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Materials

New Material For Data Storage

Spin-transition compounds prove amenable to nanoscale processing

by Mitch Jacoby
November 3, 2008 | APPEARED IN VOLUME 86, ISSUE 44

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Credit: Massimiliano Cavallini/Inst. of Nanostructured Materials
"Written" with an Fe(II) "ink," this CD data pattern features lines of submicrometer-scale length and width (blue, optical micrograph) and up to 80-nm height (orange, AFM image).
Credit: Massimiliano Cavallini/Inst. of Nanostructured Materials
"Written" with an Fe(II) "ink," this CD data pattern features lines of submicrometer-scale length and width (blue, optical micrograph) and up to 80-nm height (orange, AFM image).

A FAMILY OF COMPOUNDS endowed with a property that enables them to be switched between two magnetic states may form the basis of future high-density data-storage technologies, according to researchers in Italy and Germany. Their investigation demonstrates that molecular spin-transition compounds can be fashioned into robust micro- and nanometer-scale structures for data-storage devices (Angew. Chem. Int. Ed. 2008, 47, 8596).

In the push to increase the data-storage capacity of electronic devices, manufacturers have steadily shrunk the size of the elements that make up the patterns that represent data. For magnetic hard drives in computers, the "elements" are magnetic domains—microscopic regions of the disk surface—which are magnetized during the data-writing process in specific orientations.

Hard-drive manufacturers continue to pack more information on disks by "writing smaller," that is, by shrinking the domains. But that approach, which has led to today's nanoscale domains, cannot be continued much longer. Smaller domains are known to spontaneously lose their magnetic orientation, which would lead to data loss.

Faced with that impending size limit, researchers in various labs are pursuing alternative data-storage strategies based on the properties of much smaller entities—individual or small numbers of molecules. Spin-transition (ST) compounds, such as those based on Fe(II) species, have been proposed as candidates for such applications because their molecules can be triggered by temperature and other stimuli to switch between a diamagnetic (or low spin) and a paramagnetic (or high spin) state.

Until now, however, only limited progress has been made in developing methods for processing these compounds and "drawing" microscopic patterns with them. In addition, some of those procedures were found to adversely alter the materials' properties.

Now, Massimiliano Cavallini of the Institute of Nanostructured Materials, in Bologna, Italy; Mario Ruben of the Karlsruhe Research Center, in Germany; and coworkers have shown that an Fe(II) phenanthroline ST compound can be used to form well-ordered and durable nanoscale patterns and that the material retains its spin-flipping quality after processing.

Demonstrating the Fe(II) compound's usefulness as a nanoscale "ink," the team employed lithographic stamping methods to draw a replica of the data-storage pattern encoded on a compact disc, which consists of nanometer-thick dots and lines. On the basis of microscopy, X-ray measurements, and Raman spectroscopy, the team reports that after patterning, the material is highly crystalline and can be induced to switch between magnetic states by altering the temperature.

"This is a nice piece of work," says Daniel Ruiz-Molina of the Center for Investigation in Nanoscience & Nanotechnology, in Bellaterra, Spain. In addition to advancing fundamental science, "this pioneering work will open the door to the development of a new generation of molecule-based storage systems," he says.

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