IBM researchers have created a magnetic film containing tiny magnetic particles--each just 4 nanometers across--that could be the basis of a new generation of hard disk drives. The films may have the potential to hold terabytes of data per square inch, hundreds of times the capacity of today's disk drives.
To produce a current hard disk, manufacturers essentially spray-paint a cobalt-alloy onto a surface under vacuum and bake it, leaving a material full of 15- to 20-nanometer grains. To store one bit of information, a recording head typically aligns the magnetic orientation of several hundreds of such grains. By shrinking the grains, engineers have recently managed to increase data storage capacity a staggering 100% a year. But shrinking grains much smaller will be difficult. Many materials lose their magnetic behavior when particles shrink below about 10 nanometers, and particles that do maintain their strong magnetic behavior tend to clump together instead of forming an even sheet. Hence, industry experts fear they won't be able to keep up the blistering pace much longer.
Shouheng Sun of IBM's T. J. Watson Research Center in Yorktown Heights, New York, and his colleagues managed to get around both problems at once by making tiny particles from iron and platinum, which start out as weakly magnetic--allowing them to form an array--and then transforming them into stronger magnets at the end.
First, the researchers concocted a solution that included two metal salts--one containing iron atoms, which are hungry for electrons, the other platinum atoms capable of donating electrons. As the salts dissolved, the iron atoms turned to the platinums for electrons, causing the atoms to begin assembling themselves into a ball. Also in the brew were soap molecules, oleic acid, and oleyl amine.
As the particles grew, the soap molecules in the brew glommed onto the metal particles and stopped them growing at 4 nanometers. Next, the IBM team simply poured the particles out of the beaker. As the solvent evaporated, the particles nestled down into a regular structure like oranges stacked in a box. Then they baked their array at 500°C for about 30 minutes, fusing the organic molecules into a hard carbon coat that locked the particles in place.
The new materials can store data faithfully at a density equivalent to that of today's hard disks, the team writes in the 17 March Science. The particles' small size may even allow them to boost that density 10-fold using current read and write heads. But if these heads can be improved to manipulate magnetic fields on single particles--and that's a big if--then the films could potentially store orders of magnitude more data.
Sun is quick to point out that the new materials need more work before they hit the market. Still, "this is a big deal," says Jim Heath, a chemist and nanoparticle expert at the University of California, Los Angeles. "It means that magnetic recording could be carried down to near molecular length scales."