Magnetic Properties of Graphene Functionalized with 2D Molecular Assemblies – MAGMA

Over the last decade, carbon nanotubes and graphene have been widely used to fabricate standard field-effect transistors (FET) and sensors. More recently, these materials have been considered for spintronic applications. Graphene, like carbon nanotubes, exhibits high electron mobility and weak spin-orbit coupling. This means that spin-polarized electrons can travel a long distance in graphene without losing their spin information. However, the weak Spin Orbit Interactions (SOI) precludes the electrically-driven reversal of spins that could lead to graphene or carbon nanotube-based spin-FETs. Recent theoretical studies have predicted that heavy element adatoms could increase the SOI in graphene while affecting the spin diffusion length only marginally. Beyond qualitative modifications of the transport, surface functionalization can radically change some of the electronic properties of graphene, by inducing both SOI and magnetism.
MAGMA is a fundamental collaborative research project which aims to create novel functionalities in graphene by controlled manipulation of the electron spins. To this end, we propose to functionalize graphene with arrays of organometallic complexes (metallated porphyrins and phthalocyanines) and to study how molecules deposited, either sparsely or in dense ordered networks, give rise to original versatile systems with tunable properties involving the spin degree of freedom of electrons. Depending on their nature/structure/property (defined by design) and their ability to exchange charges with graphene, the molecular complexes can either induce magnetism or Spin-Orbit Interactions in graphene.
Until recently, the influence of doping elements/molecules on graphene-based nanodevices and the supramolecular organization of metal complexes on graphene have been considered independently. The control over the formation of regular networks on graphene should lead to hybrid structures exhibiting perfectly adjustable properties. Our goal in the MAGMA project is to investigate the following fundamental questions:

- How do molecules self-organize on graphene? What is the influence of the type of graphene and of the underlying surface? How can one generate medium/long range ordered 2D networks?
- What are the possible charge exchange mechanisms between the molecules and graphene? How can the ionization state be tuned externally using the local electric field or the initial graphene doping?
- How does a network of molecules containing heavy elements induce SOI in graphene? What kind of SOI can one induce in graphene with these molecules and how can it be detected?

We will address these issues by combining chemistry, near-field characterization (Scanning Tunnelling Microscopy and Spectroscopy), theory, magnetism and device physics, including quantum electron transport at low temperature.
Preliminary results obtained on platinum porphyrins (PtP) deposited on graphene has not yet revealed SOI. However it was found, from magnetotransport measurements and by using the superconducting proximity effect that gate-controlled magnetism can be induced in graphene.