Evidence for classical critical behavior at the nematic-isotropic phase transition

Magnetically induced birefringence measurements were performed in the isotropic phase of methoxybenzylidene butylaniline (MBBA). Over the entire temperature range studied, $\Delta n$ was found to be linear in $H^2$ to fields over 10 T. This result is consistent with the Landau model of the nematic-isotropic transition, and strongly inconsistent with the results of Keyes and Shane [Phys. Rev. Lett. 42, 722 (1979)] in a similar experiment. Their results indicate both the approach of a field-induced critical point and tricritical behavior near the phase transition.