Eur. Phys. J. B 8, 67-72 (1999)
Magnetic field induced instabilities of a doped lyotropic hexagonal phase
L. Ramos1, P. Fabre 2 , and L. Fruchter3
1 Laboratoire de Physique de la Matière Condenséeb, Collège de France, 11 place Marcelin Berthelot,
75231 Paris Cedex 05, France
2 UMR CNRS-Elf Atochem, 95 rue Danton, 92303 Levallois-Perret Cedex, France
3 Laboratoire de Physique des Solides, Bâtiment 510, Université Paris-Sud Orsay, 91405 Orsay Cedex, France
Received 10 February 1998
Abstract. A new anisotropic magnetic fluid is obtained using a colloidal suspension of magnetic particles of nanometric size (ferrofluid) as a component of a swollen lyotropic hexagonal phase. This doped hexagonal system exhibits specific behaviors when submitted to a magnetic field of weak intensity. The field-induced instabilities are described and interpreted; they result from a high anisotropy of the magnetic susceptibility of the medium, which is measured. It is finally shown that the magnetic properties of the doped hexagonal phase allows one a determination of the compression modulus of the system.
PACS. 75.50.Mm Magnetic liquids - 82.70.Dd Colloids - 61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order