Atomic Level Storage
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
Two rows of six iron atoms can store one bit of
information - if adjacent atoms spin in opposite
these atoms are aligned in the same
directions (Image: IBM Research)
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.