(ORDO NEWS) — When disordered magnetic materials are cooled to the right temperature, something interesting happens. The spins of their atoms “freeze” and lock into place in a static manner, exhibiting cooperative behavior that would not normally occur.
Now, for the first time, physicists have seen the opposite. When partially heated, the natural magnetic element neodymium freezes, turning all our expectations upside down.
“The magnetic behavior of neodymium that we observe is actually the opposite of what happens “usually,” said physicist Alexander. Khajetoorians from Radboud University in the Netherlands.
“It’s pretty counterintuitive, like water that turns into an ice cube when heated.”
In an ordinary ferromagnetic material, such as iron, the magnetic spins of the atoms are all oriented in the same direction; that is, their north and south magnetic poles are equally oriented in 3D space.
But in some materials, for example, in some alloys of copper and iron, the spins are completely random. This state is known as spin glass.
You might be thinking, “But neodymium is well known for making great magnets,” and you’re right…but it needs to be mixed with iron to get the spins to line up.
Pure neodymium behaves differently than other magnets; just two years ago, physicists determined that this material could best be described as a self-induced spin glass.
Looks like neodymium is even weirder than we thought.
When you heat a material, the increase in temperature increases the energy in that material. In the case of magnets, this increases the motion of the spins. But the opposite also happens: when you cool a magnet, its rotation slows down.
For spin glasses, the freezing point is the point at which the spin glass behaves like a normal ferromagnet.
Led by physicist Benjamin Verlak of Radboud University, a team of scientists wanted to investigate how neodymium behaves when temperature changes.
Interestingly, they found that raising the temperature of the neodymium from -268 degrees Celsius to -265 degrees Celsius (-450.4 to -445 degrees Fahrenheit) caused the freezing state commonly seen when spin glass is cooled.
When the scientists cooled the neodymium back, the spins again fell into disarray.
It is not clear why this happens, as it is very rare for a natural material to behave in a “wrong” way, as opposed to how all other materials of their kind behave. However, scientists believe that this may be due to a phenomenon called frustration.
This is when the material fails to reach an ordered state, resulting in a disordered ground state, as we observe in spin. glasses.
It’s possible, the researchers say, that neodymium has certain correlations in its spin glass state that depend on temperature. Raising the temperature weakens them, and thus the frustration, allowing the spins to even out.
Further research may uncover the mechanism behind this strange behavior in which order emerges from disorder with the addition of energy; the researchers note that this has implications far beyond physics.
“Such pattern freezing does not normally occur in magnetic material,” the Hajeturians explained.
“If we can eventually model the behavior of these materials, that can also be extrapolated to the behavior of a wide range of other materials.”
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