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Magnetic thin films yields more efficient data storage

Posted: 21 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:ferromagnets? data storage?

A newly discovered magnetic phenomenon could lead to much faster, denser and more energy-efficient chips for memory and computation. The findings, reported in the journal Nature Materials, could reduce the energy needed to store and retrieve one bit of data by a factor of 10,000, says the paper's senior author, Geoffrey Beach, an assistant professor of materials science and engineering at Massachusetts Institute of Technology (MIT).

It turns out the key to this phenomenon lies not in the magnetic materials themselves, but in what's next to them: In this case, the team used very thin films of a ferromagnetic material, deposited on a metal base, and with a layer of an oxide material on top-a sort of ferromagnet sandwich. The behaviour of the ferromagnetic layer, it turns out, depends on the metal that layer rests upon.

Ferromagnetic materials, including the familiar bar magnets, have a north and a south pole. When such materials are used for data storage, such as on a computer's hard disc, separate tiny "domains" on their surface can have these poles pointing either up or down, representing ones and zeros. Normally, when a ferromagnetic material is exposed to a current, these domains are pushed along the surface in the same direction as the electron flow.

But previously, in rare cases, the movement was in the opposite direction, puzzling researchers. The MIT team found that when the thin ferromagnetic film was deposited on a slab of platinum, it exhibited this backward flow-which Beach likens to being dragged upwind.

chiral ferromagnets

Figure 1: MIT researchers discover efficient control of magnetism in chiral ferromagnets.

But under circumstances that were identical, except that the film was deposited on the metal tantalum, the magnetic domains flowed in the normal direction-meaning that the key was not in the ferromagnet itself, but in its next-door neighbour. Both platinum and tantalum are nonmagnetic, so they would not ordinarily be expected to affect magnetic behaviour.

It turns out that in either case, an unexpected effect alters how magnetic domains switch from one orientation to the other. Normally, when the spin orientation changes from one domain to the other (say, from "up" to "down"), the direction of that change is random. But in these thin-film sandwiches, spin rotations are aligned, consistently either turning clockwise or counterclockwise. The researchers showed that because of this peculiar effect, current can push domains with much more force than in conventional materials, and the direction that the domains move can be engineered simply by selecting the nonmagnetic metal underneath the magnet.

Such asymmetrical behaviour is called a chiral effect; the researchers say this is the first demonstration of chiral behaviour in magnetic domains.

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