Presence of magnetic excitations in SmFeAsO

We measured dispersive spin excitations in $\mathrm{SmFeAsO}$, parent compound of $\mathrm{SmFeAsO_{\text{1-x}}F_{\text{x}}}$ one of the highest temperature superconductors of Fe pnictides (T$_{\text{C}}\approx$55~K). We determine the magnetic excitations to disperse with a bandwidth energy of ca 170 meV at (0.47, 0) and (0.34, 0.34), which merges into the elastic line approaching the $\Gamma$ point. Comparing our results with other parent Fe pnictides, we show the importance of structural parameters for the magnetic excitation spectrum, with small modifications of the tetrahedron angles and As height strongly affecting the magnetism.