Magnetic tornadoes swirl in the nanoworld

Magnetic nanocores as data storage of the future?

Micromagnetic simulation: magnetization of the vortex-antivortex structure in the ground state (top) and after a magnetic pulse (bottom). © FZD
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Physicists have succeeded in creating unusual magnetic vortexes around three magnetic nanowires in a thin layer. With the help of subsequent investigations at a synchrotron facility, they were also able to show for the first time the unpredictable movement patterns of the three magnetic tornadoes, according to the scientists in the journal Physical Review Letters.

This year, the Nobel Prize in physics was awarded for a discovery in the field of magnetism. The Nobel Prize winners Fert / Grünberg certainly could not foresee in their basic research how fast the applications of their effect would prevail in computer hard disks.

Karsten Küpper and Jürgen Fassbender from the Dresden-Rossendorf Research Center (FZD) are also investigating fundamental physical questions about magnetism, whose potential applications can only be guessed at. Magnetic vortex structures in the nanoworld - one nanometer corresponds to one millionth of a millimeter - play a decisive role here. Since the magnetic cores are very small in the middle of the generated vortex with only about ten nanometers and the magnetization direction of the cores is also very stable, they are considered in the art as possible candidates for nonvolatile data storage of the future.

Like the wind in a cyclone

But the physicists are still interested in the fundamental phenomena of the magnetic vortex, which were discovered only a few years ago in the experiment. Imagine a very thin circular disk just a few microns in diameter, made of magnetic material. The magnetic field is circular, similar to the wind in a cyclone. In the middle of this disk exists a tiny nucleus of only about 20 atoms, which can be compared to the eye of the cyclone.

If you now apply a magnetic field from the outside, then the core moves away from the center to the edge of the disc. If the external magnetic field is abruptly released, the core moves backwards or forwards to the center of the circle on a spiral path with or against the clockwise direction. The core is characterized, in contrast to the Verwirblungen on the disc by a stable magnetic field, which is perpendicular to the disc and pointing either up or down. Such a magnetic vortex is called a vortex. There are four states of motion for each vortex: right- or left-handed magnetic swirls on the disk combined with upward or downward magnetism for the core. display

Since an anti-state exists for every physical ground state, there is also an antivortex for a vortex (comparable to particles and anti-particles). The physicists of the FZD have now for the first time succeeded in studying the movements of two vortices with an anti-vortex in a thin ferromagnetic layer. Normally, one vortex and one anti-vortex would immediately cancel each other out, but two vortexes arranged around an anti-vortex form a very stable unit.

Movement pattern of anti-vertebrae first observed

The movement patterns were studied at the "Swiss Light Source" at the Paul Scherrer Institute in Switzerland. Here, too, questions from fundamental physics were guiding: How do the magnetic cores of the two vortices and the anti-vortex influence each other in their dynamics? Do they repel each other, attract each other or destroy a vortex with an anti-vortex? ? Are movements braked or reinforced? What role do the domain walls play in the dynamics of the configuration?

Fassbender: "In particular, we were able to observe the movement pattern of anti-vertebrae for the very first time. The interaction of the three nuclei is now much better compared to simulation calculations. In addition, we have been able to determine the orientation of the magnetic field in the nucleus of the vertebrae via the respective motion patterns, although the actual nuclei are smaller than the resolution power of the microscope. "

Further research is needed

Fassbender's team will continue research into magnetic tornadoes. Next, the scientists want to try to create a single antiperspirant, whose magnetization dynamics could not yet be observed. If it then understands the properties of this one anti-vortex, it can better explain the dynamics of more complex structures.

(idw - Research Center Dresden - Rossendorf, 07.12.2007 - DLO)