We have studied the effects of perpendicular electric and magnetic fields on a liquid-crystal sample aligned between glass plates. One field is applied to stabilize the initial alignment, and the other is applied in order to drive the transition; the field and initial alignment directions define six possible geometries. We find that, in each case in which an electric field is present parallel to the glass plates, the Freedericksz transition from a uniform to an elastically deformed state can be first order irrespective of whether the electric field drives or stabilizes the transition. Using material parameters characteristic of the liquid-crystal 4-cyano-4’-n-pentylbiphenyl (5CB), we show that two of the transitions should be first order for this material in all values of stabilizing fields and that two should exhibit a tricritical point as the stabilizing field is increased.

• Received 17 May 1989

DOI:https://doi.org/10.1103/PhysRevA.40.6099