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ORNL researchers win Materials Sciences Award from Department of Energy
OAK RIDGE, Tenn., April 1, 1996 Using parallel computers in the Center for Computational Sciences at the Department of Energy's (DOE's) Oak Ridge National Laboratory (ORNL), scientists better understand a physical effect that already has magnetic appeal: it allows more data to be packed on computer disks. Their achievement of greater understanding of the giant magnetoresistance (GMR) effect has earned them a prestigious DOE award.
For their outstanding research, Bill Butler of ORNL's Metals and Ceramics, Xiaoguang Zhang and Don Nicholson of the Computational Physics and Engineering Division, and Thomas Schulthess of DOE's Lawrence Livermore National Laboratory received the DOE-Basic Energy Sciences Division of Materials Sciences Award for Outstanding Scientific Accomplishment in Metallurgy and Ceramics for 1995. Only two other such awards were given for 1995.
Discovered in France in 1988, GMR is a large change in a magnetic material's electrical resistivity caused by an applied magnetic field. Resistivity is a material's resistance to the flow of electrical current. It was found then that resistivity of a layered iron-chromium film was lowered when the material was placed in a magnetic field. This effect allows GMR "read sensors" to read data crammed into high-density disks as tiny regions of magnetization (the extent to which the material is magnetized).
By working at the atomic level, performing first-principle calculations of variations of electrical resistivity in metal alloys, ORNL researchers hope to improve magnetic storage systems. They have been working with IBM on the use of GMR to make higher-density disk drives.
This research in the Metals and Ceramics Division and the Computational Physics and Engineering Division uses advanced computing techniques to model the GMR effect in materials that have structures "layered" at the atomic scale. In these structures, the decrease in electrical resistivity occurs when the directions of magnetic moments of two layers are aligned by an external magnetic field.
"We used the Kendall Square Research and IBM SP2 parallel computers to calculate conductivity, the inverse of resistivity," Butler says, "and we are using the Intel Paragon XP/S 150 to calculate the magnetic fields required to align fields in the magnetic layers. We were interested particularly in systems in which copper layers are embedded in cobalt."
Their calculations showed a waveguide effect for electrons in the cobalt-copper system.
"Like light waves moving a long distance in a properly made optical fiber for telecommunications," Butler says, "some of the electrons can travel far in copper without being scattered because they are trapped in the copper, which has lower resistivity than cobalt. When we compared our calculations with measurements at the IBM Almaden Research Center, we concluded that if methods could be developed to make smoother interfaces between the alternating layers of cobalt and copper, exciting applications would follow.
"For example, it would be possible to make computer operating memory, or random access memory, that is immune to power disruptions and ionizing radiation. GMR motion sensors could be developed to increase the efficiency and safety of our home appliances, automobiles, and factories. Magnetoelectronic devices may someday complement or even replace semiconductor electronic devices."
The research was sponsored by DOE's Office of Defense Programs Technology Transfer Initiative, through a cooperative research and development agreement with IBM, and by DOE's Office of Energy Research, Basic Energy Sciences.
ORNL, one of the Department of Energy's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Research Corp.