Faraday Rotation near the Ferromagnetic Critical Temperature of CrBr3

We have used the Faraday effect to measure the magnetization of the insulating ferromagnet Cr${\mathrm{Br}}_3$ as a function of magnetic field (up to 9.5 kG) along 29 isotherms in the temperature range $T_c-{2.8}^{\circ }\mathrm{K}<T<\mathrm{}{T}_c+{6.7}^{\circ }$ K, where $T_c={32.884}^{\circ }$ K. The numerical results are presented in tabular form. We have also analyzed these data and found that the spontaneous magnetization goes to zero as ${(T_c-T)}^{\beta }$ with $\beta =0.368\mathrm{}\pm 0.005$. Along the critical isotherm $M\sim H^{\frac{1}{\delta }}$ with $\delta =4.28\mathrm{}\pm 0.1$ and the susceptibility for $M=0\mathrm{}$ and $T>\mathrm{}{T}_c$ diverges as ${(T-T_c)}^{-\gamma }$ with $\gamma =1.215\mathrm{}\pm 0.02$. All of the data are consistent with the hypothesis of the static scaling laws. Two simple parametric equations of state were tried, and the better of the two was found to represent the data quite well and be a useful form for calculations of thermodynamic properties in the critical region.