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August 3rd, 2007
Changing the rings: a key finding for magnetics design
Researchers at the National Institute of Standards and Technology's Center for Nanoscale Science and Technology (CNST) have done the first theoretical determination of the dominant damping mechanism that settles down excited magnetic states—"ringing" in physics parlance—in some key metals. Their results, published in the Physical Review Letters ("Identification of the Dominant Precession-Damping Mechanism in Fe, Co, and Ni by First-Principles Calculations"), point to more efficient methods to predict the dynamics of magnetic materials and to improve the design of key materials for magnetic devices.
The ability to control the dynamics of magnetic materials is critical to high-performance electronic devices such as magnetic field sensors and magnetic recording media. In a computer's magnetic storage—like a hard disk—a logical bit is represented by a group of atoms whose electron "spins" all are oriented in a particular direction, creating a minute magnetic field. To change the bit from, say, a one to a zero, the drive's write head imposes a field in a different direction at that point, causing the electrons to become magnetically excited. Their magnetic poles begin precessing—the same motion seen in a child's spinning top when it's tilted to one side and begins rotating around a vertical axis. Damping is what siphons off this energy, allowing the electron spins to settle into a new orientation. For fast write speeds—magnetization reversals in a nanosecond or faster—a hard disk wants strong damping.
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