Magnetic reorientation of nematic liquid crystals in non-Freedericksz geometries revisited

The director deformation inside a nematic cell, after a magnetic field is applied at an oblique angle α relatively to the initial homogeneous director, is studied considering a magnetic reorientation driven by hydrodynamic instabilities. This study is carried out for the splay and the bend non-Freedericksz geometries with α<π/2. Critical sample thicknesses are predicted for both the homogeneous deformed and the periodic director reorientations, giving way to a stripe pattern in the last case. The first transition, to homogeneous deformed director, is the equivalent of a second order phase transition, while the second transition, to a periodic director, is the equivalent of a first order phase transition.