Researchers find that magnets can control heat and sound

Researchers
at The Ohio State University have discovered how to control heat with a
magnetic field. In the March 23 issue of the journal Nature Materials, they
describe how a magnetic field roughly the size of a medical MRI reduced the
amount of heat flowing through a semiconductor by 12 percent.

The
study is the first ever to prove that acoustic phonons—the elemental particles
that transmit both heat and sound—have magnetic properties. “This adds a
new dimension to our understanding of acoustic waves,” said Joseph
Heremans, Ohio Eminent Scholar in Nanotechnology and professor of mechanical
engineering at Ohio State. “We’ve shown that we can steer heat
magnetically. With a strong enough magnetic field, we should be able to steer
sound waves, too.”

Researchers
at The Ohio State University have discovered that heat can be controlled with a
magnetic field. Here, study leader Joseph Heremans, Ohio Eminent Scholar in
Nanotechnology, holds the material used in the experiment: a piece of indium
antimonide semiconductor shaped into a lopsided tuning fork. The wider arm of
the fork (left) measures 4 mm wide, and the narrower one (right) measures 1 mm.
The researchers were able to slow the movement of heat through the wider arm of
the fork using a magnetic field. Credit: Photo by Kevin Fitzsimons, courtesy of
The Ohio State University.

People
might be surprised enough to learn that heat and sound have anything to do with
each other, much less that either can be controlled by magnets, Heremans
acknowledged. But both are expressions of the same form of energy, quantum
mechanically speaking. So any force that controls one should control the other.
“Essentially, heat is the vibration of atoms,” he explained.
“Heat is conducted through materials by vibrations. The hotter a material
is, the faster the atoms vibrate.

“Sound
is the vibration of atoms, too,” he continued. “It’s through vibrations
that I talk to you, because my vocal chords compress the air and create
vibrations that travel to you, and you pick them up in your ears as
sound.” The name “phonon” sounds a lot like “photon.”
That’s because researchers consider them to be cousins: Photons are particles
of light, and phonons are particles of heat and sound. But researchers have
studied photons intensely for a hundred years—ever since Einstein discovered
the photoelectric effect. Phonons haven’t received as much attention, and so not
as much is known about them beyond their properties of heat and sound.

This
study shows that phonons have magnetic properties, too.

“We
believe that these general properties are present in any solid,” said
Hyungyu Jin, Ohio State postdoctoral researcher and lead author of the study. The
phonons reacted to the magnetic field, so the particles must be sensitive to
magnetism, the researchers concluded. Next, they plan to test whether they can
deflect sound waves sideways with magnetic fields. (Source: Nature
Materials/The Ohio State University).

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