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Tailor-Made Nanomagnets

Researchers from Jülich and Hamburg assemble magnetic structures - atom by atom

Jülich, 3 May 2012. Tiny magnets made up of only a few atoms could provide the foundation for future information technology, making it faster and less energy-consuming with new functionalities. Based on existing knowledge of the physical interactions between atomic building blocks, Jülich and Hamburg researchers have now demonstrated how such nanomagnets can be tailor-made with a defined magnetic structure. The results of their work have been published in the current issue of the renowned journal “Nature Physics” (DOI 10.1038/NPHYS2299).

In 1959, Richard Feynman, one of the most famous theoretical physicists of all times and later Nobel laureate, asked his colleagues at the American Physical Society the following question: “Why cannot we write the entire 24 volumes of the Encyclopaedia Brittanica on the head of a pin?” What sounded like science fiction then was the beginning of a development which is anything but complete even today. In 1982, atoms were imaged individually for the first time, and in 1989, scientists at IBM first succeeded in spelling out letters with individual atoms.

Researchers from Jülich and Hamburg have now achieved a new breakthrough. They assembled magnetic arrays atom by atom, and measured their magnetic properties, also atom by atom. At the University of Hamburg, the researchers used a magnetically sensitive type of scanning tunnelling microscopy to arrange three to twelve iron atoms each on a copper surface to form atomic chains, flowers, and stars, and to examine these structures. The miniature “jigsaws” are highly relevant for basic research, because they can be used to verify theories. Even if the researchers’ investigations currently take place at extremely low temperatures, tiny magnets made up of only a few atoms could one day provide the foundation for information technology, making it faster and less energy-consuming with new functionalities.

“For this, it is necessary to tailor nanomagnets with clearly defined properties,” says Jülich physicist Prof. Stefan Blügel, director at the Institute of Advanced Simulation and the Peter Grünberg Institute. The researchers have now taken a first step in that direction. They were able to reliably predict the magnetic properties of their nanomagnets based on existing knowledge on physical interactions. To this end, they used a method of theoretical physics developed at Jülich.

In doing so, they confirmed what had been only an assumption: the shape in which the atoms are arranged, the number of atoms and the distance between them all have a decisive impact on the magnetic properties of the nanomagnets. A chain made up of four atoms has different magnetic properties than one made of five, and atomic flowers have different ones yet again. “One could say that each shape has its own magnetic personality,” says Dr. Samir Lounis, who heads a young investigators group at Jülich’s Peter Grünberg Institute. This is totally different than in the macroscopic world, where pieces of iron always have the same magnetic properties, whether they are ball-shaped or cube-shaped.

With the help of the method developed at Jülich, the researchers found out that all the interactions between all the atoms of a nanomagnet must always be taken into account, not only those between neighbouring atoms. “With the interactions, it’s a little bit like a game of chess,” says Jülich physicist Prof. Stefan Blügel, director at the Institute of Advanced Simulation and at the Peter Grünberg Institute. “In order to win, it is not enough to keep a close eye on those pieces of your opponent that are close to your own, you have to bear in mind lots of possible moves, even of pieces that are further away.”

For the calculation of the properties of nanomagnets, this means that as soon as an atom is added or removed, the magnetic properties of the entire magnet change radically. For each new shape, the researchers must calculate the interactions between all the iron atoms. Since the computing power required increases drastically with the number of atoms, this limits the size of structures that can be predicted. The researchers are now examining how such computational processes can be made even faster, so that in future, it will be possible to simulate thousands of atoms.

Atom-by-atom engineering and magnetometry of tailored nanomagnets;
A. A. Khajetoorians et al.; Nature Physics (2012); DOI: 10.1038/NPHYS2299

Nanostrukturen The picture shows magnetic nanostructures on a copper surface. Researchers from Jülich and Hamburg assembled them from individual iron atoms (cones). For this purpose, they used a magnetically sensitive form of scanning tunnelling microscopy. By this method, they also determined the magnetic orientation of the iron atoms, marked in different colours in the picture (blue = downward spin, yellow = upward spin).
Copyright: Universität Hamburg

Weitere Informationen:
Forschungszentrum Jülich:
Press release from the University of Hamburg (in German):
Research at Quantum Theory of Materials (PGI-1/IAS-1):
Research at the “Funsilab” Young Investigators Group:
Research at the Institute of Applied Physics at the University of Hamburg:

Dr. Samir Lounis, Forschungszentrum Jülich, Quantum Theory of Materials
tel. 02461 61-4068

Press contact:
Angela Wenzik, science journalist, Forschungszentrum Jülich
tel. 02461 61-6048