Thermal convection in a planar nematic liquid crystal with a stabilizing magnetic field

We report experimental results for thermal convection in a horizontal layer of a planar nematic liquid crystal [4-n-pentyl-4’-cyanobiphenyl (5CB)] heated from below in a uniform horizontal magnetic field H. The threshold for convection and the critical wave-vector components were measured as a function of H. The convection rolls were oriented with their axes normal (oblique) to the field direction for H<${\mathit{H}}_{\mathit{L}1}$ (${\mathit{H}}_{\mathit{L}1}$<H<${\mathit{H}}_{\mathit{L}2}$), where ${\mathit{H}}_{\mathit{L}1}$ and ${\mathit{H}}_{\mathit{L}2}$ are the lower and upper Lifshitz fields, respectively. Above ${\mathit{H}}_{\mathit{L}2}$ the orientation was parallel to H. The dependence of the orientation on H near ${\mathit{H}}_{\mathit{L}1}$ and ${\mathit{H}}_{\mathit{L}2}$ agrees with theoretical predictions.