Information Technology: New Effect with Far-Reaching Consequences
Researchers have discovered a new way in which the electron spins in a material interact. The effect is active across relatively long distances and could one day play an important role in bringing about new developments in information technology. This effect is known as a chiral interaction and it is very rare in magnetic materials. In an interview, Dr. Jan-Philipp Hanke (PGI-1/IAS-1) talks about the phenomenon, which was discovered by scientists from Germany, the Netherlands, and South Korea.
What is a chiral interaction?
The term “chirality” means the concept of objects being right- or left-“handed.” It describes objects that are not identical to their own mirror image. Your own hands are a perfect example of this: the right hand is a mirror image of the left, but you can’t place one hand on top of the other so that they superpose each other.
What’s interesting about this is that chiral objects can have very different properties. A right-handed molecule, for example, could evoke the scent of oranges in your nose, while the corresponding left-handed molecule – whose molecular formula is exactly the same – produces the smell of turpentine. Left- and right-handed objects can thus be perceived differently – and influenced to a different extent – by their surroundings. This is what is known as a chiral interaction.
Where does this newly discovered effect occur?
In our research, we focused on chiral interactions that occur in certain magnetic materials in which this type of interaction is very rare. These materials are the subject of much discussion at the moment: they are known as heterostructures, and consist of a sequence of thin magnetic and non-magnetic layers. Ultimately, this new interaction leads to the formation of certain magnetic structures that have a set chirality, i.e. you either find only right-handed structures or only left-handed structures.
What practical use does this effect have?
Magnetic materials are the basis for both current and, presumably, future technologies for the processing and storage of information. Wherever larger quantities of information have to be stored or accessed, we use effects that are based on magnetic materials, for example when streaming videos or storing images. If we want to further optimize the relevant components, we have to understand how the interaction between the smallest elements – the electron spins – works.
How could this be realized in this specific case?
When it comes to the storage of information, chiral magnetic structures resulting from chiral interactions are promising for several reasons. For one thing, they are very small and could therefore conserve both energy and space.
Previously, we only knew about one chiral interaction in magnets, which has a very short range and therefore only influences electron spins that are very close to each other. On the basis of this interaction, it would theoretically be possible to construct suitable components, which would work two-dimensionally. The new interaction that we have discovered makes it possible to couple electron spins over larger distances and thus influence spins in layers that are further apart. This is absolutely decisive for having control over these chiral objects over three dimensions. And since all components are three-dimensional anyway, we can thus use them much more efficiently over all three dimensions.
Is the effect interesting from a scientific point of view as well?
Definitely. You could say we’ve found a missing piece of the puzzle. There are various known interactions in magnets that are active over short or long distances. Almost all of them, however, affect right- and left-handed objects in exactly the same way. One example is iron: the interaction of the electron spins usually has only a short range and leads to all spins aligning in the same direction. This is what ferromagnetism means. Another effect, which is produced by an interaction with a long range, is the giant magnetoresistance effect, which plays an important role in state-of-the-art storage technology to this day.
Chiral interactions, in contrast, are much rarer. Only one such interaction with a very short range was previously known to occur in magnets. The chiral interaction we discovered is thus the first that occurs over longer distances.
What triggered the discovery?
The starting point was an experiment conducted by colleagues headed by Prof. Dr. Matthias Kläui from the University of Mainz. The head of our working group here at Jülich, Prof. Dr. Yuriy Mokrousov, also works at Mainz, which led to our collaborating on the experiment.
Working with magnetic heterostructures, the experiment revealed that the two separate magnetic layers did not have the usual parallel or antiparallel alignment. Instead, there was always a slight skew. We, as theoreticians, then tried to understand this experiment using models. For this purpose, we conducted computer simulations on the JURECA supercomputer here at Forschungszentrum Jülich, for example. This allowed us to conclude that the observed skew is the signature of a chiral interaction with a long range.
What’s next for this chiral interaction?
It’s early days yet. The next step will be to optimize the materials in order to progressively enlarge the effect until we can safely say that it is ready to be brought to industry.
Further information:
Press release entitled “Concert of magnetic moments” (13.06.2019)
Peter Grünberg Institute, Quantum Theory of Materials (PGI-1/IAS-1)