Structure of the domain walls in soft ferrocholesterics

Using the continuum theory the influence of the external magnetic field on the ferrocholesteric-ferronematic phase transition is analyzed. The field b eing applied normal to the helix. Soft homeotropic coupling between the mag netic particles and the cholesteric molecules is assumed. The diamagnetic a nisotropy of the matrix is chosen to be positive. In this case the dipolar and quadrupolar mechanisms of orientational interaction with the external f ield compete with each other. The transition field as a function of the mat erial parameters of a ferrocholesteric is found. The reentrant ferrocholest eric and ferronematic phases are discussed. It is shown that rising the fie ld strength in the ferronematic phase leads to the change in the coupling b etween the particles and the director from homeotropic to planar one. A stu dy on the structure of the domain walls in ferronematic phase is undertaken .