Magnetics Business & Technology - March/April 2021 - 30

VISIONS

Magnonics Researchers at EPFL Use Magnetic Worms to Engineer Nanoscale
Communication Systems
ministically. Although this characteristic makes materials
especially useful for the design of everyday and hightech devices, it remains poorly understood.
The LMGN team found that, under controlled conditions,
a single electromagnetic wave coupled to an artificial
quasicrystal splits into several spin waves, which then
propagate within the structure. Each of these spin waves
represents a different phase of the original electromagnetic wave, carrying different information.

Magnonics researchers at EPFL in Switzerland have
shown that electromagnetic waves coupled to precisely
engineered structures known as artificial ferromagnetic
quasicrystals allow for more efficient information transmission and processing at the nanoscale. Their research
also represents the first practical demonstration of Conway worms, a theoretical concept for the description of
quasicrystals.
Magnonics is an emerging field of magnetism that is
similar to, but slightly different from, spintronics. While
spintronics makes use of an electron's electric charge
and spin moment properties to encode data, magnonics makes use of the amplitude and phase of spin-wave
signals in magnetic materials.
High-frequency electromagnetic waves are used to transmit and process information in microelectronic devices
such as smartphones. It's already appreciated that these
waves can be compressed using magnetic oscillations
known as spin waves or magnons. This compression
could pave the way for the design of nanoscale, multifunctional microwave devices with a considerably reduced footprint. But first, scientists need to gain a better
understanding of spin waves, or precisely how magnons
behave and propagate in different structures.
In a study conducted by doctoral assistant Sho Watanabe, shown at right, postdoctoral researcher Dr. Vinayak Bhat, and other team members, the scientists from
EPFL's Laboratory of Nanoscale Magnetic Materials and
Magnonics examined how electromagnetic waves propagate, and how they could be manipulated, in precisely
engineered nanostructures known as artificial ferromagnetic quasicrystals. The quasicrystals have a unique
property: their structure is aperiodic, meaning that their
constituent atoms or tailor-made elements do not follow
a regular, repeating pattern but are still arranged deter-

Magnetics Business & Technology * March/April 2021

" It's a very interesting discovery,
because existing informationtransmission methods follow
the same principle, " says Dirk
Grundler, an associate professor
at EPFL's School of Engineering. " Except you need an extra
device, a multiplexer, to split the
input signal because, unlike in
our study, it doesn't divide on its
own. "
Dirk Grundler, Associ-

Grundler also explains that, in
ate Professor at EPFL's
conventional systems, the inforSchool of Engineering
mation contained in each wave
can only be read at different frequencies - another inconvenience
that the EPFL team overcame in their study. " In our
two-dimensional quasicrystals, all the waves can be read
at the same frequency, " he adds. The findings have been
published in the journal, Advanced Functional Materials.
The researchers also observed that, rather than propagating randomly, the waves often moved like so-called
Conway worms, named after a well-known mathematician John Horton Conway who also developed a model to
describe the behavior and feeding patterns of prehistoric
worms. Conway discovered that, within two-dimensional
quasicrystals, constituent elements arrange like meandering worms following a Fibonacci sequence. Thereby
they form selected one-dimensional quasicrystals. " Our
study represents the first practical demonstration of this
theoretical concept, proving that the sequences induce
interesting functional properties of waves in a quasicrystal, " says Grundler.
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Magnetics Business & Technology - March/April 2021

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