The Magnetic-Field-Induced Birefringence of the Mixtures of the Chiral Molecules and the Ferronematic Liquid Crystals

The ferronemtaic state which was described theoretically by Brochard and de Gennes can be achieved by doping the liquid crystal with anisotropic ferromagnetic particles. The homeotropic liquid crystal film was successfully prepared for the ferronematic liquid crystal doped with low concentration chiral molecules. The magnetic-field-induced-birefringence due to molecular reorientation was treated both theoretically and experimentally. In the low field regime (<2.5G), it is theoretically predicted that the induced phase difference between the ordinary and extraordinary ray of a normally incident probe beam is proportional to the square of the external magnetic field and to the fifth power of the thickness of the sample film. This is verified by the experimental results. The effect of the chiral molecules appears in the effective elastic constant, ke , which will decrease and then increase with respect to the increasing of the concentration of the chiral molecules.