Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Turning back time by controlling magnetic interactions

30.03.2015

In a publication in Nature Communications, researchers at the Max Planck Institute for the Structure and Dynamics of Matter laid the theoretical foundation for more efficient magnetic storage.

In many materials, macroscopic magnetic properties emerge when microscopically small magnets align in a fixed pattern throughout the whole solid. In a publication in Nature Communications, Johan Mentink, Karsten Balzer and Martin Eckstein from the University of Hamburg at the Center for Free-Electron Laser Science (CFEL) and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) have predicted that the interactions causing this alignment can be changed almost instantaneously and reversibly under the influence of a laser pulse. In future, this effect may be used for the development of faster magnetic storage. Besides this, the finding implies the highly counter-intuitive consequence that the magnetic dynamics can effectively run backwards in time under the influence of a sufficiently strong time-periodic laser field.


Illustration of time reversal: under the influence of a periodic electric field from a laser (yellow), the evolution of the spins (red) goes backward in time.

Graphics: J.M. Harms, MPSD

The strongest interactions in magnetic materials are called exchange interactions since they are caused by the exchange of electrons between individual microscopic magnets, called spins. A spin can feel a force from its neighbor that is up to a hundred times larger than the magnetic fields available in the laboratory. Johan Mentink and collaborators have shown that the electric field of the laser can influence the electrons during this exchange process and thus modify the interaction. Owing to the strength of the exchange interactions, this holds the promise to achieve a control of magnetism on the fastest possible timescale, with high relevance for technological applications such as magnetic storage.

While it has been demonstrated before that exchange interactions can be modified very rapidly, the ultimate control of exchange interactions would be achieved when one can selectively strengthen or weaken the interactions when the electric field is turned on and off, for example. This has now been demonstrated by exposing the magnetic material to a time-periodic electric field that is deliberately tuned to avoid a direct excitation of the electrons. Interestingly, even for the model system considered, this protocol already displays a rich control: the exchange interaction can be enhanced, weakened, and even reverse sign, thus favoring parallel instead of anti-parallel alignment of neighboring spins.

Quite surprisingly, upon changing the sign of the exchange interaction by the periodic electric laser field, it was observed that the spin dynamics turns back time. Mentink: ‘This demonstration caused a lot of excitement during our studies. Intuitively, one expects that a sign change of the interaction causes a rapid change of the magnetic state, but we find instead that the spins evolve back to their original orientation without any signature of a different magnetic state’. As a result, our studies do not only have high relevance for technological applications, but also for fundamental studies on the time-reversibility of quantum systems.

Contact persons:

Prof. Dr. Martin Eckstein
Max-Planck-Institut für Struktur und Dynamik der Materie
Luruper Chaussee 149
22761 Hamburg / Germany
Tel.:+49 (0)40 8998-6270
Email: martin.eckstein@mpsd.cfel.de

Dr. Johan Mentink
Radboud University
Institute for Molecules and Materials
Heyendaalseweg 135
6525 AJ Nijmegen / The Netherlands
Tel.: +31 (0)24 3652903
Email: j.mentink@science.ru.nl

Original publication:
Johan. H. Mentink, Karsten Balzer, and Martin Eckstein, "Ultrafast and reversible control of the exchange interaction in Mott insulators”, Nature Communications, 2015, DOI: 10.1038/ncomms7708

Weitere Informationen:

http://dx.doi.org/10.1038/ncomms7708 Original publication
http://www.mpsd.mpg.de/en/research/cmd/theo Research group of Prof. Dr. Martin Eckstein
http://www.mpsd.mpg.de/en Max Planck Institute for the Structure and Dynamics of Matter

Dr. Joerg Harms | Max-Planck-Institut für Struktur und Dynamik der Materie

More articles from Physics and Astronomy:

nachricht What happens when we heat the atomic lattice of a magnet all of a sudden?
17.07.2018 | Forschungsverbund Berlin

nachricht Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Microscopic trampoline may help create networks of quantum computers

17.07.2018 | Information Technology

In borophene, boundaries are no barrier

17.07.2018 | Materials Sciences

The role of Sodium for the Enhancement of Solar Cells

17.07.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>