Researchers at an American university have produced a nanoscale device that can sense magnetic fields more than a hundred times weaker than current techniques allow. If applied to hard disks this could increase storage by a factor of up to a thousand, they claim, effectively turning today's 200-gigabyte disks into 200-terabyte devices.
Susan Hua and Harsh Deep Chopra, both professors at the State University of New York at Buffalo, say that the new system uses an effect called ballistic magnetoresistance. Most importantly, it works well at room temperature and would be easy to integrate with current disk drive manufacturing.
The sensors are made from nanometre-sized nickel whiskers strung between two much larger nickel electrodes. The whiskers are so fine that electrons have to travel in a straight 'ballistic' line across them, as opposed to the normal drunken stagger that goes on in thicker conductors. Because of this restriction, even small magnetic fields have a large effect on the ease with which the electrons move. Although this effect has been known for some time, Hua and Chopra claim to have invented a way to efficiently and repeatedly produce devices with known parameters.
"We first saw a large effect of over 3,000 percent resistance change in small magnetic fields last July," Chopra said in a statement. "That was just the tip of the iceberg. These results point to the beautiful science that remains to be discovered." He also said that the same technique may be useful in medicine, by detecting the unique magnetic signature of biological molecules in solution.
A disk drive stores bits on its surface as a pattern of magnetic fields. As the bits get smaller, the storage density per square centimetre gets higher but the strength of each individual magnetic field gets weaker. The ability of existing sensors to reliably read weak fields is one of the major limiting factors in making larger hard disks, although density has been doubling each year since 1997. At this rate, the one-petabyte -- one-million-gigabyte -- disk will arrive shortly before 2010: by comparison, the world disk drive production in 1995 totalled 20 petabytes.
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