Smallest magnetic memory uses just 12 atoms

Talk about doing more with less. A dozen atoms have been made to store a bit of data magnetically ? a feat normally performed by a million atoms. The work could one day help shrink the devices that store computer data.

Today's hard drives record data using a tiny electromagnet to align the spins of atoms in a metallic film that rotates below it. When the spins of about a million of these atoms are aligned in the same direction, their collective magnetic field can be detected by the electromagnet on its next pass. This means the million-strong group stores a single bit of data ? a 1 or a 0 in binary code.

Unfortunately, that collective magnetic field also affects adjacent bits, limiting how closely they can be packed. Now Andreas Heinrich of IBM Research Almaden in San Jose, California, and colleagues have made the smallest magnetic bits yet ? and they can be packed more closely together than today's much larger bits.

The trick is to make adjacent atoms spin in opposite directions. This alignment, called antiferromagnetism, does not generate an external magnetic field.

Densely packed

Using a scanning tunneling microscope, the researchers were able to encode a bit of data in just 12 iron atoms kept at a temperature just a few degrees above absolute zero. Smaller numbers of atoms were too unstable to act as bits ? without neighbours to interact with and stabilise them, the atoms behaved like quantum objects that existed in multiple spin states at once.

The team then placed eight of the 12-atom bits side by side, creating a byte of data made of 96 atoms. Because no magnetic field strayed from each cluster of 12 atoms, the bits could be placed together very closely, creating a byte 100 times as dense as those used in today's hard drives. "You can pack these things as close as you want," says Heinrich.

He says the main advance from this experiment is showing the number of atoms at which classical physics takes over from quantum mechanics at temperatures near absolute zero. Getting the same results at room temperature ? where atoms are harder to control because they jitter more ? will be a challenge. But he says one day antiferromagnets might form the basis of miniature devices that could store data much more efficiently than current hard drives.

Journal reference: Science, DOI: 10.1126/science.1214131

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