First-Principles Study of Substitutional Metal Impurities in Graphene: Structural, Electronic and Magnetic Properties

TL;DR

This study uses density functional theory to analyze how various metal atoms substitute into graphene vacancies, revealing their electronic, magnetic properties, and the regimes of hybridization that determine their behavior.

Contribution

It introduces a simple hybridization model to explain the electronic and magnetic properties of substitutional metal impurities in graphene.

Findings

Impurities like Sc and Ti are non-magnetic due to filled bonding states.

V, Cr, Mn exhibit large localized magnetic moments from partially filled d shells.

Zn impurity undergoes Jahn-Teller distortion with zero spin moment.

Abstract

We present a theoretical study using density functional calculations of the structural, electronic and magnetic properties of 3d transition metal, noble metal and Zn atoms interacting with carbon monovacancies in graphene. We pay special attention to the electronic and magnetic properties of these substitutional impurities and found that they can be fully understood using a simple model based on the hybridization between the states of the metal atom, particularly the d shell, and the defect levels associated with an unreconstructed D3h carbon vacancy. We identify three different regimes associated with the occupation of different carbon-metal hybridized electronic levels: (i) bonding states are completely filled for Sc and Ti, and these impurities are non-magnetic; (ii) the non-bonding d shell is partially occupied for V, Cr and Mn and, correspondingly, these impurties present large and localized spin moments; (iii) antibonding states with increasing carbon character are progressively filled for Co, Ni, the noble metals and Zn. The spin moments of these impurities oscillate between 0 and 1 Bohr magnetons and are increasingly delocalized. The substitutional Zn suffers a Jahn-Teller-like distortion from the C3v symmetry and, as a consequence, has a zero spin moment. Fe occupies a distinct position at the border between regimes (ii) and (iii) and shows a more complex behavior: while is non-magnetic at the level of GGA calculations, its spin moment can be switched on using GGA+U calculations with moderate values of the U parameter.