Magnetic field induced orientational transitions in soft compensated ferronematics

In the framework of continuum theory, we study magnetic field induced orientational transitions in a ferronematic, i.e., colloidal suspension of magnetic nanoparticles in a nematic liquid crystal. We consider a compensated ferronematic which is not magnetized in the absence of a field. The effect of finite coupling energy between the liquid crystal and the particle surfaces, as well as the segregation effect on the orientational transitions in a ferronematic are studied. The possibility of existence of three regimes of ferronematic orientational behavior under applied magnetic field in the case of weak coupling between the dispersed phase and a liquid crystal is established. The induced magnetic field distortions of orientational structure are shown to have a threshold character. The analytical expressions for the threshold fields are obtained. The optical phase lag and intensity of light transmitted through the ferronematic layer as functions of applied magnetic field are studied.