Lattice of magnetic vortices

August 01, 2011

This release is available in German.

Physicists at Hamburg and Kiel University and the Forschungszentrum Jülich have found for the first time a regular lattice of magnetic skyrmions - cycloidal vortex spin structures of exceptional stability - on a surface. This fascinating magnetic structure was discovered experimentally at the University of Hamburg by spin-polarized scanning tunnelling microscopy and imaged on the atomic scale. Theoreticians at the Christian-Albrechts-Universität zu Kiel and the Forschungszentrum Jülich were able to explain this magnetic state with the help of quantum mechanical calculations performed on supercomputers. As the scientific magazine Nature Physics reports online on July 31, 2011, the researchers discovered the magnetic skyrmions, which consist of 15 atoms, in an atomic layer of iron on the surface of an iridium crystal. This discovery could give new impetus to the area of spintronics.

About 50 years ago the theoretical physicist, Tony Skyrme, studied quantum mechanical field theories and to his surprise found stabile and localized configurations that interact with each other and can arrange themselves in a lattice in the same way as atoms. Due to these properties he identified these vortex-like solutions as elementary particles. These skyrmions named after their discoverer later appeared in many different fields of physics and developed into an important concept. The possible formation of skyrmions in magnetic materials had already been predicted 20 years ago and was also confirmed experimentally in bulk materials.

The magnetic skyrmion lattice discovered in Hamburg occurs in an atomically thin film on a surface. The diameter of the vortices is only a few atoms and is thus at least one order of magnitude smaller than the previously known magnetic skyrmions. As it is often the case chance also played a major role in this discovery. "It is known that iron can sometimes form unusual magnetic structures. Still it was a great surprise when we found this almost square magnetic structure on the nanometer scale which is not really compatible with the hexagonal system of the iron atoms", said Dr. Kirsten von Bergmann, member of the experimental research group headed by Prof. Roland Wiesendanger in Hamburg. The fact "that a sophisticated variation of the experimental setup gives data that can be compiled to yield the complicated magnetic structure" fascinates also Matthias Menzel, a postgraduate student.

In order to understand this intriguing spin structure and the exceptional symmetry breaking between magnetic and atomic order, the theoreticians at the University of Kiel and the Forschungszentrum Jülich had to develop a model for the spin structure and carry out complex quantum mechanical calculations on supercomputers at Jülich. These provided the confirmation that stable magnetic skyrmions form on this metal surface. Professor Stefan Heinze, Head of the research group in Kiel: "With the help of our model we were able to specify the precise spin structure in the iron film and identify it as a skyrmion lattice. The comparison with the experimental data provided the ultimate proof for our discovery."

The interplay of various magnetic interactions is the cause for the occurrence of this complex structure. While the canting of atomic spins with a certain rotational sense is caused by the antisymmetric Dzyaloshinskii-Moriya interaction, the skyrmions found here can only be induced by the so-called four-spin interaction with the participation of four magnetic atoms.

The magnetic skyrmions found open up completely new possibilities for future applications, for example in the field of spintronics, but at the same time raise new questions: How does electric current interact with the skyrmions and can we deliberately move the magnetic vortices in a specific manner?
Original publication: Spontaneous atomic-scale magnetic skyrmion lattice in two dimensions Stefan Heinze, Kirsten von Bergmann, Matthias Menzel, Jens Brede, André Kubetzka, Roland Wiesendanger, Gustav Bihlmayer, Stefan Blügel, Nature Physics, online publication of 31 July 2011, DOI: 10.1038/NPHYS2045

One photo on this topic is available for download: Illustration: The tiny cycloidal vortices composed of only approximately 15 atoms form a regular, almost square lattice. In the right section of the illustration the magnetic measurement by spin-polarized scanning tunnelling microscopy is shown as a gray-scale image. The square cutout represents a single skyrmion. The colored cones show the magnetic direction of the individual, hexagonally arranged iron atoms of the metal film.
Picture credits: M. Menzel, University of Hamburg


Dipl.-Chem. Heiko Fuchs (Public Relations)
Collaborative Research Centre 668
ERC Advanced Grant FURORE
University of Hamburg
Institute for Applied Physics
Jungiusstr. 9A, 20355 Hamburg
Tel.: +49 (0)40 42838-6959
Fax: +49 (0)40 42838-2409

Prof. Dr. Stefan Heinze
Christian-Albrechts-Universität zu Kiel
Theoretical Physics
Tel.: +49 (0)431 880-4127

Kiel University

Related Physics Articles from Brightsurf:

Helium, a little atom for big physics
Helium is the simplest multi-body atom. Its energy levels can be calculated with extremely high precision only relying on a few fundamental physical constants and the quantum electrodynamics (QED) theory.

Hyperbolic metamaterials exhibit 2T physics
According to Igor Smolyaninov of the University of Maryland, ''One of the more unusual applications of metamaterials was a theoretical proposal to construct a physical system that would exhibit two-time physics behavior on small scales.''

Challenges and opportunities for women in physics
Women in the United States hold fewer than 25% of bachelor's degrees, 20% of doctoral degrees and 19% of faculty positions in physics.

Indeterminist physics for an open world
Classical physics is characterized by the equations describing the world.

Leptons help in tracking new physics
Electrons with 'colleagues' -- other leptons - are one of many products of collisions observed in the LHCb experiment at the Large Hadron Collider.

Has physics ever been deterministic?
Researchers from the Austrian Academy of Sciences, the University of Vienna and the University of Geneva, have proposed a new interpretation of classical physics without real numbers.

Twisted physics
A new study in the journal Nature shows that superconductivity in bilayer graphene can be turned on or off with a small voltage change, increasing its usefulness for electronic devices.

Physics vs. asthma
A research team from the MIPT Center for Molecular Mechanisms of Aging and Age-Related Diseases has collaborated with colleagues from the U.S., Canada, France, and Germany to determine the spatial structure of the CysLT1 receptor.

2D topological physics from shaking a 1D wire
Published in Physical Review X, this new study propose a realistic scheme to observe a 'cold-atomic quantum Hall effect.'

Helping physics teachers who don't know physics
A shortage of high school physics teachers has led to teachers with little-to-no training taking over physics classrooms, reports show.

Read More: Physics News and Physics Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to