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11-10 :: October 2011
nanotimes News in Brief
Today, magnetic tunnel structures already occur in various areas of information technology. They are used, for example, as magnetic storage cells in non-volatile magnetic memory chips (the so-called MRAMs – Magnetic Random Access Memories) or as highly sensitive magnetic sensors to read out the data stored on hard disks. The new effect discove- red at German PTB (national metrology institute) within the scope of a research collaboration with Bielefeld University and the Singulus company could, in the future, add a new application to the existing ones: monitoring and controlling thermo- electric voltages and currents in highly integrated electronic circuits.
Magnetic tunnel structures consist of two magnetic layers separated only by a thin insulation layer of approx. 1nm - the so-called “tunnel barrier”. The magnetic orientation of the two layers inside the tunnel structure has a great influence on its electri- cal properties: if the magnetic moments of the two layers are parallel to each other, the resistance is low; if, on the contrary, they are opposed to each other, the resistance is high. The change in the resistance when switching the magnetisation can amount to more than 100%. It is therefore possible to control the electric current flowing through the magnetic tunnel structure efficiently by simply swit- ching the magnetisation.
The work carried out by the PTB researchers now shows that, besides the electric current, also the thermal current flowing through the tunnel struc- ture can be influenced by switching the magne- tisation. In their experiments, the scientists gene- rated a temperature difference between the two magnetic layers and investigated the electric voltage
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(the so-called “thermoelectric voltage”) generated hereby. It turned out that the thermoelectric voltage depends on the magnetic orientation of the two layers nearly as strongly as the electric resistance. By switching the magnetisation, it is therefore possible to control the thermoelectric voltage and, ultima- tely, also the thermal current flowing through the specimen.
N. Liebing, S. Serrano-Guisan, K. Rott, G. Reiss, J. Langer, B. Ocker, and H.W.Schumacher: Tunneling magneto po- wer in magnetic tunnel junction nanopillars, In: Physical Review Letters, Vol. 107(2011), Issue 17, October 21, 2011, Article 177201 [4 pages], DOI:10.1103/PhysRev- Lett.107.177201:
http://prl.aps.org/abstract/PRL/v107/i17/e177201
A team from Cambridge‘s Department of Enginee- ring added a tiny amount of gold to the surface of a nickel film, on which graphene was then grown. The resulting allow enabled graphene to be grown at 450° C (842° F), as opposed to the 1,000° C (1,832° F) that is normally required.
A team of electrical engineers at Vanderbilt Univer- sity has developed all the basic components nee- ded to create microelectronic devices out of thin