Scientists discover new form of magnetism

MIT physicists grew this pure crystal of herbertsmithite in their laboratory. This sample, which took 10 months to grow, is 7mm long and weighs 0.2 grams. Image: Tianheng Han

Researchers at MIT have demonstrated the existence of an entirely new form of magnetism, called quantum spin liquid, only the third type ever to be discovered.

The kind of magnetism most of us are familiar with, ferromagnetism, is what causes compass needles to point north and kids' artworks to stay on fridges.

The second form of magnetism won scientists a Nobel prize just for predicting its existence.

Antiferromagnetism describes a state where opposing magnetic fields of tiny particles within a metal cancel each other out but alter the structure of the metal.

Without that discovery the kind of hard-disks we take for granted in modern computers wouldn't exist.

The new, third form of magnetism has been dubbed quantum spin liquid (QSL) and it behaves very differently indeed.

Within a sparkling, solid crystal that took scientists ten months to create, magnetic "moments" spin and fluctuate constantly, changing their orientation like molecules sliding across one another in a liquid.

This state of flow is something scientists have predicted and aimed to create since the late eighties, but only in recent years did progress accelerate to the point of demonstrating QSL.

So what does this discovery mean for those without a background in theoretical physics?

Well, it's such a fundamental shift in understanding that even the researchers involved can't yet predict the ramifications.

"It may take a long time to translate this very fundamental research into practical applications," said MIT professor of physics Young Lee.

The work could possibly lead to advances in data storage or communications, he said, perhaps using an exotic quantum phenomenon called long-range entanglement, in which two widely separated particles can instantaneously influence each other’s states.

The findings could also bear on research into high-temperature superconductors, which today run MRI machines and mobile phone base stations but could one day enable electric super-trains and smarter power grids.

One of the most fascinating aspects of the exotic, QSL state the scientists created is the way that the magnetism of tiny particles within the crystal influenced one another.

"There is no static order to the magnetic orientations within the material," Lee explained. “But there is a strong interaction between them, and due to quantum effects, they don’t lock in place,” he said.

In quantum terms, these states are bafflingly, neither one thing nor the other.

While most matter has discrete quantum states whose changes are expressed as whole numbers, this QSL material exhibits fractional quantum states.

In fact, the researchers found that these excited states, called spinons, form a continuum, "a remarkable first" for Lee and his colleagues.

"There is no theory that describes everything that we’re seeing," Lee said.

Subir Sachdev, a professor of physics at Harvard University who was not connected with the findings said they were "very significant and open a new chapter in the study of quantum entanglement in many-body systems.”