The collective ordering of magnetic nanoparticles in a nematic liquid crystal

An important goal for the development of novel nanomaterials based on magnetic nanoparticles dispersed in liquid crystals is the improvement of the sensitivity to magnetic fields. Despite the continuous research of the magnetically-controlled properties of such hybrid composite materials, known as ferronematics, a persistent challenge lies in achieving consistent homogeneity and colloidal stability of the nanoparticles in liquid crystal media. Therefore, the design of the magnetic nanoparticles needs to be compatible with the liquid crystal matrix. Coating nanoparticles with (pro)mesogenic ligands has been shown to be a versatile way of stabilizing magnetic nanoparticles in liquid crystal matrices. Here, we report about the effect of dendrimer-functionalized cobalt ferrite nanoparticles (CoFe2O4@dend) on structure and magnetic sensitivity in the thermotropic liquid crystal 4-pentyl-4 '-cyanobiphenyl (5CB) confirmed by small angle X-ray scattering (SAXS), magnetization and capacitance measurements. Our measurements reveal that for dendronized magnetic nanoparticles, the sensitivity to magnetic fields is improved. However, they exhibit a tendency to form clusters in the liquid crystal medium. These clusters induce a tilting of the overall ordering of the nematic director field due to magneto-nematic coupling.