Magnetically induced Freedericksz transition and relaxation phenomena in nematic liquid crystals doped with azo-dyes

A static and dynamic investigation was performed on liquid crystal cells containing pure nematics and nematics doped with an azo-dye (Methyl Orange). It was found that the critical field for magnetic Freedericksz transition was decreased in samples containing the “trans” isomer and increased in those containing the “cis  ” isomer. Changes in the relaxation time _τA${\tau }_A$, _τB${\tau }_B$ intervening when switching on/off the magnetic field were also noticed. A theoretical model was elaborated to explain these phenomena.