Magnetic and electronic phase crossovers in graphene nanoflakes

TL;DR

This study systematically explores how the magnetic and electronic phases of graphene nanoflakes can be manipulated through size, shape, and doping, revealing phase transitions and electronic property changes relevant for technological applications.

Contribution

It provides a detailed first-principles analysis of shape, size, and doping effects on magnetic and electronic phases in graphene nanoflakes, highlighting critical size and doping thresholds for phase transitions.

Findings

Magnetic phase transitions depend on flake size and shape.

Carrier doping induces magnetic and electronic phase changes.

Semiconductor to metal or half-metal transitions occur with doping.

Abstract

Manipulation of intrinsic magnetic and electronic structures of graphene nanoflakes is of technological importance. Here we carry out systematic study of the magnetic and electronic phases, and its manipulation in graphene nanoflakes employing first-principles calculation. We illustrate the intricate shape and size dependence on the magnetic and electronic properties, and further investigate the effects of carrier doping, which could be tuned by gate voltage. A transition from nonmagnetic to magnetic phase is observed at a critical flake size for the flakes without sublattice imbalance, which we identify to be originated from the armchair defect at the junctions of two sublattices on the edge. Electron, or hole doping simultaneously influences the magnetic and electronic structures, and triggers phase changes. Beyond a critical doping, crossover from antiferromagnetic to ferromagnetic phase is observed for the flakes without sublattice imbalance, while suppression of magnetism, and a possible crossover from magnetic to nonmagnetic phase is observed for flakes with sublattice imbalance. Simultaneous to magnetic phase changes, a semiconductor to (half) metal transition is observed, upon carrier doping.