Theoretical Study Of Magnetism Of Graphene Nanoribbons

Graphene is two-dimensional honeycomb crystals of carbon, attracting the attention of entire scientific community for its fascinating properties. These excellent properties make graphene a potential substitute of silicon in electronics, therefore revolution may happen. It is key to realize the magnetism of graphene nanoribbons and how to control that. In this paper, we study the magnetism of graphene nanoribbons and zigzag square lattice by the mean-field approximation and self-consistent calculation.The paper is divided into four chapters. The first chapter is the introduction. We briefly introduce the unique physical properties, synthesis and applications of graphene, and mainly introduce the methods to make graphene, graphene nanoribbons and graphene nanoclusters magnetic; The second chapter is the preparatory work for exploring the magnetism of graphene, we learned and understood the band structure of zigzag graphene nanoribbons and armchair graphene nanoribbons.The third chapter is the main content in this paper, we explored the magnetism of zigzag graphene nanoribbons. Theoretical calculations reveal that ferromagnetic coupling and anferromagnetic couping occur randomly on the two edges of the same zigzag graphene nanoribbon,but the probability of antiferromagnetic coupling is greater than that of ferromagnetic coupling with width less than 8 nanometers. The ribbons are semiconductor with the anferromagnetic coupling and display quantum confinement gaps; The ribbons are conductor with the ferromagnetic coupling. In either case, the magnetism of atom on the ribbons edges is a constant value, and does not change according to the width of graphene. We also explored the magnetism of the zigzag square lattice. We found that the system also appears ferromagnetic coupling and antiferromagnetic coupling on either side, and the free energy of antiferromagnetic coupling is always less than the free energy of ferromagnetic coupling. When combined with zeeman field, the system appears antiferromagnetic-ferromagnetic phase transition, eventually leaving ferromagnetic coupling. The fourth chapter are the conclusions and outlook.