Epitaxial graphene on metal for new magnetic nanometric systems

Orateur : Soutenance de thèse de Chi VO VAN (Institut Néel)

Graphene is a new candidate for spintronics due to its long spin diffusion length and high carrier mobility. In interaction with a ferromagnet or a hea vy element, it may reveal small magnetic moments, or a Rashba-split electronic band structure, respectively. These systems are playgrounds for exploring the manipulation of graphene properties by interaction with other species, and vice versa. Three hybrid systems were developed under ultra-clean conditions : cobalt ultra-thin films deposited on graphene, and intercalated between graphene and its substrate, and self-organized Co and Fe nanoclusters on the moiré pattern formed between graphene and Ir(111). Thin, high quality, Ir(111) films on sapphire were also developed, which advantageously can replace bulk single crystals that are usually employed for the growth of high quality graphene, in the prospect of multi-technique characterizations. Using in situ surface science techniques and ex situ probes, the structural, vibrational, electronic, and magnetic properties were characterized and confronted to first-principle calculations. The graphene/Co interface involves strong C -Co interactions which are responsible for a large interface magnetic anisotropy, driving out-of-plane magnetization in spite of the strong shape anisotropy in ultra-thin films. The effect is maximized in intercalated system, which comes naturally air-protected. Nanoclusters seem to weakly interact with graphene. Small ones of 30 atoms remain superparamagnetic at 10 K, have no magnetic anisotropy, and it is difficult to saturate their magnetization even with 5 T magnetic fields. Besides, the magnetic domains size seems to exceed the cluster size, possibly pointing to interactions between clusters.

Télécharger dans mon agenda