Effect of a stabilizing magnetic field on the electric-field-induced Fréedericksz transition in 4-n-pentyl-4-cyanobiphenyl.

Abstract

We report an experimental study on electric (E)-field-induced static and dynamic distortion of the nematic director in the bend Fr\'eedericksz geometry using electrodes with circular cross sections. In the absence of a stabilizing magnetic (B) field, the voltage threshold (${\mathit{V}}_{\mathrm{th}}$) for change from the initial homeotropic alignment is different when measured at different points of the sample and is nearly twice the bend threshold; the hysteresis width observed upon reduction of voltage is nearly ${\mathit{V}}_{\mathrm{th}}$/2. The threshold voltage increases with B=\ensuremath{\Vert}B\ensuremath{\Vert} but the static distortion above threshold is periodic with the wave vector in the sample plane being normal to the electrodes (Y stripes) at low B or parallel to the electrodes (X stripes) at high B. On continuous increase of voltage above the Y stripe threshold at constant B, the stripes initially become oblique (XY) and then disappear; subsequent diminution of voltage leads to exhibition of hysteresis with the formation of X stripes. At constant voltage above the Y stripe threshold, an increase of B leads to the appearance of X stripes. Rapid increase of voltage at constant B causes transient XY stripes. Some of the results are qualitatively discussed taking account of the nature of the E field.