The temperature dependence of the ${\mathrm{Fe}}^{57}$ hfs in Fe${\mathrm{F}}_2$ has been obtained with the Mössbauer effect in the antiferromagnetic region. Data just below the Néel temperature yield a critical exponent $\beta =0.325\mathrm{}\pm 0.005$ and $D=1.36\mathrm{}\pm 0.03$. This value of $\beta$ differs slightly from that of 0.333±0.003 found in Mn${\mathrm{F}}_2$ by Heller. However, this latter value also provides an adequate fit to our data, but over a more restricted range of temperature. $D$ is larger than previously reported in other materials because of the larger magnetic anisotropy in Fe${\mathrm{F}}_2$. In the low-temperature region (0-50°K), the present measurements are in good agreement with the more precise determination of the temperature dependence of the ${\mathrm{F}}^{19}$ NMR by Jaccarino, indicating that both measurements reflect the sublattice magnetization.

• Received 17 April 1967

DOI:https://doi.org/10.1103/PhysRev.161.478