A Defective Graphene Phase Predicted to be a Room Temperature Ferromagnetic Semiconductor

TL;DR

This study predicts that defect-engineered graphene can be a room-temperature ferromagnetic semiconductor with tunable electronic and magnetic properties, promising for future spintronic applications.

Contribution

It introduces a new defect configuration in graphene that induces stable ferromagnetism at room temperature, with controllable electronic properties based on defect separation.

Findings

Defects induce long-range spin polarization in graphene.

The energy gap and magnetic coupling depend on defect separation.

Spin-dependent transport properties are predicted.

Abstract

Theoretical calculations, based on hybrid exchange density functional theory, are used to show that in graphene a periodic array of defects generates a ferromagnetic ground state at room temperature for unexpectedly large defect separations. This is demonstrated for defects that consist of a carbon vacancy in which two of the dangling bonds are saturated with H atoms. The magnetic coupling mechanism is analysed and found to be due to an instability in the $\pi$ electron system with respect to a long-range spin polarisation characterised by alternation in the spin direction between adjacent carbon atoms. The disruption of the $\pi$-bonding opens a semiconducting gap at the Fermi edge. The size of the energy gap and the magnetic coupling strength are strong functions of the defect separation and can thus be controlled by varying the defect concentration. The position of the semiconducting energy gap and the electron effective mass are strongly spin-dependent and this is expected to result in a spin asymmetry in the transport properties of the system. A defective graphene sheet is therefore a very promising material with an in-built mechanism for tailoring the properties of the spintronic devices of the future.