  In the present paper, we report a comparison study of SrFe$_2$As$_2$ and
SrFeAsF using M\"ossbauer spectroscopy. The temperature dependence of the
magnetic hyperfine field is fitted with a modified Bean-Rodbell model. The
results give much smaller magnetic moment and magneto-structural coupling
effect for SrFeAsF, which may be understood as due to different inter-layer
properties of the two compounds.
