Binary data

IBM stores binary data on just 12 atoms, one step closer to atomic data storage

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• published: 14 Jan 2012
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BM Research has successfully stored one magnetic bit of data with just 12 atoms of iron, and a full byte of data in 96 atoms. This represents a storage density that is at least 100 times denser than the largest hard drive platters or flash memory chips. The team, led by Andreas Heinrich of IBM Research Almaden (California), began their search for the smallest magnetic bit from the bottom up. Instead of starting with a known storage medium and looking for a way to improve it — the standard approach for industries governed by Moore's law — Heinrich and his team started from the smallest possible unit — an atom — and built their way up until the smallest, stable magnetic bit was achieved. IBM's 12-atom bit, in false color Heinrich & Co. literally built up an array of iron atoms on a copper substrate, one at a time, until the iron atoms reached "critical storage mass" — enough atoms to stably retain their magnetism. At low temperatures, this number is 12; at room temperature, the number is around 150 — not quite as impressive, but still an order of magnitude better than any existing hard drive or silicon (MRAM) storage solution. So far, so good. But how did the IBM researchers manipulate single atoms with such accuracy — and, perhaps more importantly, how did they read and write these 12-atom bits? The answer, as with many modern feats of nanoengineering, is a scanning tunneling microscope (STM). An STM is a room-sized device with a very, very tiny tip that can image, measure, and manipulate structures at an atomic level using a small electric current. Antiferromagnetism used to store a binary bitFirst the STM is used to arrange the iron atoms on the copper substrate — a relatively easy task, Heinrich tells us. Then the STM is used to measure the magnetism of a given atom to see if the magnetic bit has a binary value of 0 or 1. This is slightly trickier than it sounds and requires the use of antiferromagnetism. On a hard drive, which uses ferromagnetism, every atom of a magnetic bit faces the same direction, creating a magnetic field ("north", "south") that is measured by the head and turned into a binary value. The problem with this is that you need thousands or millions of ferromagnetic atoms to create a large enough magnetic field. With antiferromagnetism, the atoms of a magnetic bit are aligned in such a way that the sum magnetic field is zero. This is hard to describe — it's easier if you just look at the picture on the right, or watch the video embedded below. With an antiferromagnetic bit, if you flip a single iron atom with an STM, every other atom switches to maintain the equilibrium. Because of this, you look at the top left atom of the magnetic bit (using an ST) and instantly work out the binary value. Voila — a 12-atom magnetic bit that you can read and write. The challenge now, though, is to find a way of mass-producing sheets of copper with arrays of precisely-aligned iron atoms. You wouldn't technically need a room-sized STM to manipulate these atom-sized bytes, but we would need to find a way of attaching wires to these tiny structures, which are well beyond state-of-the-art 22nm semiconductor tech. Fortunately for Heinrich, when your job title is Lead Investigator of Atomic Storage, you don't have to bother yourself with such minutia — you can leave that to the dimwitted nanotech flunkies to sort out.