Pro magnon culture shows promise

US researchers achieve major milestone in quantum magnetic current generation. Andrew Masterson reports.

Pro magnon men, from left to right: Joel Miller, Royce Davidson, Hans Malissa, Haoliang Liu and Christoph Boehme.
Pro magnon men, from left to right: Joel Miller, Royce Davidson, Hans Malissa, Haoliang Liu and Christoph Boehme.
Eric V. Campbell

What could be described as a physics super-group has succeeded in setting the stage for the development of a quantum mechanical field called magnonics – overcoming both technological difficulty and the unfortunate tendency of some of the materials needed to burst into flame.

The super-group luminaries include University of Utah chemist Joel Miller, who in 1991 developed the very first carbon-based magnet that was stable at room temperature.

He is joined by physicists Christoph Boehme and Valy Vardeny who in 2016 showed that quantum waves could be converted into electrical current.

Recently, Miller, Boehme and Vardeny joined forces and together with 11 other colleagues have now revealed that a carbon-based magnet can carry waves of quantum mechanical magnetisation – units known as magnons – and convert them into electrical signals.

The development and use of magnons is known, logically enough, as magnonics. Until now, its applications – in the lab, let alone the wider world – have been severely restricted. This is because researchers have had to rely on an inorganic crystal, yttrium iron garnet (YIG), as the wave carrier.

YIG is very difficult and expensive to produce, thus limiting its use.

Miller, Boehme and Vardeny decided to see if an organic magnet (that is, one containing carbon, not one grown in a pesticide-free field) could carry magnons. To do so, they used electron spin resonance spectroscopy, a method for studying how a magnetic field affects electrons in a material.

The researchers found the magnet was very well suited to the role. However, it had one serious drawback – it was made of a compound called vanadium tetracyanoethylene, a substance known to be rather twitchy.

“If it’s freshly made, it’ll likely catch fire,” Miller says. “It’ll lose its magnetism.”

To overcome this problem, the team made thin films of vanadium tetracyanoethylene and worked with them only in low-oxygen conditions. This meant that test runs would often last for as long as three days continuously, with researchers working in shifts.

The results, however, are very promising. The paper, published in the journal Nature Materials, describes organic magnets able to generate stable magnons and the successful conversion of their spin states into electrical signals.

Although there is still a very long way to go, the aim is to construct a system wherein magnonics can replace electronics. This is important, Boehme says, because magnonics systems can operate with 1000 times less energy than electronics.

Whether that will be feasible, or whether the physics super-group will turn out to be a one-hit wonder, remains to be seen.

“We can’t anticipate,” Miller says, “what we can’t anticipate.”

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