Origin of $sp$-electron magnetism in Graphitic Carbon Nitride

TL;DR

This paper explains how $sp$-electron magnetism can arise in non-magnetic materials through partial occupation of antibonding states, demonstrated in graphitic carbon nitride with a vacancy, revealing a new magnetic mechanism.

Contribution

It uncovers a novel mechanism for $sp$-electron magnetism based on first principles calculations in a specific carbon nitride structure.

Findings

Magnetism originates from partial occupation of antibonding states.

Antibonding wavefunctions are spatially antisymmetric, leading to spin symmetry.

$g$-C$_4$N$_3$$ exhibits a 1 μB magnetic moment due to antibonding state occupation.

Abstract

Based on first principles calculations, this study reveals that magnetism in otherwise non-magnetic materials can originate from the partial occupation of antibonding states. Since the antibonding wavefunctions are spatially antisymmetric, the spin wavefunctions should be symmteric according to the exchange antisymmetric principle of quantum mechanics. We demonstrate that this phenomenon can be observed in a graphitic carbon nitride material, $g$-C$_4$N$_3$, which can be experimentally synthesized and seen as a honeycomb structure with a vacancy. Three dangling bonds of N atoms pointing to the vacancy site interact with each other to form one bonding and two antibonding states. As the two antibonding states are near the Fermi level, and electrons should partially occupy the antibonding states in spin polarization, this leads to 1~$\mu_B$ magnetic moment.