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 Fréedericksz geometry using electrodes with circular cross sections. In the absence of a stabilizing magnetic (B) field, the voltage threshold (Vth) 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 Vth/2. The threshold voltage increases with B=‖B‖ 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.