Within the continuum theory we study the magnetic segregation effects in ferronematics, i.e., suspensions of monodomain magnetic particles in nematic liquid crystals. Orientational and concentrational distributions in a ferronematic layer are obtained as functions of a magnetic field strength for different values of material parameters. Tricritical behavior of the Fréedericksz transition in ferronematics induced by magnetic field is revealed. It is found out that this transition can be either first- or second-order transition depending on the segregation degree. We derive the analytical expression for the tricritical segregation parameter, determining the phase-transition character change. The dependence of birefringence on the external magnetic field and the segregation parameter is studied.
A mean-field theory is developed describing in what way a small amount of ferromagnetic nanoparticles embedded in a nematic liquid-crystalline matrix affects the order parameters and the temperature of the nematic-isotropic phase transition. In such a suspension, often termed ferronematic, the ability of the particles to be aligned by the magnetic field results in occurrence of a partially oriented (paranematic) state above the transition temperature. This fact entails the possibility of field-tuning the transition temperature in both ways: up and down. The pertinent field-dependencies are obtained and analyzed. The same description applies to liquid-crystalline suspensions of ferroelectric nanoparticles tuned by the electric field.
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