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Friday, 25 January 2013

Magnetically induced spin polarisation in graphene near EuO

Publishing in Physical Review Letters, a team including ICREA Professor and ICN Group Leader Dr Stephan Roche describes tuneable spin polarisation in graphene adjacent to europium oxide.

A team of researchers from France and Spain, led by Prof Mairbek Chshiev at SPINTEC, in Grenoble, and including ICREA Professor and ICN Group Leader Dr Stephan Roche, have just published in Physical Review Letters findings that evidence the possibility of induced spin polarisation in graphene by proximity effect of the magnetic insulator europium oxide (EuO). The paper, entitled "Proximity Effects Induced in Graphene by Magnetic Insulators: First-Principles Calculations on Spin Filtering and Exchange-Splitting Gaps", may have major implications for the development of spintronics devices such as memory chips.

Spintronics (from spin transport electronics) is a fledging field in which researchers are endeavouring to create devices that carry, store and process information encoded by electron spin, rather than by the traditional mode of electron charge. This requires the precise generation, maintenance and constant switching (up/down) of a spin-polarised (or pure spin) current. Although spintronics has already found practical applications in read-only devices (e.g. hard-drive heads), spintronics chips, in which spin currents must be continually generated and switched and must travel over relatively long distances, remain an elusive goal.

Among the challenges to creating spintronics chips is finding materials in which spin currents can be easily and selectively generated and controlled, and can travel, all at room temperature, which is required for real applications. The best candidates for this job include graphene, which is highly amenable to spin current transport and therefore, has garnered massive attention for its potential as a principal material for spintronics devices. However, additional materials would still be needed to selectively induce the shifts in electron spin inside of a graphene chip; basically, some type of magnetic "switch" would be needed to enable continuous selective control of the spin current. Magnetic insulators such as Europium oxide (EuO) are presently being explored as materials for this type of switch.

Prof Chshiev, Prof Roche and colleagues performed ab initio calculations of a system comprising a thin film of EuO covering a graphene monolayer, in which they computed the structure and spin-dependent properties of the EuO-graphene junctions (the bridging areas where the electrons of the two materials interact). They observed magnetic interaction between the two materials and found that the EuO caused heterogeneous spin polarisation (i.e. different levels of net spin in different areas) in the graphene at impressive values (average: 24%; local maximum: 30%). Furthermore, thismagnetic proximity effect was tuneable, meaning that they were able to control the level of spin polarisation by adjusting the position of the Fermi level.

Lastly, the researchers found that the system was quite robust: when incorporated environmental effects such as pressure and strain into their calculations, they found that the consequences on spin polarisation were minimal.

The team concluded the article by affirming the need for experimental investigation of their simulation results and highlighting a recent report of fabrication of EuO on graphene.

To access the article, “Proximity Effects Induced in Graphene by Magnetic Insulators: First-Principles Calculations on Spin Filtering and Exchange-Splitting Gaps”, click here.