Scientists From Lancaster University Manipulate Magnets at Atomic Scale

From Lancaster University

Fast and energy-efficient future data processing technologies are on the horizon after an international team of scientists successfully manipulated magnets at the atomic level.

Researchers used ultrashort laser pulse excitation to optically stimulate
specific atomic vibrations of the magnet’s crystal lattice
(Credit Ella Maru Studio and Caviglia Lab, TU Delft)

Dr Rostislav Mikhaylovskiy, physicist, Lancaster University said: “With stalling efficiency trends of current technology, new scientific approaches are especially valuable. Our discovery of the atomically-driven ultrafast control of magnetism opens broad avenues for fast and energy-efficient future data processing technologies essential to keep up with our data hunger.”

Magnetic materials are heavily used in modern life with applications ranging from fridge magnets to Google and Amazon’s data centers used to store digital information.

These materials host trillions of mutually aligned elementary magnetic moments or ‘spins’, whose alignment is largely governed by the arrangement of the atoms in the crystal lattice.

The spin can be seen as an elementary ‘needle of a compass’, typically depicted as an arrow showing the direction from North to South poles. In magnets all spins are aligned along the same direction by the force called exchange interaction. The exchange interaction is one of the strongest quantum effects which is responsible for the very existence of magnetic materials.

The growing demand for efficient magnetic data processing calls for novel means to manipulate the magnetic state and manipulating the exchange interaction would be the most efficient and ultimately fastest way to control magnetism.

To achieve this result, the researchers used the fastest and the strongest stimulus available: ultrashort laser pulse excitation. They used light to optically stimulate specific atomic vibrations of the magnet’s crystal lattice which extensively disturbed and distorted the structure of the material.

The results of this study are published in the journal Nature Materials by the international team from Lancaster, Delft, Nijmegen, Liege and Kiev.

Jorrit Hortensius, PhD student, Technical University of Delft said: “We optically shake the lattice of a magnet that is made up of alternating up and down small magnetic moments and therefore does not have a net magnetization, unlike the familiar fridge magnets.”

After shaking the crystal for a very short period of time, the researchers measured how the magnetic properties evolve directly in time. Following the shaking, the magnetic system of the antiferromagnet changes, such that a net magnetization appears: for a fraction of time the material becomes similar to the everyday fridge magnets.

This all occurs within an unprecedentedly short time of less than a few picoseconds (millionth of a millionth of a second). This time is not only orders of magnitude shorter than the recording time in modern HDDs, but also exactly matches the fundamental limit for the magnetization switching.

Dr Rostislav Mikhaylovskiy, Lancaster University explains: “It has long been thought that the control of magnetism by atomic vibrations is restricted to acoustic excitations (sound waves) and cannot be faster than nanoseconds. We have reduced the magnetic switching time by 1000 times that is a major milestone in itself.”

Dr Dmytro Afanasiev, Technical University of Delft adds: “We believe that our findings will stimulate further research into exploring and understanding the exact mechanisms governing the ultrafast lattice control of the magnetic state.”

Article: Ultrafast control of magnetic interactions via light-driven phonons
Nature Materials has published an article written by D. Afanasiev, J. R. Hortensius, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands, B. A. Ivanov, Institute of Magnetism, National Academy of Sciences and Ministry of Education and Science, Kiev, Ukraine, and National University of Science and Technology MISiS, Moscow, Russian Federation, A. Sasani, E. Bousquet, CESAM QMAT Physique Théorique des Matériaux, Université de Liège, Liège, Belgium, Y. M. Blanter, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands, R. V. Mikhaylovskiy, Department of Physics, Lancaster University, Bailrigg, UK, A. V. Kimel, Institute for Molecules and Materials, Radboud University Nijmegen, Nijmegen, the Netherlands, and A. D. Caviglia, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands .

Abstract: “Resonant ultrafast excitation of infrared-active phonons is a powerful technique with which to control the electronic properties of materials that leads to remarkable phenomena such as the light-induced enhancement of superconductivity, switching of ferroelectric polarization and ultrafast insulator-to-metal transitions. Here, we show that light-driven phonons can be utilized to coherently manipulate macroscopic magnetic states. Intense mid-infrared electric field pulses tuned to resonance with a phonon mode of the archetypical antiferromagnet DyFeO₃ induce ultrafast and long-living changes of the fundamental exchange interaction between rare-earth orbitals and transition metal spins. Non-thermal lattice control of the magnetic exchange, which defines the stability of the macroscopic magnetic state, allows us to perform picosecond coherent switching between competing antiferromagnetic and weakly ferromagnetic spin orders. Our discovery emphasizes the potential of resonant phonon excitation for the manipulation of ferroic order on ultrafast timescales^“.