Memory storage miniaturization is progressing steadily on to smaller and smaller devices. As structures go, one cannot miniaturize further than to the size of individual molecules. Precisely this has been achieved by a group of scientists from the INSTM units of the Universities of Florence and Modena, Italy, the ISTM-CNR, Florence, Italy, the Université Pierre et Marie Curie, Paris, France, and the Synchrotron Soleil, Gif sur Yvette, France [Mannini, et al., Nat. Mater. (2009), doi:10.1038/NMAT2374].

Although single-molecule magnets (SMMs) have been reported before (utilizing Manganese as magnetic material), the retention of magnetic hysteresis has been a problem as the Manganese ions gradually underwent reduction. The SMMs reported now consist of robust, propeller shaped organic molecules, comprising four high-spin Fe(III) ions, which display the redox stability missed in the Manganese compounds.

The molecules have been mounted on a gold surface, in order to make them individually accessible by scanning probes. “What we have shown is that the magnetic hysteresis of molecular origin is observable when the molecule is attached to a conductive surface,” says Roberta Sessoli, corresponding author. “We have selected gold as a surface material because our approach was a ‘wet’ one, i.e., using self assembly from a solution of magnetic molecules.” The result represents a breakthrough in nanomagnetism, since this compound excels in stability, magnetically as well as chemically, both in solution and crystalline form.

However, the question of writing and reading information from the individual molecules remains. “Scanning probe techniques are very promising, but also very expensive,” admits Sessoli. “Other methods might be employed, although very little is known at the moment about the transport properties of isolated molecules and their interplay with their magnetization state.” However, the scientists hope to learn more about the interactions of conducting electrons and magnetism at a fundamental level from these systems in the closer future. Consequently, Sessoli and her group plan to move on from the chemically stable, non magnetic gold to magnetic surfaces, now that they have evaporable SMMs ready for use. “The field of hybrid nanostructures comprising single molecules and traditional magnets is also fully unexplored and could reveal new interesting proximity effects,” says Sessoli, on the way to challenge Moore's law down to the nanometer scale.