Oct 8, 1999
Researchers have created an organic material that is magnetic at room temperature but does not contain iron. Previously organic materials were only magnetic near absolute zero and contained small amounts of iron. Now Wataru Fujita and Kunio Awaga from the University of Tokyo have discovered an organic compound that can switch from diamagnetism - a weak form of magnetism - to paramagnetism - a much stronger form - when its temperature is changed by a few degrees (Science 286 261). The research has implications for thermal sensors and storage media.
The material - 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) - is non-magnetic at very low temperatures. The paramagnetic effect is strong at room temperature, but as the compound is cooled, it becomes diamagnetic below 230 K. However, it is heated again, it does not become paramagnetic until the temperature reaches is 305K. This is an unusually wide hysteresis loop for a magnetic material.
Fujita and Awaga suggest that the reason for this unusual behaviour is a change in the crystalline structure of the compound. As the structure changes, so do the molecular orbits of unpaired electrons in the crystal. This change increases the electrostatic repulsion pressure on other unpaired electrons in the compound, leading to paramagnetism.