Experimental physicists are redefining superfast and coherent magnetism

The electronic properties of materials can be directly influenced by absorbing light in less than a femtosecond (10-15 seconds), which is considered the limit of the maximum achievable speed of electronic circuits. On the other hand, the magnetic moment of matter could only be influenced so far by a process related to light and magnetism and by a circuitous route by means of magnetic fields, which is why magnetic switching takes a lot more time and at least several hundred femtoseconds. A consortium of researchers from the Max Planck Institutes for Quantum Optics and Microstructural Physics, the Max Born Institute, the University of Greifswald and the Graz University of Technology have only just been able to manipulate the magnetic properties of a ferromagnetic material both scales the electric field oscillations of visible light – and therefore in sync with the electrical properties – by means of laser pulses. This influence could be accelerated by a factor of 200 and was measured and represented by time-resolved attosecond spectroscopy. The researchers described their experience in the journal Nature.

Material composition as a crucial criterion

In attosecond spectroscopy, magnetic materials are bombarded with ultra-short laser pulses and influenced electronically. “The flashes of light trigger an intrinsic and generally retarding process in the material. The electronic excitation results in a modification of the magnetic properties”, explains Martin Schultze, who until recently worked at the Max Planck Institute for Quantum Optics in Munich, but who is now a professor at the Institute for Experimental Physics at TU Graz. Due to the combination of a ferromagnetic with a non-magnetic metal, the magnetic reaction in the described experiment is however as fast as the electronic reaction. “Thanks to the special constellation, we were able to optically cause a spatial redistribution of the charge carrier, which led to a directly related change in the magnetic properties,” explains Markus Münzenberg. Together with his team from Greifswald, he developed and produced the special material systems.

Schultze is enthusiastic about the magnitude of the research success: “Never before has such a fast magnetic phenomenon been observed. Thanks to this, ultrafast magnetism will take on a whole new meaning.” Sangeeta Sharma, a researcher at the Max Born Institute in Berlin, who predicted the underlying process using computer models, is impressed: “We expect a significant development boost for all applications in which magnetism and electron spin plays a role.

First step towards coherent magnetism

Moreover, the researchers show in their measurements that the observed process takes place in a coherent way: this means that the wave nature of the quantum mechanics of the moving charge carriers is preserved. These conditions allow scientists to use individual atoms as carriers of information instead of larger units of material or to influence changing magnetic properties using another specifically delayed laser pulse, thus advancing the technological miniaturization. “As far as new perspectives are concerned, this could lead to fantastic developments similar to those in the field of magnetism, such as electronic coherence in quantum computing,” hopes Schultze, who now leads a working group focused on attosecond physics at the Institute of Experimental Physics.

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Material provided by Graz University of Technology. Note: Content may be edited for style and length.

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