Computer can use its own heat
Researchers from the University of Groningen and FOM have succeeded in transferring part of the magnetic moment from a magnet to another, non- magnetic metal using a heat flow. The transportation of a magnetic spin can be used to transfer information. This discovery could also lead to more efficient memory elements for modern solid-state computer hard disks, for example. The researchers published their results in the renowned journals Nature Physics (19 September) and Physical Review Letters (24 September).
The electrical writing of memory elements generates a considerable quantity of heat, an undesirable side effect. Researchers Abraham Slachter, Frank Bakker and Jean-Paul Adam from the FOM group of Bart van Wees have now demonstrated that this heat can also be put to good use. If this heat effect were to be cleverly put to work alongside the current technique for writing memory elements then the efficiency of this process could be significantly improved, say the researchers.
Spin
The magnetic moment of an electron, the 'spin', lays at the basis of magnetic data storage. In ferromagnets all of these spins point in the same direction, and together they form the magnetisation of the magnet. The data is recorded in magnetic domains, the 'bits'. Within such a domain, all spins are either pointing up (one) or down (zero). A relatively new and highly promising technique makes use of the exchange of spins between two magnetic layers for the writing and read-out of the memory elements. In the current technique, this is realised with the aid of an electric current. These completely electronic writable memory elements are better known as MRAM (Magnetic Random Access Memory) and are based on the spin-torque effect.
The research
Now the researchers have demonstrated that it is also possible to exchange spins using a heat flow and in so doing to write an MRAM cell. Their first experiment was set up to obtain more information about the heat released by memory elements. They demonstrated that heat flows exert a large effect on the electrical signals that are used to read out these memory elements. In addition to this they revealed that the heat profile can be 'read' with the help of thermo-electric measurements. In the second experiment they demonstrated that with the aid of a heated magnet, spins could be extracted and transported to a non-magnetic material. The heat effect was found to be large enough to be applied for writing memory elements in MRAM, and can therefore be used instead of or in addition to the electric current.
Spin-caloritronics
The results just published mark the birth 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 partly financed by the Foundation for Fundamental Research on Matter, the EU project DynaMax, NanoNed and the Zernike Institute for Advanced Materials.
Further information
For further information please visit the website www.nanodevices.nl or contact one of the researchers:
Bart van Wees, +31 (0)50 363 49 33,
Abraham Slachter, +31 (0)50 363 48 80,
Frank Bakker, +31 (0)50 363 89 73.
References
[1] 'Interplay of Peltier and Seebeck effects in nanoscale nonlocal spin valves', Physical Review Letters 2010
[2] 'Thermally driven spin injection from a ferromagnetic into a non-magnetic metal', Nature Physics 2010