R&D: Physicists Create Prototype Superefficient Memory for Future Computers

From Moscow Institute of Physics and Technology (MIPT),
and from Universität Regensburg (see below)

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, University of Regensburg, Germany, Anatoly Zvezdin, MIPT, Russia, Alexey Kimel, Radboud University Nijmegen, 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 Alexey Kimel, study co-author professor, 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 three 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, 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.

From Universität Regensburg

International team of scientists demonstrates superfast optical magnetization switching with record efficiency

Using ultrashort pulses of light enables extremely economical switching of spins
within a few picoseconds from one stable orientation (red arrow) to another (white arrow).
(Illustration: Brad Baxley, parttowhole.com)

Using extremely short bursts of light, precisely shaped in a custom-cut gold antenna, an international research team from Germany, The Netherlands, Russia, and the US has switched the magnetization state of a solid faster and more efficiently than ever before. Their key achievement could pave the way towards a novel kind of nearly dissipation-free information technology. The results are published in the current issue of the top-tier journal Nature.

Modern electronics has to be ever faster and more compact. Yet this challenge comes with a fundamental predicament: Performing a task more rapidly costs more energy. State-of-the-art technology allows for reading and writing information on a hard disk drive at a rate of up to one billion (109) bits per second. The binary information (0 or 1, respectively) is encoded in the orientation of tiny magnetic moments called spins. A magnetic read/write head is used to set or retrieve the information. While this scheme has defined large-scale magnetic data storage for more than six decades, it is facing fundamental limitations regarding energy efficiency and speed. Already now, data centers around the world are responsible for 5% of the world’s electricity consumption – a staggering and continuously increasing figure. In light of this, it may sound like a dream that the laws of physics do not prohibit ultrafast and almost dissipation-free information processing.

Researchers around Dr. Christoph Lange and Prof. Dr. Rupert Huber (Department of Physics, University of Regensburg) as well as Dr. Rostislav Mikhaylovskiy, Prof. Dr. Alexey Kimel (Radboud University, Nijmegen, The Netherlands) and Prof. Dr. Anatoly Zvezdin (Institute of the Russian Academy of Sciences, Moscow, Russia) have now made a large leap towards ultrafast information storage with minimal energy dissipation. In principle, low-energy electromagnetic pulses in the far infrared – the so-called terahertz spectral range – should allow for steering spins from one stable configuration to another to encode information in the shortest possible time, and at the minimal possible expense of energy. So far, however, even the strongest sources of terahertz radiation did not provide sufficiently strong fields to achieve this goal. “It has been possible for a few years to wobble spins around a little bit, but pushing them hard enough to fully reverse their orientation had remained impossible”, as Stefan Schlauderer, PhD student, and first author of the study, explains.

The international consortium cut the Gordian knot by combining the expertise of the Nijmegen group on a material class called antiferromagnets with the ability of the Regensburg group to control solids with the help of custom-tailored terahertz electromagnetic waveforms faster than even a single oscillation cycle of light. The international team utilized a novel interaction mechanism which efficiently couples the spin motion to terahertz electric fields. In order to reach sufficient field strengths they used a trick from cutting-edge nanooptics. They developed and fabricated a very small antenna which strongly concentrates and thus enhances the terahertz radiation. With this structure, the force on the spins exerted by the terahertz pulses was strong enough to change the structure’s magnetic orientation within just a few picoseconds (millionths of a millionths of a second) while requiring only a single quantum – a photon – of the terahertz light field, per spin.

Their scheme not only surpasses the speed of existing technologies by a factor of more than 1000, it furthermore sets a new record in terms of energy efficiency.

“The amount of energy put into the switching process is spot-on, which allows for virtually frictionless spin motion. Our approach thus bears potential for quantum information processing,” Dr. Lange details.

The results are a key step towards a new generation of information technology which aims to simultaneously enable maximal energy efficiency and speed.

Article: Temporal and spectral fingerprints of ultrafast all-coherent spin switching

Nature has published an article written by S. Schlauderer, C. Lange, S. Baierl, T. Ebnet, C. P. Schmid, Department of Physics, University of Regensburg, Regensburg, Germany, D. C. Valovcin, Department of Physics and the Institute for Terahertz Science and Technology, and University of California at Santa Barbara, Santa Barbara, CA, USA, A. K. Zvezdin, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia, P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia, and Magnetic Heterostructures and Spintronics Laboratory, Moscow Institute of Physics and Technology (State University), Dolgoprudny, Russia, A. V. Kimel, Laboratory for Ultrafast Dynamics in Ferroics, Russian Technological University (MIREA), Moscow, Russia, and Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands, R. V. Mikhaylovskiy, Institute for Molecules and Materials, Radboud University, Nijmegen, The Netherlands, and present address: Department of Physics, Lancaster University, Bailrigg, UK, and R. Huber, Department of Physics, University of Regensburg, Regensburg, German.

Abstract: “Future information technology demands ever-faster, low-loss quantum control. Intense light fields have facilitated milestones along this way, including the induction of novel states of matter, ballistic acceleration of electrons and coherent flipping of the valley pseudospin. These dynamics leave unique ‘fingerprints’, such as characteristic bandgaps or high-order harmonic radiation. The fastest and least dissipative way of switching the technologically most important quantum attribute—the spin—between two states separated by a potential barrier is to trigger an all-coherent precession. Experimental and theoretical studies with picosecond electric and magnetic fields have suggested this possibility, yet observing the actual spin dynamics has remained out of reach. Here we show that terahertz electromagnetic pulses allow coherent steering of spins over a potential barrier, and we report the corresponding temporal and spectral fingerprints. This goal is achieved by coupling spins in antiferromagnetic TmFeO₃ (thulium orthoferrite) with the locally enhanced terahertz electric field of custom-tailored antennas. Within their duration of one picosecond, the intense terahertz pulses abruptly change the magnetic anisotropy and trigger a large-amplitude ballistic spin motion. A characteristic phase flip, an asymmetric splitting of the collective spin resonance and a long-lived offset of the Faraday signal are hallmarks of coherent spin switching into adjacent potential minima, in agreement with numerical simulations. The switchable states can be selected by an external magnetic bias. The low dissipation and the antenna’s subwavelength spatial definition could facilitate scalable spin devices operating at terahertz rates.“