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 42