Graphene might be a promising material for spintronics
Spin transport, the magnetic property of electrons that, for instance, is being applied in readers of hard discs and magnetic RAM memories (RAM = Random Access Memory), passes in graphene at room temperature just as well as at very low temperatures. And also the fact that the spin is remaining its distance before changing direction, is relatively large. Moreover, the distance may be improved even of that order by using better fabrication techniques. All this is argued by researchers in the Zernike Institute for Advanced Materials at the University of Groningen and the FOM Foundation in The Netherlands, on basis of measurements they have been carrying out recently. So, graphene, a kind of layer of carbon only one atom thick and insulated from graphite for the first time three years ago, might be a promising material for spintronics. These findings will be published on-line in Nature on 15 July 2007.
Spintronics is based on the quantum mechanic property of electrons that is being called a 'spin'. A spin does not have a straight analogy in everyday life. However, in order to give you an idea, you may picture the electron as a spinning top that turns to the left or to the right. Due to this turning ('spin') the electron behaves like a tiny magnet, the magnetic field of which is able to point in two opposite directions ('spin-up' and 'spin-down'). Spintronics does not only use the transportation of electrons and thus, charge transport, but simultaneously it uses also the spin and the sensitivity of electrons to a magnetic field. This may lead to smaller, more solid and faster electronic circuits and media storage that has much larger data density than is usually feasible. Conditions are that the material being used, is magnetic or can be made magnetic and that the spin will be pointing in the desired direction long enough. The spins are being directed by using a magnetic field and they have to point in the same direction also after transport in order to be able to read out. Therefore, the fact that the spin remains its distance is of great importance.
The researchers at the University of Groningen have constructed a so-called spin valve by using graphene. Such a valve consists of non-magnetic material that is being inserted between two ferromagnets (materials that are magnetic by themselves). The researchers have been directing electrons that have one particular spin direction from one of the ferromagnets into the non-magnetic material. Then, the electrons are being detected again by the ferromagnet at the other side. The second ferromagnet only let the electrons pass that remained their original spin direction, also after moving through the non-magnetic material. In this state the electrical resistance of the spin valve decreases at large. If many spins are being swept down during transportation through the non-magnetic material, then the electrical resistance of the spin valve is increasing. The researchers measured this at three different temperatures (4.2 kelvin, 77 kelvin and 300 kelvin - i.e. room temperature). It appeared that the spin signal did not change signifiantly, which is a promising result in possible everyday use.
The research has also been made possible from a NWO-Pionier grant to Bart van Wees.
For more information, please contact Prof. B.J. van Wees, Rijksuniversiteit Groningen, phone (050) 363 48 26.
Reference:
Electronic spin transport and spin precession in single graphene layers at room temperature, Niko Trombos, Csaba Jozsa, Mihai Popinciuc*, Harry Jonkman and Bart van Wees, Nature, on-line on 15 July 2007.
* FOM PhD student