Magnetic and electric field induced periodic deformations in nematics

Abstract

This work reports theoretical studies on the occurence of a static periodic distortion (PD) in a nematic sample under the action of crossed electric (E) and magnetic (H) fields applied on a uniformly aligned initial director configuration (n $_{\rm o}$ ). Linear stability analysis with rigid anchoring hypothesis is employed. For homeotropic alignment of a nematic such as M1 which has negative dielectric anisotropy ( $\epsilon_{\rm A}<0$) and positive diamagnetic anisotropy ( $\chi_{\rm A}>0$), PD occurs when E and H are both in the sample plane. The direction of periodicity depends on the angle between E and H; PD is unfavorable when H is tilted sufficiently away from E. In a material (such as CCH-7) with $\epsilon_{\rm A}>0$ and $\chi_{\rm A}<0$, the direction of periodicity changes continuously in the H, E plane as a function of the strength and tilt of the stabilizing H relative to E. Possible effects of flexoelectricity, weak anchoring and director pretilt are discussed briefly.