Jan 10, 2007
Platinum nanoclusters go magnetic
Platinum atoms, which are not magnetic in the bulk, become magnetic when grouped together in small clusters, according to new experiments by physicists in Germany. The result, which confirms theoretical predictions, is not only of fundamental interest but could find applications in information storage and spintronics in the future.
Clusters of atoms form a type of matter that is intermediate between single atoms and bulk matter. Metallic clusters are widely used as catalysts because they have a very high surface-to-volume ratio, which allows them to speed up chemical reactions. Researchers believe that magnetic clusters might also be used in information storage or in spintronic devices that exploit the spin of the electron as well as its charge.
Scientists had already predicted that nanosized samples of platinum are highly paramagnetic (i.e. they are attracted to a magnet). The new experimental results, from Emil Roduner of the University of Stuttgart and colleagues, confirm these predictions and could help us to understand better how magnetism can develop in a normally non-magnetic element.
Roduner and co-workers began their experiment by preparing the platinum clusters in the pores of a zeolite – a crystalline aluminosilicate that resembles a highly regular sponge with a network of pores measuring 1.3 nm in diameter. They then stabilized the clusters in these pores so that they did not grow any further. Next the team identified the clusters using a special X-ray technique called EXAFS, which is selective for specific elements (in this case platinum) and is particularly suitable for small species like these clusters. Finally the physicists measured the magnetization of the clusters as a function of temperature and magnetic field using an extremely sensitive magnetometer known as a superconducting quantum interference device.
The Germany team found that each cluster, which consists of 13 atoms, has a magnetic moment as high as 0.65 Bohr magnetons per atom. By comparison the figure for iron is 2.2 Bohr magnetons per atom.
"The main significance of our work at this point is a fundamental understanding of magnetism," Roduner told nanotechweb.org. "However, since small, isolated, high magnetic moments - in this case corresponding to eight unpaired electrons per 13-atom cluster - are also of general interest to information storage or spintronics, these materials might be further developed to suit such advanced applications."
Another intriguing feature of the platinum clusters is that they are best described as "superatoms", said Roduner. This means that each 13-atom cluster has properties that are very similar to those of individual atoms. "It is fascinating to imagine that new periodic tables of superatoms might be drawn and that this may lead to a new chemistry of superatoms, offering a fantastic perspective for the future of young chemists," he added.
The researchers reported their work in Phys. Rev. Lett..
About the author
Belle Dumé is acting editor of nanotechweb.org