The understanding of how spins move and can be manipulated at pico- and femtosecond timescales has implications for ultrafast and energy-efficient data-processing and storage applications. However, the possibility of realizing commercial technologies based on ultrafast spin dynamics has been hampered by our limited knowledge of physics behind processes on this timescale.
An international team of scientists at Ca’ Foscari University of Venice and Stockholm University has- for the first time-observed the ‘nutation’ of these spins in magnetic materials, i.e., the oscillations of their axis during precession.
The measured nutation period was of the order of one picosecond: one-thousandth of a billionth of a second. What’s more, the nutation of the magnetic spin axis is 1000 times faster than precession, a curiously similar ratio to Earth‘s.
According to scientists, this discovery could pave the way toward making digital technologies ever faster, compact, and energetically efficient. To manipulate these phenomena at time scales of thousands of billionths of a second, we first need to know their dynamics, including inertial dynamics.
Stefano Bonetti, who coordinates an ERC project on ultrafast magnetism, said, “This is the first direct and experimental evidence of the inertial movements of magnetic spins, with implications that affect, for example, data centers that store almost all of humanity’s digital information in bits with the north pole up or down, thus encoding the computer 0s and 1s.”
“When these spins are reversed to write information, precession and nutation also come into play. Knowing the nutation period becomes essential as the rotation speed increases. This first observation of these movements paves the way for new technologies to improve the efficiency of our digital activities, which, among all human activities, are recording the highest increase in energy consumption.”
Ca’ Foscari physicist said, “The first experiments were challenging, but, after a couple of years, the machine was already operating at very high performance. These measurements were made over a year, on three different occasions, to check the reproducibility of this never-before observed effect.”
The experiment required collaboration with several European scientific laboratories in Germany (Helmholtz-Zentrum Dresden-Rossendorf, Chemnitz University of Technology, University of Duisburg-Essen, German Aerospace Center (DLR), TU Berlin), France (École Polytechnique), and Italy (Federico II University of Naples and the ‘Parthenope’ University of Naples), with the key measurement made in the Helmholtz Research Centre in Dresden-Rossendorf, German. In this center, the TELBE laboratory can generate intense terahertz radiation (i.e., the frequency range between microwaves and infrared) necessary for the experiment. The group led by Stefano Bonetti was among the first groups to use this laboratory and helped develop the actual machine.
- Kumar Neeraj et al., Inertial spin dynamics in ferromagnets, Nature Physics (2020). DOI: 10.1038/s41567-020-01040-y