Dynamic Low-Spin—High-Spin Transition ofFe2+in1T−Fe

$1T\ensuremath{-}{\mathrm{Fe}}_{x}{\mathrm{Ta}}_{1\ensuremath{-}x}{\mathrm{S}}_{2}$ shows unusual behavior in the temperature dependence of the magnetic susceptibility and $^{57}\mathrm{Fe}$ M\"ossbauer isomer shift, as a result of a low spin ($^{1}A_{1\mathrm{g}}$) to high spin ($^{5}T_{2\mathrm{g}}$) transition of ${\mathrm{Fe}}^{2+}$. The fluctuation rate $^{1}A_{1\mathrm{g}}\ensuremath{\leftrightarrow}^{5}T_{2\mathrm{g}}$ is faster than ${10}^{7}$ ${\mathrm{sec}}^{\ensuremath{-}1}$.