ELECTROCONVECTION IN A HOMEOTROPIC NEMATIC UNDER THE INFLUENCE OF A MAGNETIC-FIELD

A homeotropically aligned nematic (MBBA) with negative dielectric anis otropy subjected to electric and magnetic fields has been investigated . If an electric field perpendicular to the nematic layer is applied, first the Freedericksz transition takes place spontaneously breaking t he rotational symmetry and subsequently the electrohydrodynamic instab ility (EHC) sets in. An additional magnetic field in the plane of the layer induces a preferred director orientation. The effects of the mag netic field on the EHC threshold voltage, on the critical wave vector and on the roll angle are examined as a function of the applied freque ncy. The data are compared with theoretical results. Furthermore, acco mpanying domain walls are characterized.