MIT boffins demonstrate NEW form of magnetism
A state of magnetism predicted in 1987 has been observed for the first time at MIT, with researchers saying that it might one day find applications in storage and communications technologies.
The “one day” is still quite some way off, however, with the researchers only at the very beginning of observing the properties of what’s called a “quantum spin liquid” (QSL).
The properties of a quantum spin liquid are revealed in the spin properties of atoms in a crystal. Rather than settling into a stable state, as happens in ferromagnetic and antiferromagnetic materials, the “spin moment” in a QSL is constantly changing.
In the familiar compass needle, magnetism comes from the alignment of all spins in the same direction. The second magnetic state, antiferromagnetism, was first proposed in the 1930s. In an antiferromagnetic material, the spin states align in such a way that the overall magnetism is zero, unless energy is applied. This property is exploited in hard drive read heads.
In the new state of magnetism, the magnetic orientation of particles is unable to settle into an ordered state. Instead, they fluctuate constantly, driven by quantum interactions between particles.
QSL only exists in a type of crystal called a kagome lattice. In the material examined in the MIT research, Herbertsmithite (named after its discoverer), copper atoms lie at the corners of triangular structures. Two of the copper atoms are able to align their spins in an “up-down” arrangement – but the third copper atom can’t align with both the others, so it flips between up and down.