When disordered magnetic materials are refrigerated to just the right temperature, something intriguing happens. The spins of their atoms ‘freeze’ and lock into place in a static pattern, displaying a cooperative behavior that is not usually seen.
However, for the first time, physicists have detected the opposite. When fractionally heated, the typically occurring magnetic element neodymium freezes.
“The magnetic behavior in neodymium that we observed is actually the opposite of what ‘normally’ happens,” announced physicist Alexander Khajetoorians of Radboud University in the Netherlands.
“It’s quite counterintuitive, like water that becomes an ice cube when it’s heated up.”
In a usual ferromagnetic material, like iron, the magnetic spins of the atoms all align in the same direction; that is, their north and south magnetic poles face the same way in three-dimensional space.
However, in some materials, like some alloys of copper and iron, the spins are relatively random. This state is what we call the spin glass.
We still don’t know why this occurs since it’s very unusual that a natural material behaves in the ‘wrong’ way, pared to how all the other materials of its kind behave. The scientists, however, believe that it may have something to do with a phenomenon called frustration.
This is when a material is incapable of attaining an ordered state, resulting in a disordered ground state, as we notice in spin glasses.