Molecular magnetism

Abstract

Most materials in magnetic applications are based on inorganic materials. Recently, however, organic and molecular materials have begun to show increasing promise. Purely organic ferromagnets, based upon nitronyl nitroxide radicals, show long range magnetic order at very low temperatures in the region of 1 K, while sulphur-based radicals show weak ferromagnetism at temperatures of up to 36 K. It is also possible to prepare molecule-based magnets in which transition-metal ions are used to provide the magnetic moment, but organic groups mediate the interactions. This strategy has produced magnetic materials with a large variety of structures, including chains, layered systems, and three-dimensional networks, some of which show ordering at room temperature and some of which have very high coercivity. Even if long range magnetic order is not achieved, interesting materials displaying the spin crossover effect may be prepared and these can have useful applications. Further magnetic materials may be obtained by constructing chargetransfer salts, which can produce metallic molecular magnets. A very exciting recent development is the preparation of single molecule magnets, which are small magnetic clusters. These materials can show macroscopic quantum tunnelling of the magnetization and may have uses as memory devices or in quantum computation applications. These systems can be powerfully studied using various experimental methods, including magnetometry, neutron scattering, muon-spin rotation and synchrotron radiation techniques. © 2006 Springer.