EFFECTS OF A MAGNETIC-FIELD ON THE NEMATIC-SMECTIC A TRANSITION IN LIQUID-CRYSTALS

The effects of magnetic field on the nematic-smectic A phase transition in liquid crystals are investigated within the framework of McMillan's molecular field theory. It is shown that the tricritical point (TCP) can appear on the nematic-smectic A phase boundary as the magnetic field increases. The phenomenological de Gennes formula under the magnetic field is also derived from the molecular field theory. It is also pointed out that an electric field of about 500 kV/cm can induce a TCP as well, which might be attainable experimentally under favorable conditions.