Abstract
A homeotropically aligned nematic (MBBA) with negative dielectric anisotropy subjected to electric and magnetic fields has been investigated. If an electric field perpendicular to the nematic layer is applied, first the Fréedericksz transition takes place spontaneously breaking the rotational symmetry and subsequently the electrohydrodynamic instability (EHC) sets in. An additional magnetic field in the plane of the layer induces a preferred director orientation. The effects of the magnetic field on the EHC threshold voltage, on the critical wave vector and on the roll angle are examined as a function of the applied frequency. The data are compared with theoretical results. Furthermore, accompanying domain walls are characterized.