Magneto-optical study of the orientation confinement of particles in ferrolyotropic systems

Ferrosmectics and ferrohexagonals are magnetic liquid crystals which consis t of a lamellar and a hexagonal phase in which magnetic nanoparticles are i ncorporated. The magnetic field variation and the relaxation of the linear optical birefringence of ferrosmectics and ferrohexagonals and its time rel axation are measured in different geometries and compared with that of a fe rrofluid sample. We interpret our data by the existence of a mean orientati on of the magnetic particles in the lyotropic structure, which appears to b e non-random in zero field. We conclude that the magnetic moments of the pa rticles are preferentially aligned in the plane of the ferrosmectic layers and along the axis of the ferrohexagonal cylinders, respectively. To accoun t for this preferred alignment, we propose that some of the particles in th e ferrosmectic are adsorbed on the surfactant layers with their moment alig ned in the lamellar plane, while the orientation of the moments in the ferr ohexagonal is restricted to a cone around the cylinder axis.