mathrm{Si}$ NMR spectra and spin-lattice relaxation measurements in FeSi at different magnetic fields ranging from 1.6 to 15 T, from 1.6 K up to 900 K, are reported. The spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$ and the Knight shift ${K}_{S}$ display very interesting temperature dependences, with three different regimes. At low temperatures $(T<~100\mathrm{K})$ ${T}_{1}^{\ensuremath{-}1}$ increases linearly on increasing temperature while ${K}_{S}$ is practically constant. In the intermediate temperature range $(100<~T<~350\mathrm{K})$ ${T}_{1}^{\ensuremath{-}1}$ shows a behavior typical of a gapped system, with an energy gap $\ensuremath{\Delta}\ensuremath{\simeq}560\mathrm{K}$ and tracking the homogeneous static susceptibility $\ensuremath{\chi}(T).$ For $T>~350\mathrm{K}$ the temperature dependence of ${T}_{1}^{\ensuremath{-}1}$ departs from that of the susceptibility. While $\ensuremath{\chi}(T)$ levels around 500 K, ${T}_{1}^{\ensuremath{-}1}$ continues to increase. From the experimental findings, insights on the spin dynamics of Fermi-like carriers with strong correlation are obtained.