Magnetism in strained graphene dots

TL;DR

This study investigates how strain and edge structure influence magnetization in graphene dots, revealing phase transitions, edge state behaviors, and significant magnetization enhancement under strain, with potential implications for nano-magnetic devices.

Contribution

It demonstrates the effects of uniaxial strain and edge configurations on magnetization and phase transitions in graphene dots, including the absence of zero energy edge states in certain hexagonal dots.

Findings

Hexagonal dots exhibit a second order phase transition at a critical Hubbard energy.

Uniaxial strain can enhance magnetization by up to 100%.

Stress shifts magnetization from zig-zag to armchair edges.

Abstract

We study the magnetization of square and hexagonal graphene dots. It is shown that two classes of hexagonal dots have a second order phase transition at a critical Hubbard energy $U$, whoose value is similar to the one in bulk graphene, albeit the dots do not have a density of states proportional to the absolute value of the energy, relatively to the Dirac point. Furthermore, we show that a particular class of hexagonal dots having zig-zag edges, does not exhibit zero energy edge states. We also study the effect of uniaxial strain on the evolution of the magnetization of square dots, and find that the overall effect is an enhancement of magnetization with strain. The enhancement can be as large as 100% for strain of the order of 20%. Additionaly, stress induces a spatial displacement of the magnetization over the dot, moving it from the zig-zag to the armchair edges.