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posted by martyb on Tuesday January 28 2020, @01:18AM   Printer-friendly
from the 🎜🎝Good-Vibrations🎜🎝 dept.

Detection of very high frequency magnetic resonance could revolutionize electronics:

The finding, reported today in Nature, is based on a magnetic resonance phenomenon in anti-ferromagnetic materials. Such materials, also called antiferromagnets, offer unique advantages for ultrafast and spin-based nanoscale device applications.

The researchers, led by physicist Jing Shi of the University of California, Riverside, generated a spin current, an important physical quantity in spintronics, in an antiferromagnet and were able to detect it electrically. To accomplish this feat, they used terahertz radiation to pump up magnetic resonance in chromia[*] to facilitate its detection.

In ferromagnets, such as a bar magnet, electron spins point in the same direction, up or down, thus providing collective strength to the materials. In antiferromagnets, the atomic arrangement is such that the electron spins cancel each other out, with half of the spins pointing in the opposite direction of the other half, either up or down.

The electron has a built-in spin angular momentum, which can precess the way a spinning top precesses around a vertical axis. When the precession frequency of electrons matches the frequency of electromagnetic waves generated by an external source acting on the electrons, magnetic resonance occurs and is manifested in the form of a greatly enhanced signal that is easier to detect.

In order to generate such magnetic resonance, the team of physicists from UC Riverside and UC Santa Barbara worked with 0.24 terahertz of radiation produced at the Institute for Terahertz Science and Technology's Terahertz Facilities at the Santa Barbara campus. This closely matched the precession frequency of electrons in chromia. The magnetic resonance that followed resulted in the generation of a spin current that the researchers converted into a DC voltage.

[...] Shi, who directs Department of Energy-funded Energy Frontier Research Center Spins and Heat in Nanoscale Electronic Systems, or SHINES, at UC Riverside, explained subterahertz and terahertz radiation are a challenge to detect. Current communication technology uses gigahertz microwaves.

"For higher bandwidth, however, the trend is to move toward terahertz microwaves," Shi said.  "The generation of terahertz microwaves is not difficult, but their detection is. Our work has now provided a new pathway for terahertz detection on a chip."

[...] "Spin dynamics in antiferromagnets occur at a much shorter timescale than in ferromagnets, which offers attractive benefits for potential ultrafast device applications," Shi said.

[...] Shi's team developed a bilayer structure comprised of chromia, an antiferromagnetic insulator, with a layer of metal on top of it to serve as the detector to sense signals from chromia.

Shi explained that electrons in chromia remain local. What crosses the interface is information encoded in the precessing spins of the electrons.

[...] The researchers addressed spin sensitivity by focusing on platinum and tantalum as metal detectors. If the signal from chromia originates in spin, platinum and tantalum register the signal with opposite polarity. If the signal is caused by heating, however, both metals register the signal with identical polarity.

"This is the first successful generation and detection of pure spin currents in antiferromagnetic materials, which is a hot topic in spintronics," Shi said. "Antiferromagnetic spintronics is a major focus of SHINES."

[*] Chromia:

Chromium(III) oxide (or chromia) is an inorganic compound with the formula Cr2O3. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

Journal Reference:
Junxue Li, C. Blake Wilson, Ran Cheng, Mark Lohmann, Marzieh Kavand, Wei Yuan, Mohammed Aldosary, Nikolay Agladze, Peng Wei, Mark S. Sherwin & Jing Shi. Spin current from sub-terahertz-generated antiferromagnetic magnons$, Nature (DOI: doi:10.1038/s41586-020-1950-4)


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  • (Score: 2) by Muad'Dave on Tuesday January 28 2020, @01:23PM (2 children)

    by Muad'Dave (1413) on Tuesday January 28 2020, @01:23PM (#950039)

    I was going to comment on that. Instead of 240 GHz, they chose to call it 0.24 THz so they could get that new buzzword in there.

    Also, THz waves do propagate in air, but are strongly absorbed by atmospheric gases. The effective range in on the order of 10m or so [wikipedia.org]. The TSA scanners these days all utilize THz emissions.

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  • (Score: 2) by takyon on Tuesday January 28 2020, @03:01PM (1 child)

    by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Tuesday January 28 2020, @03:01PM (#950072) Journal

    TFA does mention "subterahertz".

    This is one in a long line of spintronics articles. A lot of hype but not much to show for it... yet. Hopefully we get new transistors or storage devices out of it.

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    • (Score: 1) by DECbot on Tuesday January 28 2020, @04:52PM

      by DECbot (832) on Tuesday January 28 2020, @04:52PM (#950128) Journal

      From TFS, it looks like they are investigating new receivers that are more sensitive to ~1mm wavelengths. These will be the ultimate line-of-sight devices. Even the atmosphere will block the signal if the devices are too far away. Nonetheless, it is pretty cool that they can make an actual electronic use out of antiferromagnets.

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