Biological materials: Fishing for compliance.

692 nature materials | VOL 7 | SEPTEMBER 2008 | www.nature.com/naturematerials constructed chiral anionic layers based on the bridged metal centres. The synthesis involves a subtle enantioselective interaction between a solution of enantiopure cations and a racemic mixture (equal amounts of the two enantiomers) of the metallic components. The reaction leads to the formation of the desired enantiopure chiral ferromagnetic layers within single crystals, with the absolute configurations of the metal centres controlled by the chirality of the enantiopure organic cations. These chiral crystals did indeed show the hoped-for large magneto–chiral dichroism in the ferromagnetic phase, with equal and opposite signals for the two enantiomeric forms. In the paramagnetic phase a weak dichroism is observed, which increases rapidly through the paramagnetic-to-ferromagnetic transition at the Curie temperature of 7 K, increasing by a factor of 17 between 11 K and 3 K, and closely following the thermal variation of the magnetization3. This research has demonstrated the importance of ferromagnetism for generating large magneto–chiral effects. Owing to the bistability inherent in a magnetically ordered state, ferromagnetic chiral media could be exploited for data storage with detection based on magneto– chiral dichroism rather than magnetic circular dichroism (the Faraday effect in absorption). If they are also conductors, large values of magneto–chiral anisotropy in conduction1 can be expected in chiral ferromagnetic materials, which could be relevant to, amongst other things, magneto–resistive sensors. The work by Train and colleagues provides a paradigm for how close interactions between chemists and physicists can lead to new rationally designed multifunctional materials, and opens the door to a whole new realm of phenomena and applications supported by magneto–chiral materials.