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, τB intervening when switching on/off the magnetic field were also noticed. A theoretical model was elaborated to explain these phenomena.