Magnetic random access memory stores bits
of information magnetically rather than electronically, allowing this
type of chip to retain data after the computer is turned off. Researchers
are working on magnetic random access memory chips that hold as much data
as standard electronic memory chips.
The challenge in making nanoscale magnetic memory elements suitable
for high-capacity memory chips is controlling the magnetic switching of
such tiny memory cells. In recent years researchers have found that a
promising design is a nanowire bent into a circle. Magnetic rings have
two stable magnetic states that can store 1s and 0s -- magnetic fields
circulating clockwise, and magnetic fields circulating counterclockwise.
The key to making stable magnetic memory rings is introducing
a small asymmetry in the ring. It is difficult to manufacture nanoscale
rings that are asymmetric, however.
Researchers from the University of Illinois at Chicago have found
that square rings, which are easier to produce because straight lines
are less difficult to etch the nanoscale than curves, could solve the
problem. The researchers showed that the asymmetry inherent in rectangles
is enough to yield the stable magnetic states needed for random access
The researchers' prototype rings measured 1.5 by 1 microns, or
thousandths of a millimeter, which is much larger than practical magnetic
random access memory. Their eventual goal is to produce rings that measure
less than 0.1 microns across. In theory, the smallest possible rings could
store 400 gigabits per square inch, according to the researchers. Four
hundred gigabits is the capacity of about 10 and a half DVDs.
The work appeared in the August 2, 2004 issue of Nanotechnology.
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