Frustrated Magnets and Their Vexed Behaviors: The Hall Effect

Frustrated magnets are discontented quantum materials and now, scientists have learned a bit more about them. A new experiment reveals an unlikely behavior in this class of materials, addressing a long-debated question about their nature.

In this latest study, the researchers tested frustrated magnets to see if they had a behavior called the Hall Effect. When a magnetic field is applied to an electric current flowing in a conductor such as a copper ribbon, the current deflects to one side of the ribbon. This deflection, first observed in 1879, is used in sensors for devices such as computer printers and automobile anti-lock braking systems.

Because the Hall Effect occurs in charge-carrying particles, most physicists thought it would be impossible to see such behavior in non-charged, or neutral, particles like those in frustrated magnets. Others, though, speculated that the neutral particles in frustrated magnets might behind in the Hall rule under extremely cold conditions, near absolute zero, where particles behave according to the laws of quantum mechanics rather than the classical physical laws.

The researchers first turned to a class of the magnets called pyrochlores. These contain magnetic moments that, at very low temperatures near absolute zero, should line up in an orderly manner so that all of their "spins" point in the same direction. Yet the scientists found in experiments that instead the spins pointed in random directions.

That's why researchers decided to measure the Hall Effect at an extremely low temperature where the quantum nature of the materials comes out. The researchers first synthesized materials and then tested them.

"All of us were very surprised because we work and play in the classical, non-quantum world," said Phuan Ong, one of the researchers, in a news release. "Quantum behavior can seem very strange, and this one example where something that shouldn't happen is really there. It really exists."

It turns out that these materials do exhibit the Hall Effect. This may be important to note for the future of the electronics industry.

The findings are published in the journal Science.

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