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Soft Matter and Biological Physics

Eur. Phys. J. E 1, 227-235

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

D. Spoliansky1,2 - V. Ponsinet1 - J. Ferré2 - J.-P. Jamet2

1 Laboratoire de Physique de la Matière Condensée, Collège de France, 11 place M. Berthelot, 75231 Paris Cedex 05, France
2 Laboratoire de Physique des Solides, Université Paris-Sud, Bâtiment 510, 91405 Orsay Cedex, France
vponsine@us.rhodia.com

Received 31 December 1998 and Received in final form 22 September 1999

Abstract
Ferrosmectics and ferrohexagonals are magnetic liquid crystals which consist of a lamellar and a hexagonal phase in which magnetic nanoparticles are incorporated. The magnetic field variation and the relaxation of the linear optical birefringence of ferrosmectics and ferrohexagonals and its time relaxation are measured in different geometries and compared with that of a ferrofluid sample. We interpret our data by the existence of a mean orientation of the magnetic particles in the lyotropic structure, which appears to be non-random in zero field. We conclude that the magnetic moments of the particles are preferentially aligned in the plane of the ferrosmectic layers and along the axis of the ferrohexagonal cylinders, respectively. To account for this preferred alignment, we propose that some of the particles in the ferrosmectic are adsorbed on the surfactant layers with their moment aligned in the lamellar plane, while the orientation of the moments in the ferrohexagonal is restricted to a cone around the cylinder axis.

PACS
75.50.Mm Magnetic liquids - 78.20.Ls Magnetooptical effects - 61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

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