Terahertz Light-Driven Spin-Lattice Control: New Potential Path to Faster and More Efficient Storage

By University of Cologne

An international team of researchers from the University of Cologne (Germany), Radboud University Nijmegen (The Netherlands), the Ioffe Institute and the Prokhorov General Physics Institute (Russia) has discovered a new mechanism to control spin-lattice interaction using ultrashort terahertz (THz) pulses (terahertz means 10¹² hertz).

This mechanism can open up new and elegant ways to control propagation of spin waves and thus make an important step to conceptually new technologies of data processing in future. The results have been published in Science.

Currently magnetic data recording is dominating data storage technology. It is estimated that soon, more than 7% of the world’s energy production will be spent on data storage centers. Hence there is an urgent demand to develop new technologies to process and store data using ultrafast processes in an energy efficient manner.

Spin-lattice interaction plays a decisive role in magnetic recording processes, where a spin is the elementary magnetic moment of an electron, whose orientation control (up and down) is the base of modern binary computer systems. The scientists used special antiferromagnets in their study—materials in which the ordered spins of electrons align in a regular pattern with neighboring spins pointing in opposite directions. The collective motion of spins in these materials, so-called spin waves, are typically ten times faster than their counterparts in traditional ferromagnetic materials. In contrast to electrons, such spin waves practically do not interact with the crystal lattice and thus can propagate over microscopic distances without losses. In the future spintronics could replace traditional electronics and function as a carrier of information in a magnetic material. This brings the potential for much faster and efficient data processing. At the same time, the weak interaction makes control over propagation of the spin waves challenging. The scientists then ‘drive’ the spin-lattice coupling by applying an ultrashort terahertz pulse.

Dr. Evgeny Mashkovich, senior researcher, Optical Condensed Matter Science group, Institute for Experimental Physics, University of Cologne said: “We showed that we can now control the interaction between lattice and spin waves and, moreover, make it a strong interaction. I believe that this discovery is an important step towards conceptually new technologies for ultra-fast data processing and efficient data storage in the future.”

Article: Terahertz light–driven coupling of antiferromagnetic spins to lattice

Science has published an article written by Evgeny A. Mashkovich, Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, Netherlands, and Institute of Physics II, University of Cologne, D-50937 Cologne, Germany, Kirill A. Grishunin, Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, Netherlands. Roman M. Dubrovin, Ioffe Institute, Russian Academy of Sciences, St. Petersburg 194021, Russia, Anatoly K. Zvezdin, Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow 119991, Russia, and Moscow Institute of Physics and Technology, Dolgoprudnyi 141700, Russia. Roman V. Pisarev, Ioffe Institute, Russian Academy of Sciences, St. Petersburg 194021, Russia, and Alexey V. Kimel, Institute for Molecules and Materials, Radboud University, 6525 AJ Nijmegen, Netherlands.

Abstract: “Understanding spin-lattice coupling represents a key challenge in modern condensed matter physics, with crucial importance and implications for ultrafast and two-dimensional magnetism. The efficiency of angular momentum and energy transfer between spins and the lattice imposes fundamental speed limits on the ability to control spins in spintronics, magnonics, and magnetic data storage. We report on an efficient nonlinear mechanism of spin-lattice coupling driven by terahertz light pulses. A nearly single-cycle terahertz pulse resonantly interacts with a coherent magnonic state in the antiferromagnet cobalt difluoride (CoF₂) and excites the Raman-active terahertz phonon. The results reveal the distinctive functionality of antiferromagnets that allows ultrafast spin-lattice coupling using light.“