MIT finds new form of magnetism

Posted by Emma Woollacott

MIT researchers have discovered a completely new type of magnetism, theorized but never before observed.

Ferromagnetism - the simple magnetism of a bar magnet or compass needle - is familiar to every schoolchild; less well-known is antiferromagnetism, the basis for the read heads in today's computer hard disks, in which the magnetic fields of the ions within a metal or alloy cancel each other out. In both cases, the materials become magnetic only when cooled below a certain critical temperature.

But MIT has now shown that there's a third fundamental state for magnetism, known as a quantum spin liquid (QSL): while the QSL is a solid crystal, its magnetic state is described as liquid because the magnetic orientations of the individual particles within it fluctuate constantly.

It was forst ptoposed by theorist Philip Anderson in 1987. "Ever since then, physicists have wanted to make such a state," says MIT professor of physics Young Lee. "It's only in the past few years that we've made progress."

The material itself is a crystal of a mineral called herbertsmithite, first created by the team last year. And, they found, while most matter has discrete quantum states whose changes are expressed as whole numbers, the new QSL material exhibits fractional quantum states.
In fact, the researchers found that these excited states, called spinons, form a continuum: "a remarkable first," they say.

It'll take a long time before the work sees any practical applications, says Lee - although it could lead to advances in data storage or communications. The findings could also bear on research into high-temperature superconductors, and could ultimately lead to new developments in that field, he says.

"We have to get a more comprehensive understanding of the big picture," says Lee. "There is no theory that describes everything that we're seeing."