Interplay between opto-electronic response and edge magnetic coupling in graphene nanoflakes

The long spin-diffusion length, spin-lifetime and excellent optical absorption coefficient of graphene provide an attractive platform for building opto-electronic devices and spin-based logic in a nanometer regime. We analyze how the size and shape of graphene nanoflakes can be used to alter their magnetic structures and optical properties, using time-dependent density functional theory. As the edges of zigzag graphene nanoribbons are known to align anti-ferromagnetically and armchair ones are non-magnetic, a combination of both in a single nanoflake geometry can be used to optimize the ground-state magnetic structure to tailor the exchange coupling to ferro- or anti-ferromagnetic edge magnetism. This allows for optimizing the switching conditions between the two magnetic states, for example, tuning the energy-efficiency by countering the stability of the external field's magnitude. Additionally, we show that the magnetic ordering alters the optical response of the flake. Finally, we investigate how the high harmonic generation of a graphene nanoflake depends on its magnetic configuration and the polarization of the laser field.