Magnetic order of chains comprising iron atoms (yellow/red) on an iridium surface (blue/green) recorded by a scanning tunnelling microscope with a magnetic tip. The image shows a sample section measuring approx. 30 times 30 nanometres. This technology combined with computer simulations allowed researchers from Jülich, Hamburg and Kiel to demonstrate that the magnetic order can be selectively modulated and used to transport information. Source: Universität Hamburg/Universität Kiel/Forschungszentrum Jülich |
How
can computer data be reliably stored and read out in future when
computers are getting smaller and smaller? Scientists from Jülich,
Hamburg and Kiel propose to make use of magnetic moments in chains of
iron atoms. This would allow information to be transported on the
nanoscale in a fast and energy-efficient manner over a wide temperature
range, while remaining largely unaffected by external magnetic fields.
The researchers have demonstrated this in both theory and experiment.
Their work could pave the way for further miniaturization in information
processing. The results have been published in the latest edition of
the international scientific journal Physical Review Letters together
with a recommendation by the editor and an additional commentary.
Up
to now, computers have saved data in magnetic domains (“bits”) on the
hard drive. These domains are already inconceivably small by human
standards: a single 1 terabyte hard drive contains around eight billion
bits. However, in order to make new functionalities possible, computer
components will have to “shrink” even more in future. However, when the
bits lie too close together, their magnetic fields overlap, making the
writing and reading of data impossible. For this reason, new concepts
are required. One method of transporting data on a nanometre scale was
suggested recently by scientists at Forschungszentrum Jülich and the
universities of Hamburg and Kiel.
“To
the best of our knowledge, it is a completely new concept for data
transport on this scale,” says Jülich physicist Prof. Stefan Blügel,
director at the Institute of Advanced Simulation and the Peter Grünberg
Institute. “Because the system is extremely stable and allows
information to be transferred in a fast and energy-efficient manner, we
believe it is an extremely promising option for future applications.”
“Spin
spirals” is what the researchers call the spiral arrangement of the
magnetic properties (spins) in chains of iron atoms, which they placed
in twin rows on an iridium surface for their experiments. This is the
first time that researchers have observed such an order in an atomic
chain atom for atom. “Imagine that a spin spiral is like a screw,” says
Prof. Yuriy Mokrousov from the Jülich Institute of Advanced Simulation.
“If you hold the screw by its head and turn it, this rotation continues
right to the very tip. This means that you can work out the position of
the screw head if you know the position of the tip.”
How
spin spirals will transport data in future can be explained using a
highly simplified comparison: if you connect it at one end to a
magnetized object, then its magnetic orientation can be read out at the
other end, a few atoms and up to three hundred thousands of a millimetrer
(30 nm) further away. This would make it possible to compress
data even further and then read them out via spin spirals. “What is
particularly interesting,” says Prof. Blügel, “is the fact that the spin
of the atomic screw, which we refer to as chirality in the jargon, is
very stable—even at relatively warm temperatures.” The researchers have
tested the system for temperatures of up to 100 Kelvin.
Physically,
the spin spirals have a complex magnetic order—experts say they are
“non-collinear” because the spins of neighbouring atoms are not parallel
as is the case in simple magnetic materials. The complex order has
advantages for certain applications. For example, from the outside they
appear to possess only a small residual magnetization, which is why the
entities are not sensitive to external magnetic fields. At the same
time, however, they can be influenced to a small extent by magnetic
objects at the ends, which is important for an efficient transport of
information.
The
samples were fabricated and investigated in Hamburg. The researchers
used a scanning tunnelling microscope with a magnetic tip to measure the
magnetic structure of the sample surface. In Jülich, highly complex
computer simulations were performed to analyse the measurement data and
to understand why the spin spirals form in the first place. The
researchers now plan to investigate whether the system is also stable at
higher temperatures of up to room temperature.
Pushing Bits Through a Spin Wire
Information Transfer by Vector Spin Chirality in Finite Magnetic Chains
