Study Reveals Mechanism By Which Electronic Currents Control Magnetism (10/6/2007)

A study by University of Miami College of Arts and Science physicist Stewart Barnes and colleagues at Tohoku University in Japan describes the different mechanisms by which magnetic fields and spin-polarized electrical currents affect magnetism. The research was published in the September 21 issue of the journal Science.

Magnetic fields are commonly used to change the direction of tiny magnets on computer hard disks and in the newer spintronic devices. Such changes are the basis for information storage. But in an attempt to create faster computers by placing an ever-increasing amount of memory on computer chips, researchers found that the influence of magnetic fields becomes too weak to be effective. To get around this problem, they used a current rather than a magnetic field to do the job. The experiments were a success, and although commercial efforts exist to produce current-driven memory, the technology is not yet available to consumers.

"The use of currents to change the direction of the magnetism in nano-spintronic devices will allow us to get more Gigabits per square inch on a computer chip and, therefore, lead to faster computers," said Barnes.

Until now, it was widely believed that the mechanism by which a current induces magnetic reversal and, hence, allows information to be stored was equivalent to that of a magnetic field. In their paper, the UM-Tohoku team is the first to describe how the two mechanisms differ. By investigating the motion of magnetism at a very slow, or what is called "creep," speed the team found that, while the effect is the same, a magnetic field applies a pressure, whereas a current applies a pure turning effect, or torque.

"This work shows that a current is not just equivalent to a magnetic field, which is what many theories would have," said Barnes. This is the first study to elucidate the mechanism by which these spintronic devices work."

Note: This story has been adapted from a news release issued by the University of Miami

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