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Tiny whiskers make huge memory storage

BUFFALO, N.Y., Jan. 31 (UPI) -- New, tiny magnetic sensors could help break a technical barrier to ushering in the next generation of computer disk storage capacity, researchers reported Friday.

The sensors, filaments of nickel thinner than a wavelength of visible light, are capable of detecting extremely weak magnetic fields.

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Although it is already possible to increase hard drive storage capacity many times, the process has lagged because technology has not existed to read the data signals, researcher Harsh Chopra, a materials scientist at the State University of New York in Buffalo, told United Press International.

"Now we can," he said.

The problem with expanding storage disk capacity is that as data bits become exceedingly small, their magnetic fields become correspondingly weaker and harder to read, Chopra explained. In order to read data signals reliably, the signals must produce a large enough change in the electrical resistance of the computer's magnetic sensors. The signals also must produce those changes at room temperature.

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In findings to be published in next July's issue of the journal Physical Review B, Chopra and physicist Susan Hua described sensors they have developed that are both small and sensitive to improve the density of hard drives.

The sensors are actually microscopic whiskers of nickel only a few atoms wide. Each of the filaments can read infinitesimal magnetic fields and at room temperature can detect a 100,000 percent change in voltage.

The sensors result in "much clearer signals," Chopra said.

For comparison, he explained, imagine normal magnetic sensors can read a signal that begins with a strength of 1 and swings between an "off" reading at 0.8 and "on" at 1.2. The new sensors can read a range that swings between minus 1000 and plus 1000. That degree of sensitivity means terabits of data -- or trillions of bits -- could be crammed into a square inch of disk space. About 160 terabits comprise the entire contents of the Library of Congress.

Chopra said the extreme sensitivity of the new sensors is due to a phenomenon called "ballistic magnetoresistance," or BMR.

"Normally, when electrons travel in a wire, they go in a zigzag pattern, scattered by impurities or temperature-dependent effects," he explained. "Here the conductor has become so small, the electrons travel in straight paths."

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Chopra said the ballistic electrons lead to clearer binary signals -- at least in part. However, "we don't fully understand how the signal is enhanced to such very large degrees," he said. "The existing theories don't yet explain it. There are some things here no one quite understands. That means there's a lot of science to be discovered yet."

Meanwhile, Chopra and Hua are experimenting with sensors made of other substances, such as magnetite and chromium oxide. They are using a manufacturing technique developed originally by researcher Nongjian Tao, of Arizona State University in Tempe. With it, they said, they can reproduce the sensors reliably and simply. Because the sensors remain sensitive at room temperature, they should attract industry attention quickly.

"The normal cycle for (such technologies) from discovery to implementation is about six to eight years," Chopra said.

The research is "very exciting," said K.L. Murty, director of the National Science Foundation's metals research program. "It could have a big impact on magnetic storage -- hard disks -- to put in more memory. It might also have a lot of biomedical applications," he said.

Chopra said the sensors also could be used to detect biomolecules, even in low concentrations. Each organic molecule could have its own fingerprint in terms of affecting whiskers' voltage.

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"It might only be two to three years (until we have) a working device in biomedical applications," he said.

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(Reported by Charles Choi, UPI Science News, in New York)

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