Smallest hard drive needs 12 atoms per bit
Scientists from IBM and the German Center for Free-ElectronLaser Science (CFEL), a group affiliated with the Max-PlanckGroup, created a data storage device that merely requires 12 atomsto store one bit of data. Key to this innovation is a techniquethat makes atom rows magnetically neutral allowing the researchersto arrange them more closely next to one another.
Press Statement
Scientists from IBM and the German Center for Free-ElectronLaser Science (CFEL) have built the world’s smallest magnetic datastorage unit. It uses just twelve atoms per bit, the basic unit ofinformation, and squeezes a whole byte (8 bit) into as few as 96atoms. A modern hard drive, for comparison, still needs more thanhalf a billion atoms per byte. The team present their work in theweekly journal “Science” this Friday (13 January 2012). CFEL is ajoint venture of the research centre DeutschesElektronen-Synchrotron DESY in Hamburg, the Max-Planck-Society(MPG) and the University of Hamburg. “With CFEL the partners haveestablished an innovative institution on the DESY campus,delivering top-level research across a broad spectrum ofdisciplines,” says DESY research director Edgar Weckert.
Data storage atom by atom
The nanometre data storage unit was built atom by atom with thehelp of a scanning tunneling microscope (STM) at IBM’s AlmadenResearch Center in San Jose, California. The researchersconstructed regular patterns of iron atoms, aligning them in rowsof six atoms each. Two rows are sufficient to store one bit. A bytecorrespondingly consists of eight pairs of atom rows. It uses onlyan area of 4 by 16 nanometres (a nanometre being a millionth of amillimetre). “This corresponds to a storage density that is ahundred times higher compared to a modern hard drive,” explainsSebastian Loth of CFEL, lead author of the “Science” paper.
Data are written into and read out from the nano storage unitwith the help of an STM. The pairs of atom rows have two possiblemagnetic states, representing the two values ‘0’ and ‘1’ of aclassical bit. An electric pulse from the STM tip flips themagnetic configuration from one to the other. A weaker pulse allowsto read out the configuration, although the nano magnets arecurrently only stable at a frosty temperature of minus 268 degreesCentigrade (5 Kelvin). “Our work goes far beyond current datastorage technology,” says Loth. The researchers expect arrays ofsome 200 atoms to be stable at room temperature. Still it will takesome time before atomic magnets can be used in data storage.
Miniaturized information storagein atomic-scale antiferromagnets. The binary representation of ‘S'(01010011) was stored in the Néel states of eight iron atomarrays
(foto: Sebastian Loth/CFEL)
First antiferromagnetic data storage
For the first time, the researchers have managed to employ aspecial form of magnetism for data storage purposes, calledantiferromagnetism. Different from ferromagnetism, which is used inconventional hard drives, the spins of neighbouring atoms withinantiferromagnetic material are oppositely aligned, rendering thematerial magnetically neutral on a bulk level. This means thatantiferromagnetic atom rows can be spaced much more closely withoutmagnetically interfering with each other. Thus, the scientistmanaged to pack bits only one nanometre apart.
“Looking at the shrinking of electronics components we wanted toknow if this can be driven into the realm of single atoms,”explains Loth. But instead of shrinking existing components theteam chose the opposite approach: “Starting with the smallest thing- single atoms – we built data storage devices one atom at a time,”says IBM research staff member Andreas Heinrich. The requiredprecision is only mastered by few research groups worldwide.
“We tested how large we have to build our unit to reach therealm of classical physics,” explains Loth, who moved from IBM toCFEL four months ago. Twelve atoms emerged as the minimum with theelements used. “Beneath this threshold quantum effects blur thestored information.” If these quantum effects can somehow beemployed for an even denser data storage is currently a topic ofintense research.
Transition from classical to quantumphysics
With their experiments the team have not only built the smallestmagnetic data storage unit ever, but have also created an idealtestbed for the transition from classical to quantum physics. “Wehave learned to control quantum effects through form and size ofthe iron atom rows,” explains Loth, leader of the Max Planckresearch group ‘dynamics of nanoelectric systems’ at CFEL inHamburg and the Max-Planck-Institute for Solid State Research atStuttgart, Germany. “We can now use this ability to investigate howquantum mechanics kicks in. What seperates quantum magnets fromclassical magnets? How does a magnet behave at the frontier betweenboth worlds? These are exciting questions that soon could beanswered.”
A new CFEL laboratory offering ideal conditions for thisresearch will enable Loth to follow up these questions. “WithSebastian Loth, one of the world’s leading scientists in the fieldof time-resolved scanning tunneling microscopy has joined CFEL,”stresses CFEL research coordinator Ralf Köhn. “This perfectlycomplements our existing expertise for the investigation of thedynamics in atomic and molecular systems.”
