Magnetic properties of graphene quantum dots

TL;DR

This study investigates the magnetic susceptibility of graphene quantum dots with various shapes and sizes, revealing how edge states influence their magnetic behavior, including diamagnetism and paramagnetism.

Contribution

It provides a detailed analysis of how different edge states in GQDs affect their magnetic properties, highlighting the role of geometry and size.

Findings

Hexagonal, circular, and random GQDs are mainly diamagnetic due to DES.

Triangular GQDs exhibit ZES and show a transition between paramagnetism and diamagnetism.

Edge states significantly influence the temperature-dependent magnetic response.

Abstract

Using the tight-binding approximation we calculated the magnetic susceptibility of graphene quantum dots (GQD) of different geometrical shapes and sizes, smaller than the magnetic length, when the magnetic properties are governed by the electron edge states. Two types of edge states can be discerned: the zero-energy states (ZES) located exactly at the zero-energy Dirac point, and the dispersed edge states (DES) with the energy close, but not exactly equal to zero. DES are responsible for the temperature independent diamagnetic response, while ZES provide the temperature dependent spin Curie paramagnetism. The hexagonal, circular and randomly shaped GQDs contain mainly DES and, as a result, they are diamagnetic. The edge states of the triangular GQDs are ZES and these dots reveal the interplay between the spin paramagnetism, dominating for small dots and at low temperatures, and bulk orbital diamagnetism, dominating for large dots and at high temperatures.