•A novel composite magnetite-polymer particle/lyotropic liquid crystal was obtained.•The experimental magnetic Fréedericksz transition using a laser beam was studied.•The estimated critical field was compared to our new theoretical model. We obtained a new highly ordered colloidal composite using specially manufactured magnetite-polymer nanoparticles and lyotropic liquid crystal. A good compatibility between the components was ensured by the functionalization of the particles during their synthesis. We studied the laser light transmission for the mixtures filled in sandwich-glass cells with homeotropic and planar treatment of the surfaces under external magnetic field. The Fréedericksz transition critical field was estimated, and its’ behavior was compared to our new theoretical model based on the Brochard-de Gennes one.