GRENOBLE, France -- A team of scientists has discovered a way to use a magnetic field to alter the transparency of a plastic disc. Bart van Tiggelen of the Universite Joseph Fourier and researchers from the Max Planck Institute made the discovery, which could lead to advances in optical switching devices. Last year, this same team discovered a photonic phenomenon similar to the Hall effect. The researchers observed the propagation of light through a plastic disc made partly of europium fluoride. The disc loses transparency when it is placed inside a magnetic field. The effect is similar to an electric phenomenon known as magnetoresistance -- so much so that the team is calling the discovery photonic magnetoresistance. "Our research effort is directed at light scattering in a magnetic field. We are doing fundamental research to see if there are other effects in this area," Because photons have neither charge nor mass and are not affected by magnetism, researchers attribute the effect to changes that the magnetic field makes on the atoms in the material. The research group discovered that the decrease in transparency is proportional to the square of the intensity of the magnetic field. Van Tiggelen compared the behavior of the photons in the heterogeneous europium fluoride to the walk of an intoxicated man. In homogeneous materials, the Faraday-rotated light walks in an orderly pattern. When the same light propagates in a heterogeneous material, it staggers, losing its intensity. According to van Tiggelen, the group chose europium fluoride because it exhibits a large Faraday rotation. The group also tested zinc sulfide and titanium dioxide. Zinc sulfide, he said, has a Faraday rotation in the opposite direction of europium fluoride. Van Tiggelen said that applications of this discovery are still far off. He added, however, that the discovery could lead to fiber optic switching mechanisms. He explained that if scientists can eventually exert control over photons that is similar to the control over electrons, optical systems may be designed to perform like electrical systems. The group has improved the effect so that transparency is reduced by 1 percent. Van Tiggelen said that the researchers are continuing to seek new materials that meet their criteria: a larger Faraday rotation and greater light scattering. "Our research effort is directed at light scattering in a magnetic field. We are doing fundamental research to see if there are other effects in this area," he said.