Credit: © 2007 ACS

Graphene has a number of electronic properties that make it an ideal material for spintronics applications. The possibilities are all the more interesting for nanoscale graphene strips in which localized spins form along the edges owing to unpaired bonds.

A theoretical study from Efthimios Kaxiras and colleagues1 at Harvard University now explores the shape-dependent magnetic properties of graphene 'nanoflakes'. On the basis of a graphical analysis of the unpaired bonds of different graphene geometries — from triangles to complex looking snowflakes — the Harvard group predicts which shapes will have a finite spin. With the aid of first principle calculations, they determine how large this spin will be.

The spin on a triangular-shaped graphene flake scales linearly with the length of its side, or at least up to the point when the flake is a few nanometres in size. These flakes assume the properties of an infinite sheet of graphene. One other shape that is particularly interesting is a fractal 'star of David' in which it is shown that the spin state increases exponentially with the complexity — or fractal level — of the star edges.