Magnetic-field-induced biaxiality in an antiferroelectric liquid crystal

The magnetic-field-induced biaxiality of the originally uniaxial antiferroelectric chiral smectic (Sm-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$) phase of 4-(1-methyl-heptyloxycarbonylphenyl) 4’-octylbiphenyl-4-carboxylate (MHPOBC) has been studied in a magnetic field applied perpendicular to the helical axis. The observed distortions of the central part of the conoscopic figures are explained on the basis of a perturbative approach to light propagation in spatially modulated birefringent phases. The critical magnetic field for the unwinding of the helical structure of the Sm-${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ phase of MHPOBC is 13 T at 89 °C and is strongly temperature dependent.