Molecular-statistical theory of ferromagnetic liquid crystal suspensions

A tensor variant of molecular-statistical theory is developed, within the framework of which it is possible to describe the appearance of spontaneous magnetization of anisotropic ferromagnetic nanoparticles dispersed in a nematic liquid crystal. Along with the tensor order parameters characterizing the orientational ordering of the liquid crystal and dispersed anisometric particles, the vector order parameter determining the magnetization of the ensemble of particles is additionally taken into account. A comparison between the previously known phenomenological theories of ferronematics and the proposed molecular-statistical theory is made. Phase diagrams of the suspension are constructed and the mean-field theory parameters are calculated on the basis of experimental data available in the literature.

Figure 1

Dependencies of the mean-field coupling parameters $\omega$ (red curves with filled circles) and ${\omega }_m$ (blue curves with open circles) on the polar order parameter $M$ for $\tilde{\kappa }=60$ (dotted curves) and $\tilde{\kappa }=130$ (solid curves).

Figure 2

Suspension phase diagrams in terms of reduced temperature and the mean-field coupling parameter ${\omega }_m$ for (a) $\omega =0$, (b) $\omega =0.4$, and (c) $\omega =1.2$. Solid lines correspond to the second-order phase transitions, and dashed lines correspond to the first-order phase transitions.