18 January 2007
Prussian Blue Wrangled Into Data Storage Duty
by Kate Melville 
Prussian Blue, a pigment used in paints, could form the basis of new high efficiency data storage devices. French scientists have created a compound from Prussian blue that can act as a magnetic medium where each bit of binary data is stored on a molecule. Prussian Blue is not magnetic at the outset, but it can become magnetized by the effect of light and return to its initial state by heating. Researchers at the Institute of Molecular Chemistry and Materials of Orsay (CNRS/University of Paris XI) and the Laboratory of Inorganic Chemistry and Molecular Materials (CNRS/University of Paris VI) showed that this change of state is due to the collective modification of the position of the atoms, induced by light. Their work was presented in the journal Angewandte Chemie.
By replacing some of the atoms of iron with cobalt, they managed to transform the pigment into a compound that can act as a magnetic switch. Illuminated by a red light at low temperature (-150°C), the compound shifts from a non-magnetic state to a magnetic state in a way that is stable over time. If it is heated, it returns to the non-magnetic state. The change of state is due to the transfer of an electron from the cobalt to the iron (and vice-versa), by absorption of light or thermal energy. Using a synchrotron, the scientists observed a collective modification of the position of the atoms induced by the shift of the electron from one atom to the other. When the electron goes from the iron atom to the cobalt atom due to the red light, the three-dimensional links between the cobalt, nitrogen, carbon and iron atoms, which were initially bent, become linear. This structural modification is responsible for the existence of this magnetic state and its stability over time. The new compound can perfectly reproduce the storage function of traditional components, say the researchers, who believe the material could be widely used in future miniaturized information storage devices. Source: Laboratory of Inorganic Chemistry and Molecular Materials (CNRS/University of Paris VI)
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