US scientists predict that magnets can be used as wireless refrigerators in cryogenic applications

Perhaps one day, your home refrigerator can use magnets as "refrigerant." Scientists at the Massachusetts Institute of Technology (MIT) have recently developed equations describing the electron transport in thermoelectrics. They describe the transmission of magnons and find that if they are in a magnetic field that is different, the magnons may move from one end of the magnet to the other. Take away heat and produce cooling effect. Related papers were published in the recent Physical Review Letters.

In a ferromagnet, local magnetic moments can rotate and align in different directions. At absolute zero, the magnetic moment is arranged so that the magnetic force produced by the magnet is the strongest; as the temperature rises, more magnetic moment spins become less synchronous and the magnetic force becomes weaker. The magnon vibrates with this temperature rise. A quasi-magnet is a quasi-particle in a magnet, which is formed by the common rotation of magnetic moments. It is also called "spin".

A magrator is much like electrons. Electrons can carry charges and heat conduction at the same time, and they can move under the influence of electric fields or temperature differences. This phenomenon is the thermoelectric effect. According to the report of the Physicist Organization Network on July 29 (Beijing time), scientists have been studying the thermoelectric effects, such as thermoelectric generators that convert heat directly into electricity, or do not use any moving parts for cooling. The magnon can also move under the action of two forces: temperature difference and magnetic field. The researchers developed the Boltzmann equation for the transmission of electrons in thermoelectrics. Two new equations have been derived to describe the transmission of magnons. They can use new equations to predict the effect of magnon cooling, similar to thermoelectric cooling effects. When the magnon is in a magnetic field with a difference, it carries heat from one end of the magnet to the other.

They built models using ordinary magnetic insulators. From previous data, they collected new data input models for this material and found that when there is a mild magnetic field gradient, it can produce less cooling effect; and at low temperatures, The cooling effect is even more pronounced.

"You can suck heat from one side to the other, and essentially you can use a magnet as a refrigerator," said Liao Bolin, a graduate student of the MIT Mechanical Engineering Department. "You can imagine a kind of wireless cooling. A magnetic magnet a meter or two away, or your laptop can apply a magnetic field to cool it.” According to their theory, this magnetic refrigerator does not require any moving parts, unlike traditional refrigerators. A tube constantly pumps liquid to keep it cool.

Chen Gang, director of the Department of Mechanical Engineering at MIT, believes that the earliest applications for magnon cooling effects may be those that require wireless cooling at very low temperatures. “As far as possible, the possible applications are in cryogenic areas, such as infrared detectors, but we still need to prove this theory through experiments and look for better materials. We hope this will promote new experiments.”

Shi Li, a professor of mechanical engineering at the University of Texas at Austin, said that the magnetic refrigeration effect discovered by the team was "a very useful theoretical framework for studying the combination of spin and heat, and may stimulate some new ideas, such as In a solid-state refrigerator system, a magnon is used as a working 'liquid'."