Twisted Magnetic Fields Tie Information in a Knot: Scientific American

Twisted Magnetic Fields Tie Information in a Knot: Scientific American: Writing in Science, von Bergmann and her collaborators describe how they created skyrmions on a thin magnetic film of palladium and iron on an iridium crystal. They began with a sample in which all the atomic bar magnets were aligned. The team then used the tip of a scanning tunnelling microscope to apply a small current made up of electrons that had their spins aligned, or polarized, in a particular way. The polarized current interacted with the atomic bar magnets to twist them into knot-like configurations of skyrmions, each a few nanometers, or about 300 atoms, in diameter, says von Bergmann. The scientists could also use the polarized current to erase the knot, deleting the skyrmion...

...this is the first time that scientists have created and deleted individual magnetic skyrmions...

Artificial magnetic monopoles discovered

Artificial magnetic monopoles discovered: What happens, however, within the materials? Measurements taken by the group working under the direction of Prof. Pfleiderer in Munich using neutron scattering suggest that similar processes occur there, but individual whirls were not observed in this manner. For this reason, Stefan Buhrandt and Christoph Schütte working in Prof. Rosch's group at the University of Cologne conducted computer simulations. These showed that the whirls neighbouring the merging process observed on the surface in the experiment also occur within the materials...


Due to the fact that every whirl carries an artificial magnetic field, their creation or destruction occurs at the point of merging. "This means that an artificial magnetic monopole has to sit on this point," describes Prof. Rosch, "whenever two magnetic whirls merge in the experiment, an artificial magnetic monopole has flown through surface."

Discovery of a new magnetic order

Discovery of a new magnetic order: The existence of magnetic skyrmions was already predicted over 20 years ago, but was first proven experimentally in 2009; a group of research scientists from the Technische Universität München (TUM) had identified lattices of magnetic vortices in manganese silicon in a weak magnetic field. Unlike these structures, the ones now discovered by physicists at Jülich, Kiel and Hamburg exist without an external magnetic field and are located on the surface of the materials examined, instead of inside them. Their diameter amounts to just a few atoms, making them at least one order of magnitude smaller than the skyrmions which have been identified to date.

Vortices get organized

Vortices get organized: Skyrmions are formed on some surfaces when the spins of the electrons—think of an arrow about which each electron rotates—collectively arrange such that they wrap around the surface of a sphere (Fig. 1). This pattern spirals in such a way that the spins on the outside point up whereas those at the core point down. This collection of spins can display many properties associated with a single particle. “A skyrmion crystal is the periodic array of these particle-like entities,” explains Tokura.