Researchers from the Moscow Institute of Physics and Technology and their colleagues from Germany and the Netherlands have achieved material magnetization switching on the shortest timescales, at a minimal energy cost. They have thus developed a prototype of energy-efficient data storage devices. The paper was published in the journal Nature.
The rapid development of information technology calls for data storage devices controlled by quantum mechanisms without energy losses. Maintaining data centers consumes over 3% of the power generated worldwide, and this figure is growing. While writing and reading information is a bottleneck for IT development, the fundamental laws of nature actually do not prohibit the existence of fast and energy-efficient data storage.
The most reliable way of storing data is to encode it as binary zeros and ones, which correspond to the orientations of the microscopic magnets, known as spins, in magnetic materials. This is how a computer hard drive stores information. To switch a bit between its two basic states, it is remagnetized via a magnetic field pulse. However, this operation requires much time and energy.
Back in 2016, Sebastian Baierl from the University of Regensburg in Germany, Anatoly Zvezdin from MIPT in Russia, Alexey Kimel from Radboud University Nijmegen in the Netherlands and Russian Technological University MIREA, along with other colleagues, proposed a way for rapid spin switching in thulium orthoferrite via T-rays. Their technique for remagnetizing memory bits proved faster and more efficient than using magnetic field pulses. This effect stems from a special connection between spin states and the electrical component of a T-ray pulse.
"The idea was to use the previously discovered spin switching mechanism as an instrument for efficiently driving spins out of equilibrium and studying the fundamental limitations on the speed and energy cost of writing information. Our research focused on the so-called fingerprints of the mechanism with the maximum possible speed and minimum energy dissipation," commented study co-author Professor Alexey Kimel of Radboud University Nijmegen and MIREA.
In this study, we exposed spin states to specially tuned T-pulses. Their characteristic photon energies are on the order of the energy barrier between the spin states. The pulses last picoseconds, which corresponds to one light oscillation cycle. The team used a specially developed structure comprised by micrometer-sized gold antennas deposited on a thulium orthoferrite sample.
As a result, the researchers spotted the characteristic spectral signatures indicating successful spin switching with only the minimal energy losses imposed by the fundamental laws of thermodynamics. For the first time, a spin switch was complete in a mere 3 picoseconds and with almost no energy dissipation. This shows the enormous potential of magnetism for addressing the crucial problems in information technology. According to the researchers, their experimental findings agree with theoretical model predictions.
"The rare earth materials, which provided the basis for this discovery, are currently experiencing a sort of a renaissance," said Professor Anatoly Zvezdin, who heads the Magnetic Heterostructures and Spintronics Lab at MIPT. "Their fundamental properties were studied half a century ago, with major contributions by Russian physicists, MSU and MIPT alumni. This is an excellent example of how fundamental research finds its way into practice decades after it was completed."
The joint work of several research teams has led to the creation of a structure that is a promising prototype of future data storage devices. Such devices would be compact and capable of transferring data within picoseconds. Fitting this storage with antennas will make it compatible with on-chip T-ray sources."
Reference: Schlauderer, S., Lange, C., Baierl, S., Ebnet, T., Schmid, C. P., Valovcin, D. C., … Huber, R. (2019). Temporal and spectral fingerprints of ultrafast all-coherent spin switching. Nature, 569(7756), 383. https://doi.org/10.1038/s41586-019-1174-7
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