Bend periodic distortion of the texture in nematic lyotropic liquid crystals with and without ferrofluid

The creation of a bend periodic distortion by the action of magnetic fields (H) in a nematic lyotropic liquid crystal is discussed. The wavelength of this distortion ($P$), in the limit of small deformations, allows the measurement of $\frac{K_3}{{\chi }_a}$, where $K_3$ is the bend elastic constant and ${\chi }_a$ the anisotropy of magnetic susceptibility. In this limit, the dependence of $P^{-2\mathrm{}}$ with $H^2$ presents a linear behavior, predicted by the continuum elastic theory. The relation between $P$ and $H$ also allows us to determine an "effective field" in nematic samples doped with ferrofluid.