Researchers from the University of Groningen and the Foundation for Fundamental Research on Matter (FOM) have developed a technique to simply measure the magnetic moment of electrons (the spin) using non-magnetic contacts. They demonstrated the technique in graphene, a layer of carbon one atom thick. The use of non-magnetic contacts could yield simpler designs for nano-devices that use spin current. Such equipment is currently used in hard discs to make these faster and more efficient. The researchers published their results on 12 February 2012 online in the renowned journal Nature Physics.
Graphene is a two-dimensional material with superb characteristics for the transport of charge and spin, the two fundamental properties of an electron. Graphene is not magnetic and therefore magnetic information must first of all be 'added' before spin transport can be studied in it. The researchers did this by transmitting electric current through magnetic contacts, which set the spin of all the electrons in the graphene in the same direction. As the electrons move, this results in a spin current, which can only be used in devices if it is detected. Previously this could only be done using other magnetic contacts further up in the circuit. Now simpler non-magnetic contacts can also be used for this.
The detection technology is based on a new physical mechanism that converts spin current back into voltage again in the graphene, which can be measured directly using non-magnetic contacts. This translation step is similar to the conversion of heat into an electric current, as happens in thermoelectric generators that use waste heat to drive electronic circuits. Both processes make use of the energy-dependent conduction of electrons. This means that the energy of the electrons determines how easily these move, and so how well the material (in this case graphene) conducts. The energy of the electrons is in turn dependent on their magnetic properties or – in the case of thermoelectric generators – the heat of the material.
The results are important for the development of spintronics (spin electronics) a new research area that studies the role of the magnetic moment of electrons in electronic equipment. Equipment based on these magnetic characteristics is potentially faster and more efficient.
For further information you can visit www.nanodevices.nl or contact one of the researchers:
Bart van Wees
Ivan Vera Marun
Reference 'Nonlinear detection of spin currents in graphene with non-magnetic electrodes', I. J. Vera-Marun, V. Ranjan and B. J. van Wees, Nature Physics (2012) DOI: 10.1038/NPHYS2219
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