Information stored by a chain of magnetic atoms. Left: an STM tip measures the magnetic state of the iron atoms. Right: through increasing the current between tip and atoms the magnetic states can be switched. Peaks become valleys and vice versa. (c) Science Magazine
I now finally got the time to follow-up on last week’s paper in Science by Andreas Heinrich‘s group at IBM on magnetic storage elements that are only a few atoms in size. There have been a few misconceptions in some of the news reports with some being plainly wrong (‘smallest storage device ever made’), and many didn’t mention much about the scientific principles behind this study, although these are quite interesting. One of the better reports appeared in the New York Times, albeit again without going much into details. So I hope I can still add something useful with this blog post.
And actually, we’ve come across Andreas Heinrich’s previous research before, he does very innovative research with scanning tunneling microscopes (STM). In this latest Science paper he has now explored the limits of magnetic storage devices. Magnetism is of course the basis for storage such as magnetic hard drives. The problem in increasing the storage density in any magnetic storage device is that the magnetic regions begin to interfere with each other as they become smaller and are integrated closer together, because magnetic states on the order of just a couple of atoms are not very stable. [...]
Fridge magnets, and related magnets used in homes and offices, are made from the ceramic BaFe12O19, whose annual commercial production reaches 830,000 tons a year. Contrary to what their mundane use suggests, the physics of these magnets is rather unusual. They belong to a rare class of materials whose magnetism can be controlled with electric voltages and vice versa, which offers a new way of controlling magnetic fields in applications such as information storage (other than putting notes up on your fridge!).
Unfortunately, in most of these ceramics such effects are confined to low temperatures and have been mainly of interest to physicists only. Tsuyoshi Kimura and colleagues from Osaka University may now have changed this. They have discovered that in a close relative of fridge magnets, Sr3Co2Fe24O41, coupled interactions between magnetic and electric properties occur even at room temperature. “This demonstrates that such magnets can be used for other practical usages,” says Kimura. Their work is published online this week in Nature Materials.