Understanding the $sp$ magnetism in substitutional doped graphene

TL;DR

This study investigates the origin of $sp$ magnetism in substitutionally doped graphene, revealing that charge doping and hybridization are key factors in the emergence of magnetic behavior.

Contribution

It provides a detailed theoretical analysis of how specific impurities induce magnetism in graphene, highlighting the roles of charge transfer and hybridization.

Findings

Magnetism arises from an electronic instability due to a narrow impurity band at the Fermi level.

Spin polarization requires the impurity to add an extra electron to the graphene lattice.

Impurity-carbon hybridization close to $sp^3$ geometry is essential for $sp$ magnetism.

Abstract

Defect-induced magnetism in graphene has been predicted theoretically and observed experimentally. However, there are open questions about the origin of the magnetic behavior when substitutional impurities with $sp$ electrons are considered. The aim of this work is to contribute to the understanding of impurity-induced spin magnetism in doped graphene systems. Thus, the electronic structure and spin magnetic moments for substitutional doped graphene with impurities from groups IIIA (B, Al, and Ga) and VA (N, P, As, Sb, and Bi) of the periodic table were obtained within the framework of density functional theory. The nature of the magnetic ground state was determined from calculations of the total energy as a function of the spin magnetic moment using the fixed spin moment method. We show that the spontaneous magnetization in the studied systems arises from an electronic instability by the presence of a narrow impurity band at the Fermi level. Furthermore, we found that the emergence of spin polarization requires the impurity to introduce an extra electron to the graphene lattice and that the impurity-carbon hybridization is close to the $sp^3$ geometry. These features reveal that the charge doping sign and the hybridization degree play a fundamental role in the origin of $sp$ magnetism in substitutional doped graphene.