MIT researchers discover a new kind of magnetism
By By David L. Chandler, MIT News Office | 20 Dec 2012
Following up on earlier theoretical predictions, MIT researchers have now demonstrated experimentally the existence of a fundamentally new kind of magnetic behaviour, adding to the two previously known states of magnetism.
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| MIT physicists grew this pure crystal of herbertsmithite in their laboratory. This sample, which took 10 months to grow, is 7 mm long (just over a quarter-inch) and weighs 0.2 grams. Image: Tianheng Han |
Ferromagnetism - the simple magnetism of a bar magnet or compass needle - has been known for centuries. In a second type of magnetism, anti-ferromagnetism, 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.
The prediction and discovery of anti-ferromagnetism - the basis for the read heads in today's computer hard disks - won Nobel Prizes in physics for Louis Neel in 1970 and for MIT professor emeritus Clifford Shull in 1994.
''We're showing that there is a third fundamental state for magnetism,'' says MIT professor of physics Young Lee. The experimental work showing the existence of this new state, called a quantum spin liquid (QSL), is reported this week in the journal Nature, with Lee as the senior author and Tianheng Han, who earned his PhD in physics at MIT earlier this year, as lead author.
The QSL is a solid crystal, but its magnetic state is described as liquid: Unlike the other two kinds of magnetism, the magnetic orientations of the individual particles within it fluctuate constantly, resembling the constant motion of molecules within a true liquid.
Finding the evidence
There is no static order to the magnetic orientations, known as magnetic moments, within the material, Lee explains. ''But there is a strong interaction between them, and due to quantum effects, they don't lock in place,'' he says.
