Reorientation of ferroelectric nematic liquid crystals under out-of-plane electric and magnetic fields

• Electric fields reorient ferroelectric nematic liquid crystals with no threshold. • Continuum theory with simulations and experiments show the phenomenon. • The effects of both electric and magnetic fields are discussed. • Comparison with the nematic Fredericks transition is highlighted. The recently discovered ferroelectric nematic liquid crystals combine fluidic properties and spontaneous electric polarization with an externally controllable molecular arrangement. The huge spontaneous polarization and large apparent permittivity along with the soft nature suggest an extreme sensitivity and reconfigurability by external electric fields, promising new perspectives in applications. In this paper, we show that it is possible to induce a thresholdless reorientation of the molecular arrangement by an electric field normal to the initial orientation and the bounding surfaces. Continuum theoretical description involving orientational elasticity, ferro-electrostatics, and an external electric field is presented, where the effect of magnetic fields applied in different directions is also discussed. Our simulations and experiments show thresholdless reorientation in contrast to the Fredericks transition observed in conventional nematic liquid crystals, while the ordering remains to be monodomain except at the boundaries. The experiments also show the importance of ionic charges present in the material.