CHEMICAL & ENGINEERING
NEWS OF THE WEEK OCTOBER 22. 2001 * EDITED BY JANICE LONp & STEPHEN KJ. JR^AJSKA
in calling it ferromagnetism." Makarova defends her use of the term ferromagnetism by noting that her team has observed "a finite spontaneous magnetization with the temperature dependence typical for a ferromagnetic transition."The magnitude ofthe magnetization, in her view, is not 60 so important because it depends on the percentage of magnetic HE TITLE IS AS SPARE AND why the claim of a room-tem- phase in the sample, which they Makarova riveting as it is likely to be perature carbon magnet is so hope to increase. Makarova and coworkers note controversial: "Magnetic remarkable. 'Although a handful of metal-free magnets have been that some of their samples have Carbon." A paper with that title was discovered to date," he notes, such strong magnetization that published last week in Nature "their magnetic properties occur they can be lifted off a tabletop [413,716 (2001)}. In it, an inter- only at very low temperatures." using a small metal magnet. Furnational research team reports Efforts to detect magnetic order- thermore, they report that the the serendipitous discovery of ing at room temperature and samples remain magnetic up to ferromagnetic behavior at and above in metal-free organic com- about 227 °C. The origin of this above room temperature in a pounds have been plagued by dif- magnetism, though, remains unficulties in characterizing and clear, and they are continuing to form of polymeric C60. "If confirmed, this result will reproducing the observed mag- investigate the question. Scientists are interested in represent a breakthrough in the netism, he points out. magnetism of metal-free materiThe Nature paper on magnetic developing metal-free magnets als," writes Fernando Palacio in carbon—authored by semicon- because such magnets "would be an accompanying commentary in ductor physicist Tatiana L. Ma- electrical insulators (reducing karova of Ioffe Physico-Techni- energy losses in some applicaNature. In his article, Palacio, a physics cal Institute, St. Petersburg, tions) and should be cheaper and professor at the Materials Science Russia, and her colleagues at five lighter than their metallic counInstitute of Ara- other labs —will likely face skep- terparts," according to Palacio. Makarova, however, was not gon at the Univer- ticism in the materials commusity of Zaragoza, nity. The researchers observed seeking a carbon magnet. She and in Spain, explains "strong magnetic signals" in her colleagues, including Pablo Esquinaziy'ïakovKopelevich, and 5 rhombohedralC60,a 2 polymer produced Roland Hôhne, were looking for g by subjecting C60 to signs of superconductivity in I high temperatures polymerized C60—a reasonable * and pressures. Pala- pursuit since certain fullerene is cio gives the team derivatives have been shown to t credit for excluding, be superconducting. < "up to every reasonThe discovery of unexpected able limit," the pos- magnetic behavior in an ostensisibility that impuri- bly pure carbon material leaves ties are causing the some important questions unanobserved magnet- swered, Palacio says. It thus has ism. He also believes they have "therightmix of ingredients to RHOMBOHEDRAL C 60 This two-dimensional phase demonstrated the reproducibil- be controversial."The "lively disof polymerized C60 resembles highly oriented pyrolytic ity of the effect. cussion" that will ensue, he graphite, except that instead of layers of carbon atoms, there are layers of covalently bonded C60 molecules. However, Palacio describes writes, "will help stimulate The bonding in one layer is shown at left. The the phenomenon they observed research into understanding the relationship between the polymer layers and the as "a very weak magnetization— behavior of this unusual carbon original cubic lattice of pristine C60 is shown at right. they are probably too optimistic magnet."-RON DAGANI MATERIALS
SCIENCE
ROOM-TEMPERATURE CARBON MAGNET Unexpected magnetic behavior is observed in a phase of polymerized C
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