The magnetic properties of a ferronematic, i.e., a nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (a few Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase).

Abstract. The influence of Cu 7 PS 6 nanoparticles with the average size 117 nm on the dielectric properties of planar oriented nematic liquid crystal 6CB has been investigated within the frequency range 10 1 …106 Hz and at the temperature 293 K. It has been shown that when changing the concentration of nanoparticles within the range 0 to 1 wt.%, the conductivity of the liquid crystal changes stronger than its dielectric permittivity. It has been shown that the electrical conductivity increases monotonously with increasing the concentration of nanoparticles. However, for this dependence a saturation effect is observed. The mechanism of this effect was proposed.

This work is devoted to the study of highly stable composite systems of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) doped with CoFeO magnetic nanoparticles. Ferronematic samples were prepared with two different weight concentrations: sample A 0.085 wt% and sample B 0.062 wt%. The interaction of CoFeO nanoparticles with the liquid crystal was investigated by small-angle X-ray-scattering and magnetization measurements. The obtained results reveal aggregates formed by magnetic nanoparticles that are oriented in the nematic phase. Moreover, the prepared samples show unexpected behaviour of a sudden change in magnetization, which is unusual for such ferronematics.