New research published in Science brings us a step closer to magnonic devices and quantum computing. Neutron analysis has revealed the behaviour of magnetic waves in a class of materials, enabling scientists to picture a future where electronic currents no longer cause our devices to heat up.
Magnetic excitations can behave in a particle-like way that mimics electrons, known as ‘magnons’. Magnons emerge from the spin-waves in certain materials, rippling outwards from a disturbance without transferring any actual matter – like a crowd wave at a football stadium. They can carry information like electrical currents do, but with lower energy.
Today’s electronic devices waste huge amounts of energy. They heat up as the electrons carrying the information meet resistance as they travel through wires. Operators of large datacenters like those for major tech companies spend billions of dollars a year on cooling systems for computers – up to 40% of their energy demand. Scientists around the world are looking to understand how the behaviour of magnetic spin waves could unlock an alternative future for data transfer.
To fully harness this potential, researchers need to control the properties and behaviour of the waves, such as their wavelength or direction. Exciting new research has proved that in a particular magnetic configuration, known as skyrmions, not only are the waves electron-like in behaviour, they closely mimic the motion of electrons in response to a magnetic field. Thus, their movement may be predicted more accurately and exploited for future technologies such as novel information storage and quantum computing.
In order to reveal this novel circular spin-wave motion around skyrmions, representing a major step-change in our understanding of magnons, researchers used the world’s most powerful neutron beams for their experiments. As a fundamental particle with its own magnetic moment, neutron scattering is the only technique that could respond to the magnetic fields – like a compass needle detecting the North Pole. With the largest neutron flux in the world, the crucial experiments were performed at the Institut Laue-Langevin, in Grenoble, France.
In conventional ferromagnetic materials, the moments all point in the same direction, so the magnetic waves generally propagate in a straight line. However, in a relatively new class of materials, the magnetic configuration is quite different and holds immense potential. Manganese silicide (MnSi) is one such material where the magnetic moments form a tight vortex-like arrangement, the skyrmions, which extend along tubes like a box of uncooked spaghetti. MnSi, which was discovered in cosmic dust from a comet, is the archetypal model for studying skyrmions. In this research, the motion of spin-waves around the magnetic ‘tubes’ was observed, and the similarity to electrons in the way that they move in a circular motion perpendicular to the skyrmion established.
Researchers are now one step closer to the revolutionary potential of magnons. Tangible devices or technologies that exploit these phenomena are still far in the future, with limitations still in play such as the immensely low temperatures required to exhibit the behaviour described. Yet, with the growing influence of electronic devices and data storage demands on the planet, solutions to control and implement quantum physics continue to be important to our future.
Tobias Weber, Physicist at Institut Laue-Langevin and the paper’s lead author said:
"There are huge challenges ahead for the application of these fundamental findings in future technologies, yet our observations of the skyrmion dynamics are highly influential on the field. The ThALES instrument at ILL is the only tool with which we could make this discovery, as the most intense spectrometer of its kind in the world. The polarisation of the neutrons also transforms our ability to see the magnons compared to any other technique, making it possible to see exactly which results came from the magnetic contribution.
“The next steps for this journey will surround the mysterious and challenging materials in which we observe the skyrmion structure. Studying magnetic behaviour in MnSi and its counterparts requires extremely low temperatures (-243.15 Celsius), so we are a long way from applying these findings in technologies at room temperatures.”
This research involved an international collaboration between the Institut Laue-Langevin in France, the Swiss spallation source SINQ at the Paul Scherrer Institute, the UK’s ISIS neutron and muon source, the U.S. Los Alamos National Laboratory, the Karlsruhe Institute of Technology and the Research Neutron Source Heim Maier-Leibnitz (FRM II) at the Technical University of Munich (TUM).
ThALES, the three axis low energy spectrometer at ILL was used for this research. It is used to measure magnetic excitations due to its world-leading high neutron flux and the possibility to experiment with extreme sample environments. You can find out more about it here: https://www.ill.eu/users/instruments/instruments-list/thales/description/instrument-layout