Ground-state magnetic phase diagram of bow-tie graphene nanoflakes in external magnetic field

Abstract

The magnetic phase diagram of a ground state is studied theoretically for graphene nanoflakes of bow-tie shape and various size in external in-plane magnetic field. The tight-binding Hamiltonian supplemented with Hubbard term is used to model the electronic structure of the systems in question. The existence of the antiferromagnetic phase with magnetic moments localized at the sides of the bow-tie is found for low field and a field-induced spin-flip transition to ferromagnetic state is predicted to occur in charge-undoped structures. For small nanoflake doped with a single charge carrier the low-field phase is ferrimagnetic and a metamagnetic transition to ferromagnetic ordering can be forced by the field. The critical field is found to decrease with increasing size of the nanoflake. The influence of diagonal and off-diagonal disorder on the mentioned magnetic properties is studied. The effect of off-diagonal disorder is found to be more important than this of diagonal disorder, leading to significantly widened distribution of critical fields for disordered population of nanoflakes.

Improved All-Carbon Spintronic Device Design

“…Bow-tie graphene nanoflakes, also known as Clar's goblet (Figure 1 (b)), constitute another class of popular structures17. Bow-ties have been predicted to show potential application as spin filters or as switches3637.…”

“…While each of these individual structures have interesting properties, spin alignment between graphene layers can become coupled, allowing for more complicated device designs16. Simulations have demonstrated that external magnetic fields can change the spin ordering on zigzag edges17, and even static electric fields might have the potential to influence the spin properties of nanostructured carbon1819. Carbon chain links have been proposed as another method of transferring spin information between flakes20, and theoretical studies using metal contacts and side groups have been published2122.…”

Graphene nanoflakes in external electric and magnetic in-plane fields

“…These electrons contribute the energy states close to the Fermi level for charge-neutral nanoflakes. In the present work we describe the behaviour of the mentioned charge carriers by means of the following tight-binding based Hamiltonian in real space: [63,81]…”

“…1) can be decomposed into the form of H = H ↑ + H ↓ − U i n i,↑ n i,↓ . Then the pair of Hamiltonians H ↑ , H ↓ can be subject to simultaneous, self-consistent numerical diagonalization starting from random initial conditions for n i,σ until the convergence of eigenvalues ǫ σ i as well as convergence of charge densities n i,σ is reached [63,81,102]. In the present work we used LAPACK [106] package for this purpose.…”

“…Within this scope of studies, the electric field focuses dominant attention, both in the context of graphene itself [44][45][46][47][48][49][50][51], its cousin systems [52][53][54][55] as well as for derivative nanostructures, like monolayer and bilayer graphene nanoflakes (quantum dots) [21,[56][57][58][59][60][61][62][63][64][65][66][67], nanoribbons [35,[68][69][70][71][72][73][74][75][76] or nanotubes [77]. The effect of magnetic field on magnetism in graphene-based structures has been also investigated [24,[78][79][80][81][82]. However, it is rather rare to study the common influence of both fields on the properties of graphene [83,84].…”