Material gains

-- (Credit: Illustrations: Vishwajyoti)MOLECULAR magnetism, which involves designing and synthesising molecules that have properties like long-range magnetic ordering, is one of the most fascinating fields of research in material science. Many materials with this pro~ perty, useful in items like magnetic memory devices, !)ave been synthesised. But all of them suffer from the same problem -they are magnetic only at a very low temperature, losing their remarkable qualities at room temperature.

Now, M Verdaguer and his co- workers at Laboratoire de Chimie des Metaux de Transition, Paris, France, have reported the synthesisofa new compound which retains its magnetic property at ambient temperatures. Tl:le material belongs to the Prussiap blue family of compounds. Prussian blue can bethought of as an archetype of mixed valence compounds, with two identical metals in different oxidation states.

A compound having similar proper- ties had been synthesised five years ago. This compouQd -derived from varia- dium and tetracyat;loethylene -is, however, amorphous and fragile; conse- quently, studying its molecular proper- ties is difficult. But the new material has been synthesised by combining hexacyanometalate with a Lewis acid (a chemical compound that can accept a pair of eJectrons).

If the elements involved in the inter- action are transition metal ions, then the r~sulting inte!action can be described by well understood principles. This is what makes the discovery excit- ing, because with an underlying theory, it should be possible in principle to tune the compound's magnetic properties. The transition temperature -the tern - perature above which the materialloss its magnetic ordering -is 42C in the case of the new compound. Though there are not many applications of the compound at present, in the near future one might see its use in memory devices or temperature s~nsitive magnetic switches.