Universal Magnetic Properties of sp$^3$-type Defects in Covalently Functionalized Graphene

TL;DR

This study demonstrates that covalent functionalization of graphene with sp$^3$ defects induces universal magnetic properties, largely independent of the specific adsorbates, with potential applications in chemical engineering of magnetic graphene derivatives.

Contribution

It reveals that sp$^3$-type defects create universal magnetic moments in graphene regardless of the adsorbates, and details the sublattice-dependent magnetic coupling mechanisms.

Findings

A local spin-moment of 1.0 μB appears with covalent bonds.

Ferromagnetic coupling occurs between adsorbates on the same sublattice.

Magnetic properties are similar even with multiple saturated p_z orbitals.

Abstract

Using density-functional calculations, we study the effect of sp$^3$-type defects created by different covalent functionalizations on the electronic and magnetic properties of graphene. We find that the induced magnetic properties are {\it universal}, in the sense that they are largely independent on the particular adsorbates considered. When a weakly-polar single covalent bond is established with the layer, a local spin-moment of 1.0 $\mu_B$ always appears in graphene. This effect is similar to that of H adsorption, which saturates one $p_z$ orbital in the carbon layer. The magnetic couplings between the adsorbates show a strong dependence on the graphene sublattice of chemisorption. Molecules adsorbed at the same sublattice couple ferromagnetically, with an exchange interaction that decays very slowly with distance, while no magnetism is found for adsorbates at opposite sublattices. Similar magnetic properties are obtained if several $p_z$ orbitals are saturated simultaneously by the adsorption of a large molecule. These results might open new routes to engineer the magnetic properties of graphene derivatives by chemical means.