May 10, 2013

New magnetic graphene may revolutionise electronics with graphene spintronics

Researchers from IMDEA-Nanociencia Institute and from Autonoma and Complutense Universities of Madrid (Spain) have managed to give graphene magnetic properties. The breakthrough opens the door to the development of graphene-based spintronic devices, that is, devices based on the spin or rotation of the electron, and could transform the electronics industry.

Computerised simulation of TCNQ molecules on graphene layer, where they acquire a magnetic order. / IMDEA-Nanoscience

Nature Physics - Long-range magnetic order in a purely organic 2D layer adsorbed on epitaxial graphene

The technique involves growing an ultra perfect graphene film over a ruthenium single crystal inside an ultra high vacuum chamber where organic molecules of tetracyano-p-quinodimethane (TCNQ) are evaporated on the graphene surface. TCNQ is a molecule that acts as a semiconductor at very low temperatures in certain compounds.

On observing results through an scanning tunnelling microscope (STM), scientists were surprised: organic molecules had organised themselves and were regularly distributed all over the surface, interacting electronically with the graphene-ruthenium substrate.

"We have proved in experiments how the structure of the TCNQ molecules over graphene acquires long-range magnetic order, with electrons positioned in different bands according to their spin," clarifies Prof. Amadeo L. Vázquez de Parga.

Meanwhile, his colleague Prof. Fernando Martin has conducted modelling studies that have shown that, although graphene does not interact directly with the TCNQ, it does permit a highly efficient charge transfer between the substrate and the TCNQ molecules and allows the molecules to develop long range magnetic order.

The result is a new graphene-based magnetised layer, which paves the way towards the creation of devices based on what was already considered as the material of the future, but which now may also have magnetic properties.

ABSTRACT - Collective magnetic properties are usually associated with the d or f electrons that carry the individual magnetic moments. A fully spin-polarized ground state based on π electrons has been predicted in half-filled flat-band organic materials, but has remained experimentally challenging to realize. Here we show that isolated tetracyano- p-quinodimethane molecules deposited on graphene epitaxially grown on Ru(0001) acquire charge from the substrate and develop a magnetic moment of 0.4 μB per molecule. The magnetic moment survives even when the molecules form into a dimer or a monolayer, with a value of 0.18 μB per molecule for the monolayer. The self-assembled molecular monolayer develops spatially extended spin-split electronic bands, and we visualized the ground-state spin alignment using spin-polarized scanning tunnelling microscopy. The observation of long-range magnetic order in an organic layer adsorbed on graphene paves the way for incorporating magnetic functionalities into graphene.

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