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).
NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center
Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses