Controlling magnetism by means of electric fields and light is of great interest in view of practical applications in novel spin-dependent technologies. In this seminar I will present the successful modulation of the magnetic properties of light-sensitized magneto-electric and magnetic field-effect devices. The interaction with light is achieved through a GaMnAs /organic-dye hybrid structure while in field effect experiments a voltage is applied between ultra-thin films of FePt and a top gate electrode. Light exposure or electric field application in these devices generates changes in Curie temperature and coercive field that can be detected by magneto-transport measurements. A magnetic response to a controlled stimulus not involving a magnetic field is in both cases intimately related to the properties of the surface of the magnetic material.