Physics Colloquium: On the Road to the Defect-induced FerroGraphene

Graphene, a one-atom-thick sheet of carbon atoms arranged in a honeycomb lattice, is the first and the most well studied two-dimensional material. Despite its superlative electronic and mechanical properties, it is only diamagnetic with negligible response to a magnetic field. Since its isolation in 2004 from graphite, a relentless quest has been started to magnetize graphene in order to give birth to the first, metal-free, lightweight, and biocompatible magnet, whose magnetism could be switched on and off by applying a tiny electric field. Such a magnet can have promising applications in biomedicine and potentially lead to miniaturization of future magnetic sensors and data storage devices to an unprecedented level.

There is by now significant theoretical and experimental evidence that the defects such as vacancies (missing carbon atoms) or adsorbates such as hydrogen can induce localized or itinerant (delocalized) magnetic moments in this otherwise nonmagnetic material. Nevertheless, the realization of the defect-induced ferromagnetic graphene at room temperature remains elusive and highly contentious experimentally while the key theoretical issues have yet to be addressed. One of the main theoretical challenges is the inadequate treatment of the interaction between the induced magnetic moment and graphene electrons, hence the possibility of the Kondo effect leading to the quenching of the magnetic moment. Moreover, a complete understanding of the magnetic ordering requires an effective simulation of the collective interactions between random distributions of such defects mediated by interacting graphene electrons. This demonstrates the paramount need for a theoretical method that offers not only an explicit treatment of electron correlations, but also a controlled simulation of realistically large systems.

In this talk I will present the current status of the defect-induced magnetism in carbon-based materials and, in particular, discuss the origins of the controversies in the Kondo problem and magnetic ordering in graphene. Then, I will present my contributions to our understanding of the nature of the defect-induced magnetic moments in disordered graphene, and the magnetic interactions between the localized moments in the material, namely the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction. I will then briefly introduce a robust, nonperturbative correlation-calculation method known as the Gutzwiller variational method and argue how it meets both the above-mentioned requirements. Finally, I outline my proposal for a comprehensive addressing of the defect-induced ferromagnetic graphene based on using the Gutzwiller method, which may open a promising chapter in our quest for the sought after FerroGraphene.