In most common ground states, the magnetic moments of atoms in crystals order because of interactions with their neighbours. Magnets or magnetic memories illustrate the “ferromagnetic” couplings at the atomic scale. But what happens when a moment receives contradictory information from its neighbours? For instance, in a triangular geometry, three spins can not be simultaneously anti-parallel to each other and therefore they can not satisfy antiferromagnetic interactions. Magnetism is said to be frustrated. Will this situation lead to a global compromise with spins at 120° from each other or a tendency to isolationism by satisfying pairs of spins? A third route was opened theoretically by Anderson in 1973: the moments would form non magnetic pairs (singlets) and the ground state would be built on the resonance of these singlets between neighbouring bonds. This delocalisation breaks the tendency to isolationism and transforms the system into a “spin liquid”. This concept has been seminal for many theoretical investigations, including high temperature superconductors.
|A new synthetic material Cu3Zn(OH)6Cl2, a close relative of a mineral compound discovered in a Chilean mine in 2004 and based on spin triangles forming a kagome net, could well be the very first realization of this novel state. Using a very sensitive probe of magnetism, muons which are produced by collision in large scale facilities and implanted in the material, we could demonstrate the absence of any magnetic ordering at the atomic length scale and down to a few tens of millikelvin. The long sought confrontation of theory with experiment can start!|
- Quantum magnetism in paratacamite family: Towards an ideal kagome lattice P. Mendels et al. , Physical Review Letters. (17 february 2007) 98 077204 http://link.aps.org/abstract/PRL/v9...
- New candidate emerges for a quantum spin liquid Physics Today (february 2007), p 16
Contact researchers: P. Mendels and F. Bert