Magnetic-field-induced Freedericksz transition of a nematic liquid crystaldoped with diazophenyl

The Freedericksz transition induced by a perpendicular static magnetic fiel d of a planar alignment nematic liquid crystal 4-amyl-4'-cyanodiphenyl(5CB) doped with trace 4[4'-(phenylazo)phenylazo]phenol (DAP) was studied. It wa s observed for the first time that the doped 5CB will dramatically decrease the magnetic field threshold compared to the pure 5CB while the convention al approach is doping with ferro-particles to decrease the magnetic field t hreshold. The results show that in this guest-host system, the guest DAP ha s much larger diamagnetic susceptibility anisotropy than pure 5CB and will force the 5CB molecule to reorientate under the lower magnetic field. (C) 2 001 Kluwer Academic Publishers.