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Lining Up "Nanodot" Memory

Nanoscale magnetic particles could give data storage a boost.

A more reliable way to grow magnetic nanoparticles could help create the densest form of computer memory yet. The new technique, developed by researchers at North Carolina State University, makes it possible to arrange magnetic “nanodots”–particles around six nanometers wide–in orderly arrays, making it easier to use them to store bits of information magnetically.

Join the dots: Magnetic “nanodots” made of nickel could help improve the capacity of memory chips. A new technique for growing them using lattices of titanium nitride as a template (shown here as the lighter regions) allows the dots to be organized with their magnetic fields all pointing in the same direction.

Jay Narayan, a professor of material science at North Carolina State University who led the work, says that a nanodot chip measuring one centimeter square could, in theory, store a terabit of data–50 times more than flash, the densest form of memory currently available.

Narayan’s group measured the magnetic properties of individual nanodots to show that they could hold magnetic information reliably. Talks are under way with memory manufacturers including Hitachi and Seagate to commercialize the technology, he says.

“The primary innovation is that we can keep all these dots ordered and aligned in the same way,” says Narayan. This applies not just to their physical alignment but also their magnetic orientation, which is crucial for switching their magnet states and reading them, he says.

Other researchers have created nanodots similar in size to Narayan’s. Mark Welland, head of Cambridge University’s Nanoscale Science Laboratory in the U.K., leads a group that has developed nanodots in hexagonal arrays. The trouble for Welland’s group is that the magnetic orientation of a nanodot is determined by its physical orientation; since the arrays were hexagonal, their magnetic fields were not all pointing in the same direction.

Narayan and colleagues used a novel vapor deposition technique to grow precisely aligned nanodots out of nickel. The technique, called domain-matching epitaxy, involves depositing a very thin layer of titanium nitride onto a substrate that serves as a template for the nanodots. The titanium nitride forms single crystal lattices upon which the nanodots are grown. The size of the dots and the spacing between the nanodots can be controlled by varying the growth conditions, such as the temperature.

Finding the right material was crucial, says Narayan. “We needed a metallic material that was nonmagnetic,” he says. This ensures that the templates don’t interfere with the magnetic properties of the nanodots. The technique could be used to create regular arrays of billions of nanodots.

“There is a difficulty in controlling both the size and position of the nanodots,” says Russell Cowburn a professor of nanotetchnology at Imperial College London. “Controlling this would be a huge advantage,” he says.

But Cowburn adds that growing nanodots is only part of the challenge. Making them thermally stable and finding ways to read and write magnetic information are significant challenges, he says.

For nanodot memory to be competitive, it will have to be cheap as well as dense, says Cowburn. In terms of bits per dollar, magnetic hard drives are still the cheapest form of computer memory–about 50 times cheaper than flash.

Currently, the nickel nanodots require low temperatures to function, but Narayan is working on making them out of iron-platinum, which should let them operate at room temperature.

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