A 50-year quest to isolate the thermoelectric effect is now over: Magnon drag unveiled

Dec 18, 2011

In a paper published in Nature Materials, a group of researchers at the Catalan Institute of Nanotechnology (ICN, Spain) led by Prof. Sergio O. Valenzuela reports the observation of the magnon drag. This work ends a 50-year long effort to isolate this elusive thermoelectric effect.

As move past atoms in a solid, their charge distorts the nearby lattice and can create a wave. Reciprocally, a wave in the lattice affects the electrons motion, in analogy to a wave in the sea that pushes a surfer riding it. This interaction results in a thermoelectric effect that was first observed during the 1950's and has come to be known as phonon-drag, because it can be quantified from the flow of lattice-wave quanta () that occurs over the .

Soon after the discovery of the phonon drag, an analogous phenomenon was predicted to appear in : the so called magnon drag. In a magnetic material the intrinsic or spin of the electrons arrange in an organized fashion. In ferromagnets, the spins maintain a parallel orientation. If a distortion in the preferred spin orientation occurs, a spin wave is created that could affect . It is therefore reasonable to expect that the flow of magnons ( quanta) could also drag the electrons.

Despite the similarities with phonon drag, the observation of the magnon drag has been elusive, and only a few indirect indications of its existence have been reported over the years. The main reason being the presence of other thermoelectric effects, most notably the phonon drag, that make it difficult to discriminate its contribution to the thermopower.

Researchers of ICN's Physics and Engineering of Nanodevices Group, Marius V. Costache, Germán Bridoux, Ingmar Neumann and group leader ICREA Prof. Sergio O. Valenzuela used a unique device geometry to discriminate the magnon drag from other thermoelectric effects. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon drag thermoelectric effects.

The work is very timely as thermoelectric effects in spin-electronics (spintronics) are gathering increasing attention as a means of managing heat in nanoscale structures and of controlling spin information by using heat flow. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. This information is crucial to understand the physics of thermal spin transport. It both provides invaluable opportunities to gather knowledge about electron-magnon interactions and may be beneficial for energy conversion applications and for the search of novel pathways towards transporting spin information.

Explore further: Breakthrough in OLED technology

More information: “Magnondrag thermopile” Nature Materials (2011) dx.doi.org/10.1038/NMAT3201

Related Stories

Research reveals vital insight into spintronics

Jul 03, 2011

(PhysOrg.com) -- Progress in electronics has relied heavily on reducing the size of the transistor to create small, powerful computers. Now spintronics, hailed as the successor to the transistor, looks set ...

Generation of spin current by acoustic wave spin pumping

Sep 26, 2011

Tohoku University, Japan Science and Technology Agency (JST) and Japan Atomic Energy Agency (JAEA) announced on August 22, 2011 that Kenichi Uchida, a PhD student, and Professor Eiji Saitoh of Tohoku University and their ...

Recommended for you

Breakthrough in OLED technology

12 hours ago

Organic light emitting diodes (OLEDs), which are made from carbon-containing materials, have the potential to revolutionize future display technologies, making low-power displays so thin they'll wrap or fold ...

Throwing light on a mysterious human 'superpower'

15 hours ago

Most people, at some point in their lives, have dreamt of being able to fly like Superman or develop superhuman strength like the Hulk. But very few know that we human beings have a "superpower" of our own, ...

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

knowledge_treehouse
not rated yet Dec 19, 2011
Electron shell parity is required for magnetic domains

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.