An experimental breakthrough that could dramatically increase the capacity, speed and reliability of computer hard drives has been announced by an international team of physicists.
Guido Meier at the University of Hamburg in Germany and colleagues used nanosecond pulses of electric current to push magnetic regions along a wire at 110 metres per second - a hundred times faster than was previously possible.
By contrast, today's hard drives rely on the much slower spinning motion of a disk to move magnetic regions - and the data encoded by these regions - past a component that can change or "read" this magnetic information.
"If you want to make a hard drive, operating speed is an important factor," says Meier. "The idea is also to get rid of the mechanical parts, so there's much less wear and tear, and devices can become more robust."
The idea of moving magnetically-stored data electronically has been touted before. Stuart Parkin at IBM Almaden Research Center in San Jose, California, patented a similar concept called a magnetic "racetrack" in 2004.
Round the bend
In his device, a U-shaped magnetic nanowire is embedded into a silicon chip. Magnetic domains are then moved along the wire by pulses of polarised current, and are read by fixed sensors arranged in the silicon itself.
According to IBM, this type of magnetic memory could vastly simplify computers, and eventually replace all hard-disk drives. However, previous experiments have disappointed, producing speeds up to a thousand times slower than predicted.
Aligned atoms
By switching powerful magnetic fields on and off, the researchers were able to rapidly create magnetic domains in a wire less than a micron wide made of permalloy - a magnetic material made of iron and nickel that is often found in disk drives.
These regions contains many magnetic atoms all aligned in the same direction and are separated by domain walls – thin regions where the atoms change their magnetic orientation from one alignment to the other. These can then be moved using much shorter nanoscale pulses.
A powerful x-ray microscope, capable of resolving features as small as 15 nanometres, was then used to read this information by snapping images of domain walls before and after the nanosecond current pulses. Future hard drives could store data by designating a domain wall to be a binary one, while its absence could be interpreted as a binary zero, the researchers say.
However, there are still problems that need to be overcome before the technique could be used more widely. In particular, small crystal imperfections in the wire impede progress, slowing down some domain walls and stopping others altogether.
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