Crystals can guide and control light and electricity by creating spatially periodic energy barriers. An electron (or photon) can pass through these barriers only when it has a particular energy, allowing engineers to create switches and other electronic devices. Now, a team of researchers from Japan and India has taken a key step towards using crystals to control waves of magnetic orientation (magnons), with the potential to create magnetic analogues to electronic and optical devices, including memory devices and transistors.
Led by YoshiChika Otani at the RIKEN Advanced Science Institute, Wako, the researchers began by manufacturing tiny disks of ferromagnetic material. The magnetic domains of such disks arrange into vortices, which consist of in-plane circular patterns surrounding a core with out-of-plane magnetization. By applying an alternating current with a particular frequency to such disks, physicists can excite the vortices into a gyrating motion, which they can detect by measuring the voltage across a disk.
Otani and his colleagues found that a current oscillating at 352 megahertz could set the vortex of a single disk into motion. When they brought a second disk near the first one, however, this single resonant frequency split into two: one was lower than the original frequency, and the other was higher. This kind of resonance splitting is characteristic of any pair of interacting oscillators with similar energies, whether it be two molecules that are covalently bonded to each other, or two swinging pendula.
The frequency splitting observed in the researchers’ pair of disks indicated that the magnetic vortices in each were coupled together, even though the current was driving one disk only. The researchers showed through numerical simulation that the lower-frequency resonance corresponded to the two vortices rotating in phase with each other; the higher-frequency resonance corresponded to an out-of-phase rotation. Depending on whether the core polarizations of the two disks were pointing in the same or opposite directions, Otani and colleagues also observed different frequency pairs. This led to four distinct resonant frequencies in all.
The researchers could control the differences among the four resonant frequencies by changing the distance between disks, as well as the disk sizes. By demonstrating controllable pairing between adjacent magnetic vortices, the results point the way to more complex chains, lattices and crystals in which magnons can be finely controlled, says Otani. “Our next target is to engineer a structure in which macroscopic spin waves propagate only along particular crystallographic directions.”
The corresponding author for this highlight is based at the Quantum Nano-Scale Magnetics Team, RIKEN Advanced Science Institute
Sugimoto, S., Fukuma, Y., Kasai, S., Kimura, T., Barman, A. & Otani, Y. Dynamics of coupled vortices in a pair of ferromagnetic disks. Physical Review Letters 106, 197203 (2011).
Only an atom thick: Physicists succeed in measuring mechanical properties of 2D monolayer materials
17.01.2018 | Universität des Saarlandes
Black hole spin cranks-up radio volume
15.01.2018 | National Institutes of Natural Sciences
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
17.01.2018 | Ecology, The Environment and Conservation
17.01.2018 | Physics and Astronomy
17.01.2018 | Awards Funding