Magneto-optical effects in nematic liquid crystal doped with Prussian Blue

The effects induced by the magnetic field into a mixture of a nematic liquid crystal with a small amount (0.5% by wt.) of ferromagnetic compound (Prussian Blue) were investigated. The optical effects were examined using Faraday configuration (i.e. magnetic field parallel to the incident light). We have measured the transmitted light intensity (He-Ne, square=632.8 nm) through the sample when subjecting it to an increasing magnetic field. We have also performed measurements on the liquid crystal mixture rotatory power, for different magnetic field values. We found that the ferromagnetic dopant induces optical activity into the nematic sample. When the mixture was subjected to an increasing magnetic field, the emerging light was found to be elliptically polarized, the ellipticity depending on magnetic field strength. The light transmission, the rotatory power and the ellipticity varied quasiperiodically at high magnetic field strengths. The observed phenomena may be explained if we consider that the rotatory polarization arises as a result of disturbing the nematic order by the ferromagnetic particles.