ARGONNE, Ill. (February 8, 2002) – Researchers from Bell Labs, NEC Research Institute, Inc. and Argonne National Laboratory have created an image of antiferromagnetism within a solid material, using a new technique that could lead to more cost-efficient evolution of advanced magnetic recording materials and technologies. Complete results of the research are published today in Science magazine.
In contrast to familiar magnets such as iron, antiferromagnets are difficult to identify. Just like ferromagnets, antiferromagnets contain magnetic atoms, each of which possesses a strong magnetic field. In contrast to ferromagnets, however, they are “anti,” because the fields for neighboring atoms align in opposite, rather than the same, directions. The result is that an outside observer measures zero net field, which makes it difficult to detect antiferromagnets in the same way as we do ferromagnets – namely by observing attraction or repulsion by another ferromagnet.
Because of new technological interest in antiferromagnets, there is now a greater awareness of the importance of mapping their antiferromagnetic properties. The researchers used Argonne’s Advanced Photon Source, the nation’s most brilliant source of X-rays, to watch changes in chromium, the most common metal in which antiferromagnetism is observed, as it is cooled below room temperature. “This research has extended the capabilities of the Advanced Photon Source in a way that other disciplines can take advantage of as well,” said Eric Isaacs of Bell Labs, part of Lucent Technologies, one of the authors of the research paper. “We used the Advanced Photon Source to build an X-ray microscope, allowing us to look inside materials at dimensions below one micron.” The researchers were able to capture images of the magnetic activity in a chromium single crystal at the micron scale.
“Visualizing the organization of atoms and molecules in solids allows scientists to learn more about the possibilities of the materials,” Isaacs said. “The physics and chemistry of submicron devices need to be understood to take full advantage of their potential. These are crucial building blocks for technology.” Gabriel Aeppli, senior research scientist at NEC Research Institute, added: “Historically, there have been very few practical applications of antiferromagnets, because until now they have been extremely difficult to image. The new microscope makes it dramatically easier to map out antiferromagnets and analyze their structures for practical purposes,” he said.
The researchers made X-ray images of chromium’s antiferromagnetic domains– regions in which the atomic magnetism lies along a particular direction. On cooling the chromium below -150° C (-240° F) new types of domains appear via growth from the walls between domains of a type already present at room temperature. The researchers now want to learn how the walls affect the passage of electric current, with the goal of inventing new types of nanoscale devices for computing and communications.
In addition to Isaacs and Aeppli, authors on the Science paper are Paul G. Evans of Bell Labs; and Zhonghou Cai and Barry Lai of Argonne. NEC Research Institute, founded in 1988 and based in Princeton, N.J., conducts basic research in the areas of computer and physical sciences. Its major research elements include Web computing; robust computing; intelligence; vision and language; devices; materials; optics; nano physics; biophysics, theoretical computer sciences and physics. For more information about the Institute, the Web site is at www.neci.nj.nec.com.
With more than 28,000 patents to its credit since 1925, Bell Labs is the leading source of new communications technologies, earning more than four patents every business day. Bell Labs scientists have received six Nobel Prizes in Physics, nine U.S. Medals of Science and six U.S. Medals of Technology. For more information about Bell Labs, visit its Web site at http://www.bell-labs.com.
America’s first national laboratory, Argonne conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. The University of Chicago operates Argonne as part of the U.S. Department of Energy's national laboratory system. For more information about Argonne, visit its Web site at www.anl.gov.
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Science