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Electric current moves magnetic vortices
While Peter Grünberg and Albert Fert were awarded the Nobel Prize in 2007 for research that led to the significantly faster reading of data, over the past few years, scientists have been concentrating on how magnetic information can be directly written to media using an electric current. So far, the problem with this kind of work has been the need for extremely high currents, whose side effects are nearly impossible to rein in, even in nanostructures.
Professor Christian Pfleiderer and first author Florian Jonietz prepare a sample at the instrument MIRA at the FRM II.
In 2009, Professor Christian Pfleiderer and his team at the Physics Department of the TUM discovered an entirely new magnetic structure in a crystal of manganese silicon – a lattice of magnetic vortices. The experiments in Garching were spurred by the theoretical forecasts of Professor Achim Rosch at the Universität zu Köln and Professor Rembert Duine from the Universiteit Utrecht. They were expecting new results in the field of so-called spintronics, nanoelectronic elements that use not only the electric charge of electrons to process information, but also their magnetic moment, or spin.
Christian Pfleiderer’s team of scientists sent an electric current, almost a million times weaker than in earlier studies, through manganese silicon. Using neutrons from FRM II, they were able to observe a twist in the magnetic vortex lattice, which they initially could not explain. More interesting than the twist was the newly discovered magnetic lattice.
Animation: An electron (black sphere) is flying over a lattice of magnetic vortexes. The forces exerted in the process allow the magnetic structures to be controlled using relatively low currents.
Next, Christian Pfleiderer and his team made further measurements using the instrument MIRA at the neutron source FRM II in an attempt to determine why the lattice twisted when a current was applied. When an electron flies through magnetic vortices, the electron’s spin reacts accordingly (see animation). In this way the electric current exerts a force on the magnetic vortices, which eventually begin to flow.
An electron (black sphere) is flying over a lattice of magnetic vortexes. The forces exerted in the process allow the magnetic structures to be controlled using relatively low currents.
After further measurements, the team of Christian Pfleiderer and Achim Rosch was able to establish that the newly discovered lattice of magnetic vortices displays properties that have been of interest in nanotechnology for quite some time. They are, among other things, relevant to the development of new data storage systems. Notably, the magnetic vortices are both very stable and at the same time very weakly anchored in the material, so that even the weakest of electric currents can lead to movement. This will allow data to be written and processed considerably faster and more efficiently in the future.
F. Jonietz, S. Mühlbauer, C. Pfleiderer, A. Neubauer, W. Münzer, A. Bauer, T. Adams, R. Georgii, P. Böni, R. A. Duine, K. Everschor, M. Garst, A. Rosch, Spin Transfer Torques in MnSi at Ultra-low Current Densities, Science, 330, 6011, 17 December 2010, DOI: 10.1126/science.1195709
Publication about the discovery
S. Mühlbauer, B. Binz, F. Jonietz, C. Pfleiderer, A. Rosch, A. Neubauer, R. Georgii, P. Böni, Skyrmion Lattice in a Chiral Magnet, Science, Vol. 323 no. 5916 pp. 915-919, 13 February 2009 – DOI: 10.1126/science.1166767