Featured Research

from universities, journals, and other organizations

New meaning to refrigerator magnets: Magnets may act as wireless cooling agents

Date:
July 28, 2014
Source:
Massachusetts Institute of Technology
Summary:
The magnets cluttering the face of your refrigerator may one day be used as cooling agents, according to a new theory. A magnetically driven refrigerator would require no moving parts, unlike conventional iceboxes that pump fluid through a set of pipes to keep things cool.

A new theory predicts magnets may act as wireless cooling agents.
Credit: llustration: Jose-Luis Olivares/MIT

The magnets cluttering the face of your refrigerator may one day be used as cooling agents, according to a new theory formulated by MIT researchers.

Related Articles


The theory describes the motion of magnons -- quasi-particles in magnets that are collective rotations of magnetic moments, or "spins." In addition to the magnetic moments, magnons also conduct heat; from their equations, the MIT researchers found that when exposed to a magnetic field gradient, magnons may be driven to move from one end of a magnet to another, carrying heat with them and producing a cooling effect.

"You can pump heat from one side to the other, so you can essentially use a magnet as a refrigerator," says Bolin Liao, a graduate student in MIT's Department of Mechanical Engineering. "You can envision wireless cooling where you apply a magnetic field to a magnet one or two meters away to, say, cool your laptop."

In theory, Liao says, such a magnetically driven refrigerator would require no moving parts, unlike conventional iceboxes that pump fluid through a set of pipes to keep things cool.

Liao, along with graduate student Jiawei Zhou and Department of Mechanical Engineering head Gang Chen, have published a paper detailing the magnon cooling theory in Physical Review Letters.

"People now have a new theoretical playground to study how magnons move under coexisting field and temperature gradients," Liao says. "These equations are pretty fundamental for magnon transport."

A cool effect

In a ferromagnet, the local magnetic moments can rotate and align in various directions. At a temperature of absolute zero, the local magnetic moments align to produce the strongest possible magnetic force in a magnet. As temperature increases, a magnet becomes weaker as more local magnetic moments spin away from the shared alignment; a magnon population is created with this elevated temperature.

In many ways, magnons are similar to electrons, which can simultaneously carry electrical charge and conduct heat. Electrons move in response to either an electric field or a temperature gradient -- a phenomenon known as the thermoelectric effect. In recent years, scientists have investigated this effect for applications such as thermoelectric generators, which can be used to convert heat directly into electricity, or to deliver cooling without any moving parts.

Liao and his colleagues recognized a similar "coupled" phenomenon in magnons, which move in response to two forces: a temperature gradient or a magnetic field. Because magnons behave much like electrons in this aspect, the researchers developed a theory of magnon transport based on a widely established equation for electron transport in thermoelectrics, called the Boltzmann transport equation.

From their derivations, Liao, Zhou, and Chen came up with two new equations to describe magnon transport. With these equations, they predicted a new magnon cooling effect, similar to the thermoelectric cooling effect, in which magnons, when exposed to a magnetic field gradient, may carry heat from one end of a magnet to the other.

Motivating new experiments

Liao used the properties of a common magnetic insulator to model how this magnon cooling effect may work in existing magnetic materials. He collected data for this material from previous literature, and plugged the numbers into the group's new model. He found that while the effect was small, the material was able to generate a cooling effect in response to a moderate magnetic field gradient. The effect was more pronounced at cryogenic temperatures.

The theoretical results suggest to Chen that a first application for magnon cooling may be for scientists working on projects that require wireless cooling at extremely low temperatures.

"At this stage, potential applications are in cryogenics -- for example, cooling infrared detectors," Chen says. "However, we need to confirm the effect experimentally and look for better materials. We hope this will motivate new experiments."

Li Shi, a professor of mechanical engineering at the University of Texas at Austin who was not involved in the research, says the magnetic cooling effect identified by the group is "a highly useful theoretical framework for studying the coupling between spin and heat, and can potentially stimulate ideas of utilizing magnons as a working 'fluid' in a solid-state refrigeration system."

Liao points out that magnons also add to the arsenal of tools for improving existing thermoelectric generators -- which, while potentially innovative in their ability to generate electricity from heat, are also relatively inefficient.

"There's still a long way to go for thermoelectrics to compete with traditional technologies," Liao says. "Studying the magnetic degree of freedom could potentially help optimize existing systems and improve the thermoelectric efficiency."

The work was partly supported by the U.S. Department of Energy and the Air Force Office of Scientific Research.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Jennifer Chu. Note: Materials may be edited for content and length.


Journal Reference:

  1. Bolin Liao, Jiawei Zhou, Gang Chen. Generalized Two-Temperature Model for Coupled Phonon-Magnon Diffusion. Physical Review Letters, 2014; 113 (2) DOI: 10.1103/PhysRevLett.113.025902

Cite This Page:

Massachusetts Institute of Technology. "New meaning to refrigerator magnets: Magnets may act as wireless cooling agents." ScienceDaily. ScienceDaily, 28 July 2014. <www.sciencedaily.com/releases/2014/07/140728104714.htm>.
Massachusetts Institute of Technology. (2014, July 28). New meaning to refrigerator magnets: Magnets may act as wireless cooling agents. ScienceDaily. Retrieved December 22, 2014 from www.sciencedaily.com/releases/2014/07/140728104714.htm
Massachusetts Institute of Technology. "New meaning to refrigerator magnets: Magnets may act as wireless cooling agents." ScienceDaily. www.sciencedaily.com/releases/2014/07/140728104714.htm (accessed December 22, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Monday, December 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Touch-Free Smart Phone Empowers Mobility-Impaired

Touch-Free Smart Phone Empowers Mobility-Impaired

Reuters - Innovations Video Online (Dec. 21, 2014) A touch-free phone developed in Israel enables the mobility-impaired to operate smart phones with just a movement of the head. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Building Google Into Cars

Building Google Into Cars

Reuters - Business Video Online (Dec. 19, 2014) Google's next Android version could become the standard that'll power your vehicle's entertainment and navigation features, Reuters has learned. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
AP Review: Nikon D750 and GoPro Hero 4

AP Review: Nikon D750 and GoPro Hero 4

AP (Dec. 19, 2014) What to buy an experienced photographer or video shooter? There is some strong gear on the market from Nikon and GoPro. The AP's Ron Harris takes a closer look. (Dec. 19) Video provided by AP
Powered by NewsLook.com
Obama: Better Ways to Create Jobs Than Keystone Pipeline

Obama: Better Ways to Create Jobs Than Keystone Pipeline

AFP (Dec. 19, 2014) US President Barack Obama says that construction of the Keystone pipeline would have 'very little impact' on US gas prices and believes there are 'more direct ways' to create construction jobs. Duration: 00:47 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins