Phase behavior and magneto-optic response of lyotropic liquid crystals with ferromagnetic nanoplates*

As a recently discovered soft mater system, ferromagnetic lyotropic liquid crystals offers great potential for various applications [Nature Communications, 7: 10394, 2016]. Here, we expand the potential applications of magnetic colloids by combining disk-shaped ferromagnetic nanoparticles with nonmagnetic nanosheets. We find that by doping with low concentration of ferromagnetic barium hexaferrite nanoplates, the magnetic susceptibility of suspensions of colloidal nanosheets, in this case exfoliated monolayer zirconium phosphate, is largely enhanced. Colloidal mixtures of these two kinds of disk-shaped nanoparticles form a series of stable mesophases, among which the paramagnetic nematic liquid crystal phase shows Hertz-scale magneto-optic response to applied fields. Polarized optical microscopy and synchrotron X-ray scattering are used to probe the ordering and dynamic response of this new colloidal system with and without applied magnetic fields.