Phase diagram of ferroelectric liquid crystals in an external magnetic field

The phase diagram of the ferroelectric smectic liquid crystal DOBAMBC in an external magnetic field H is analysed and the transition temperatures between the disordered Sm A, helicoidal Sm C* and homogeneously ordered Sm C phase are determined as functions of H by laser light diffraction measurements. Sm C* - Sm C transition line shows close to the transition temperature an anomalous behaviour of a similar character as the pitch of the helix. Both anomalies can be qualitatively explained by a non-linear coupling between the transverse polarization of molecules and their tilt from the normal to smectic layers.