New nanoscale cooling element works in electrical insulators as well

July 8, 2014 by Ans Hekkenberg, Fundamental Research on Matter (FOM)

The sample used for the measurement. In the middle, from top to bottom, is the platinum strip. Electrons move through this strip and produce a spin current in the direction of the underlying insulator. The spins of the electrons that reach the boundary ensure that the spins in the insulator become excited. Two zigzag shaped thermometers made from platinum and constantan measure the temperature difference close to the boundary. Credit: Fundamental Research on Matter (FOM)
( —Researchers from the FOM Foundation, the University of Groningen, Delft University of Technology and Tohoku University in Japan have designed a miniscule cooling element that uses spin waves to transport heat in electrical insulators. The cooling element could be used to dissipate heat in the increasingly smaller electrical components of computer chips. The researchers published their design online on 7 July 2014 in Physical Review Letters.

The functioning of the cooling element is based on the spin of the . Spin is a fundamental property of an electron that corresponds with its (the strength and direction of its ). Although physicists have used spin for cooling purposes before, this is the first time that they have successfully done this in insulating materials.

Heat transport through a nanopillar

In previous research, the scientists let a current of electrons flow through magnetic metals. In a magnetic field, the spins of these electrons will align in the same direction, namely parallel to the magnetisation. The researchers sent the electrons through a pillar that consisted of two magnetic layers (with a non-magnetic layer in between). The pillar used was miniscule – about a thousand times smaller than the thickness of a human hair.

An electron that starts in the bottom layer aligns its spin to the direction of magnetisation in that layer. Subsequently the electron flows to the top layer. If the direction of magnetisation there is the same as in the bottom layer then the spin is still oriented parallel to the magnetisation. Electrons with a parallel spin direction transport more heat than electrons with an opposite spin direction. So in this case, the electrons ensure that a lot of heat is transported through the entire pillar. If the electrons, however, encounter a magnetisation in the opposite direction in the top layer, the is suppressed. Using this knowledge the researchers successfully caused a measurable temperature difference between the two sides of the pillar.

Spin waves

This method does not work in an electrical insulator – a material that does not easily conduct electrons. Nevertheless, the researchers have now found a cooling method that also works in insulating materials. In the new research they demonstrated that the spins on the boundary between a non-magnetic metal and a magnetic insulator cause so-called that transport heat to or from the material.

The researchers used a 200-nanometre thick insulator of yttrium-iron garnet (a mineral) with a 20 by 200 micrometre layer of platinum on top. Electrons can easily flow through the conducting platinum but when they reach the insulating garnet they cannot go any further. Nevertheless, the spin of the electrons is transferred: the magnetic moment of the electron influences the magnetic moment (and therefore the spin) of the electrons in the insulator that are at the boundary between the two materials. Through magnetic coupling this spin change is subsequently transferred to electrons that are situated further away from the boundary. In this manner a wave of spin changes appears to proceed through the material. The spin wave also transfers heat to or from the boundary. Dependent on the of both the and the magnetisation in the mineral, the boundary will therefore cool down or up.


The researchers placed small, highly sensitive thermometers just a few micrometres away from the boundary and used these to detect the temperature differences while electrons flowed through the platinum strip. The physicists subsequently compared their measurements with the above-mentioned theory. The temperature differences, just 0.25 millicelsius in size, appear to confirm the theory.

This research was jointly funded by the FOM Foundation, NanoLab NL, JSPS, the Deutsche Forschungsgemeinschaft, EU-FET Grant InSpin 612759 and the Zernike Institute for Advanced Materials.

Explore further: Theoretical device could bring practical spintronics closer to reality

More information: Observation of the Spin Peltier Effect for Magnetic Insulators, Phys. Rev. Lett. 113, 027601. … ysRevLett.113.027601

The American Physical Society published a viewpoint on this study:

Related Stories

Ti-V alloys' superconductivity: Inherent, not accidental

June 23, 2014

Physicists from India have shed new light on a long-unanswered question related to superconductivity in so-called transition metal binary alloys. The team revealed that the local magnetic fluctuations, or spin fluctuations, ...

Exploring the magnetism of a single atom

May 8, 2014

Magnetic devices like hard drives, magnetic random access memories (MRAMs), molecular magnets, and quantum computers depend on the manipulation of magnetic properties. In an atom, magnetism arises from the spin and orbital ...

Using heat to make magnets

October 17, 2013

EPFL scientists have provided the first evidence ever that it is possible to generate a magnetic field by using heat instead of electricity. The phenomenon is referred to as the Magnetic Seebeck effect or 'thermomagnetism'.

Magnetism in thin insulating films at room temperature

October 18, 2012

(—Researchers at the University of Twente's MESA+ Institute for Nanotechnology have succeeded in producing ultrathin films with an unusual combination of properties. At room temperature they do not conduct electricity, ...

Spintronics: Deciphering a material for future electronics

February 3, 2014

Topological insulators are the key to future spintronics technologies. EPFL scientists have unraveled how these strange materials work, overcoming one of the biggest obstacles on the way to next-generation applications.

Recommended for you

Researchers make coldest quantum gas of molecules

February 21, 2019

JILA researchers have made a long-lived, record-cold gas of molecules that follow the wave patterns of quantum mechanics instead of the strictly particle nature of ordinary classical physics. The creation of this gas boosts ...

Sculpting stable structures in pure liquids

February 21, 2019

Oscillating flow and light pulses can be used to create reconfigurable architecture in liquid crystals. Materials scientists can carefully engineer concerted microfluidic flows and localized optothermal fields to achieve ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

3.5 / 5 (4) Jul 08, 2014
Yttrium-iron garnet (YIG) is not a typical insulator, and the article should not imply that this technique will work for other insulators. YIG is ferrimagnetic, has a very strong Faraday effect, (rotating light polarization proportionally to applied magnetic field), tiny electron-spin resonance linewidth, a super -narrow bandwidth (high Q) when used for microwave resonators (as in high-end spectrum analyzers) and also low red / infrared absorption. YIG is as close to a magic crystal as you'll find in the real world.

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.