Challener et al., Nature Photonics, Advance Online Publication (22 March 2009)

Nifty. A nano-sized gold antenna called a near-field transducer, or NFT, could make for supersharp laser beams and high-capacity disk drives.

When Frying the Hard Drive Is a Good Thing

For those whose computer hard drives can never hold too much data, here's some good news. Researchers report finding a way to potentially boost disk capacity to 10 times the current theoretical limit--and without a correspondingly astronomical increase in cost.

Ever since the dawn of desktop computers, the data-storage industry has struggled to keep up with relentless consumer demand for greater capacity. But industry experts predict that standard, magnetic hard drives could reach their storage limit in about 5 years.

The problem has to do with how today's devices are made. Computer hard drives contain a thin film of tiny magnetic particles. Magnetic recording heads then interact with the particles as the disk spins rapidly, affixing 1 bit of data to 100 of the particles or so and arranging the bits in spiraling rows, just like old-fashioned vinyl records. Over the years, disk manufacturers have increased data-storage capacity by packing those rows together ever more tightly; today, they're separated by only a few hundred nanometers, or billionths of a meter. The problem is that as the grains grow smaller, they also grow magnetically weaker. At some point, even changes in room temperature will interfere with their ability to maintain their magnetic alignment and hold data reliably.

One possible solution is to abandon magnetic data-storage disks entirely, instead using an optical medium similar to CDs or DVDs. But they couldn't match the existing industry standard for data-storage density.

A team at Seagate Technology, a hard-drive manufacturing company in Pittsburgh, Pennsylvania, wondered if it would be better to combine lasers with magnetic heads. Based on an idea developed in the 1990s, they reasoned that if the magnetic grains could be heated while receiving data bits, they could be made more stable. So the team developed a test magnetic recording head that also contained a new device called a near-field transducer (NFT)--sort of an optical antenna. Mounted on a computer's magnetic recording head, the NFT can focus a laser beam inside an area less than 75 nanometers in diameter, or one-tenth as wide as the narrowest conventional laser beam. That's sharp enough to fire up the individual magnetic grains just as they are receiving data bits.

As the Seagate researchers reported online this week in Nature Photonics, when the grains cool down, the laser heating stabilizes their magnetic alignment, enabling the grains to hold data indefinitely. This means that diskmakers could pack the grains into much tighter rows, thereby greatly increasing data-storage space.

So far, the Seagate team has managed to match only the industry standard of 250 gigabits per square inch. "There are still many engineering problems to solve," including delivering laser light to the recording head efficiently, says electrical engineer and lead author William Challener. Still, that's the best number seen so far for the new prototype storage techniques, notes physicist and electrical engineer Randall Victora of the University of Minnesota, Twin Cities. Challener says his team will continue to perfect the heat-assisted recording method until current data-storage technology runs out of steam. That will "give us the time we need to develop the manufacturing technology," he says.

Posted in Math