SOFT FERROCHOLESTERIC IN A ROTATING MAGNETIC FIELD: PHASE DIAGRAMS

The dynamics of the helical orientation structure of a ferrocholesteric liquid crystal under the action of a rotating magnetic field at soft (finite) coupling between magnetic particles and a liquid crystal matrix is theoretically studied. The stationary regime of rotation of ferrocholesteric helix in the uniform magnetic field is analyzed. A system of integro-differential equations defining the orientation of liquid crystalline and magnetic subsystems and the critical parameters at the ferrocholesteric - ferronematic transition point with a finite coupling energy is obtained in the continuum theory. The orientation phase diagram of the ferrocholesteric - ferronematic transition at different values of the magnetic field strength and angular rotation velocity, coupling energy and magnetic field influence parameter is obtained for the stationary regime of rotation. It is shown that the critical threshold of the ferrocholesteric - ferronematic transition decreases as the coupling energy and the field influence parameter increase. The helix unwinding in the dipole mode is the most effective, as in the static case.