The Dance of the Electron Spins

From Science News, May 26th, 2007; Vol.171 #21 (p. 334)

Physicists have used a novel measuring technique to track the motions of electron spins in a tiny magnet as its polarity flips, with north and south poles changing places. Magnetic data recording relies on such reversals to encode bits of data.

At the atomic level, magnetism arises from the intrinsic spin of a material’s electrons. Polarity can be flipped by applying a magnetic field to reverse the spin of each electron. The spin’s axis spirals away from its initial alignment and into its new one, says Can-Ming Hu of the University of Manitoba in Winnipeg.

Physicists usually detect this motion, called precession, by beaming finely tuned microwaves at the sample and measuring electromagnetic feedback. However, Hu says, picking up that feedback becomes increasingly difficult as the sample size shrinks.

Hu and his colleagues made use of a recently discovered phenomenon called the spin dynamo effect, in which the precession of the spins converts microwave-frequency energy into an electric current. It’s then easy to measure the current with high accuracy.

Because the spins influence each other, their precessions coordinate as dancers do in a ballet. The new experiments have revealed surprisingly complicated choreographies, Hu says. The team’s results appear in the May 25 Physical Review Letters.

Hu says that spin dynamos could someday power nanoscale electronic devices by extracting energy from microwaves.

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