Saving Data in Vortex Structures

Photo: A grid of magnetic vortex structures

Three years ago Professor Christian Pfleiderer and his team from the physics department at the TUM discovered an entirely new magnetic structure in a silicon manganese crystal – a grid of magnetic eddies. Together with the team of Professor Achim Rosch from the University of Cologne, he studied the properties of these eddies, so-called skyrmions, named after the British physicist Tony Skyrme, who predicted their existence 50 years ago. They were expecting results in the field of so-called spintronics, nano-electric components that utilise not only the electric charge of electrons for processing information, but also their magnetic momentum, known as spin.

While Peter Grünberg and Albert Fert received the Nobel Prize in 2007 for work on significantly faster data readout, research today concentrates on the question of how magnetic information can be written directly to materials via electric current. However, the extremely strong electric currents required produce side effects, which are practically untameable, even in nano-structures. Since skyrmions can be moved with 100,000 times less current, interest has been aroused in both the scientific community and in industry.

Although magnetic eddies were discovered in silicon manganese it was clear that it would not remain the only material capable of generating skyrmions. This has turned out to be true. Meanwhile, Japanese researchers have proven that individual eddies can be generated, and a group of physicists from the Research Centre Jülich, as well as the Universities of Hamburg and Kiel, provided evidence that magnetic eddies can be generated on surfaces. They managed to build a data bit out of only 15 atoms. By way of comparison, a magnetic bit on a common hard drive requires about one million atoms. Yet, writing, updating and reading out information remained a problem. So far, Pfleiderer’s team has resorted to neutron radiation from the neighbouring research reactor FRM II at the TU Muenchen to study the materials. “We can just take the crystals generated in our laboratory at the physics department, walk over there and use the neutrons to measure the magnetic structure, its dynamics and many other properties,” said Pfleiderer.

Using neutron radiation, the scientists were able to prove that even the tiniest of currents are sufficient to move the magnetic eddies. Now the physicists have developed a method by which skyrmions can be moved and measured in a purely electronic manner. “When the electric eddies move in a material, they generate an electric field”, said Pfleiderer. “And that is something we can measure directly with electronic equipment available in our laboratory.”

At present a current is used in the read/write head of a hard drive to generate a magnetic field in order to magnetise a spot on the hard drive and thus write a data bit. Skyrmions, in contrast, can be moved directly – and that with very small currents. “This should make saving and processing data much more compact and energy-efficient,” said Pfleiderer.; Source: Technische Universitaet Muenchen