Nanoscale cooling element can be controlled magnetically

Researchers from the University of Groningen have developed a nanoscale cooling element that can be switched on and off magnetically. The functioning of the elements is based on the magnetic moment of the electrons (the spin). These easily controllable nanoscale cooling elements could provide a solution for the growing problem of heat production in increasingly smaller electronic components.

The researchers published their results 5 February online in the renowned journal Nature Nanotechnology. The research was financed by the FOM Foundation.

Each electron has a magnetic moment or 'spin'. When an electric current is sent through a magnetic layer the spins of the electrons in the current all point the same way (parallel to the magnetisation). Therefore in addition to the flow of charge a flow of spin arises. The researchers have demonstrated that such a spin current can be used to influence the temperature on a surface boundary between a non-magnetic metal and a magnetic metal. By reversing the magnetisation (spin direction) in one of the magnetic layers the cooling of the surface boundary can be switched on and off. The effect is therefore programmable.

Nanothermometer

In the experiment, the researchers used a nanopillar consisting of two magnetic layers with a non-magnetic layer in between. When they sent a current through this pillar, spin currents developed that flowed from one magnetic layer through the non-magnetic layer to the other magnetic layer. In the magnetic layers, electrons with the one spin direction transported more heat than electrons with the other spin direction giving rise to a temperature difference. The researchers measured this difference using a specially designed nano-sized thermometer that they positioned close to the pillar.

Spin caloritronics

The results just published mark the dawn of 'spin-caloritronics', a new research area within spin electronics that studies the role of the magnetic moment of electrons in heat transport.

This research was jointly funded by the Foundation for Fundamental Research on Matter (FOM), EU FP7 ICT Grant No. 251759 MACALO, NanoLabs and the Zernike Institute for Advanced Materials.

Reference
'Direct observation of the spin-dependent Peltier effect', J. Flipse, F.L. Bakker, A. Slachter, F. K. Dejene and B.J. van Wees, Nature Nanotechnology (2012) DOI: 10.1038/NNANO.2012.2