Subscribe free to our newsletters via your
. 24/7 Space News .




TIME AND SPACE
Refrigerator magnets
by Jennifer Chu
Boston MA (SPX) Jul 29, 2014


Image courtesy Jose-Luis Olivares and 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. 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.

.


Related Links
Massachusetts Institute of Technology
Understanding Time and Space






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TIME AND SPACE
Is The Universe A Bubble? Let's Check
Waterloo, Canada (SPX) Jul 23, 2014
Never mind the big bang; in the beginning was the vacuum. The vacuum simmered with energy (variously called dark energy, vacuum energy, the inflation field, or the Higgs field). Like water in a pot, this high energy began to evaporate - bubbles formed. Each bubble contained another vacuum, whose energy was lower, but still not nothing. This energy drove the bubbles to expand. Inevitably, s ... read more


TIME AND SPACE
China's biggest moon challenge: returning to earth

Lunar Pits Could Shelter Astronauts, Reveal Details of How 'Man in the Moon' Formed

Manned mission to Moon scheduled by Roscosmos for 2020-2031

Landsat Looks to the Moon

TIME AND SPACE
NASA Seeks Proposals for Commercial Mars Data Relay Satellites

Emirates paves way for Middle East space program with mission to Mars

Curiosity's images show Earth-like soils on Mars

India could return to Mars as early as 2017

TIME AND SPACE
Sierra Nevada Completes Major Dream Chaser NASA CCiCap Milestone

NASA Partners Punctuate Summer with Spacecraft Development Advances

Voyager Spacecraft Might Not Have Reached Interstellar Space

New Fort Knox: A means to a solar-system-wide economy

TIME AND SPACE
China to launch HD observation satellite this year

Lunar rock collisions behind Yutu damage

China's Fast Track To Circumlunar Mission

Chinese moon rover designer shooting for Mars

TIME AND SPACE
Russian Cargo Craft Launches for 6-Hour Trek to ISS

ISS Crew Opens Cargo Ship Hatch, Preps for CubeSat Deployment

Russian cargo craft docks with ISS, science satellite fails

ATV-5: loaded and locked

TIME AND SPACE
China to launch satellite for Venezuela

SpaceX Soft Lands Falcon 9 Rocket First Stage

SpaceX Falcon 9 v1.1 Flights Deemed Successful

ISS 'space truck' launch postponed: Arianespace

TIME AND SPACE
'Challenges' in quest to find water on Earth-like worlds: study

Transiting Exoplanet with Longest Known Year

Brown Dwarfs May Wreak Havoc on Orbits of Nearby Planets

NASA Mission To Reap Bonanza of Earth-sized Planets

TIME AND SPACE
Laser experiment reveals liquid-like motion of atoms in an ultra-cold cluster

Amazon launches 3D printing store

Carbyne morphs when stretched

Diode laser strong enough to cut metal developed by former MIT scientists




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.