The use of organized organic assemblies to direct the formation of mesoscopic inorganic structures presents many possibilities in the development of new functional materials. We have designed nano-films containing iron oxide particles, which exhibit magnetic properties at room temperature, and azobenzene by use of an alternate adsorption technique. Photoisomerization of the film was accompanied by a geometrically confined structural change, as reflected by changes in the electrostatic field. As a result, we were able to control the magnetic properties of this film by photoillumination at room temperature.