Sebastian Loth, Susanne Baumann, Christopher P. Lutz, D. M. Eigler, Andreas J. Heinrich, all of whom are affiliated with IBM Research- Alamaden, San Jose, CA, and some of whom are afilliated with the Max Planck Research Group-Dynamics of Naonelectronic Systems, and the Department of Physics, University of Basel, published "Bistability in Atomic-Scale Antiferromagnets," Science, Vol. 335, no. 6065, 196-199. DOI: 10.1126/science.1214131
The authors built the world's smallest magnetic data storage unit, which uses just twelve atoms per bit, the basic unit of information, and squeezes a whole byte (8 bits) into as few as 96 atoms. For comparison, in 2012 a hard drive uses more than half a billion atoms per byte.
"The nanometre data storage unit was built atom by atom with the help of a scanning tunneling microscope (STM) at IBM's Almaden Research Center in San Jose, California. The researchers constructed regular patterns of iron atoms, aligning them in rows of six atoms each. Two rows are sufficient to store one bit. A byte correspondingly consists of eight pairs of atom rows. It uses only an area of 4 by 16 nanometres (a nanometre being a millionth of a millimetre). 'This corresponds to a storage density that is a hundred times higher compared to a modern hard drive,' explains Sebastian Loth of CFEL, lead author of the "Science" paper.
"Data are written into and read out from the nano storage unit with the help of an STM. The pairs of atom rows have two possible magnetic states, representing the two values '0' and '1' of a classical bit. An electric pulse from the STM tip flips the magnetic configuration from one to the other. A weaker pulse allows to read out the configuration, although the nano magnets are currently only stable at a frosty temperature of minus 268 degrees Centigrade (5 Kelvin). 'Our work goes far beyond current data storage technology,' says Loth. The researchers expect arrays of some 200 atoms to be stable at room temperature. Still it will take some time before atomic magnets can be used in data storage.
First antiferromagnetic data storage
"For the first time, the researchers have managed to employ a special form of magnetism for data storage purposes, called antiferromagnetism. Different from ferromagnetism, which is used in conventional hard drives, the spins of neighbouring atoms within antiferromagnetic material are oppositely aligned, rendering the material magnetically neutral on a bulk level. This means that antiferromagnetic atom rows can be spaced much more closely without magnetically interfering with each other. Thus, the scientist managed to pack bits only one nanometre apart" (http://www.desy.de/information__services/press/pressreleases/@@news-view?id=2141&lang=eng, accessed 01-12-2012)