# Engineering Correlation-Driven Magnetism by Atomic Substitution in Metal-Free Phenalenyl-Based Two-Dimensional Polymers

## TL;DR

This paper explores how atomic substitution in metal-free 2D polymers can control magnetic properties through electronic correlations and sublattice symmetry.

## Contribution

The study introduces a framework for tuning magnetism in metal-free 2D polymers via atomic substitution, linking electronic correlation and sublattice symmetry.

## Key findings

- Sublattice-asymmetric substitution with boron or nitrogen induces spin-polarized semiconducting phases.
- Uniform substitution preserves symmetry and results in nonmagnetic metallic states.
- Electronic correlations and sublattice symmetry are shown to be independently tunable parameters.

## Abstract

Metal-free two-dimensional (2D) polymers built from open-shell π-conjugated units offer a promising platform for realizing correlation-driven magnetism without transition metal elements. Here, we present a systematic first-principles study of phenalenyl-based 2D polymers that elucidates how atomic-level chemical substitution controls magnetic order through the interplay of electronic correlation and sublattice symmetry. Combining density functional theory with an effective tight-binding and Hubbard model analysis, we show that atomic substitution with boron or nitrogen on phenalenyl building blocks acts as a sublattice-resolved tuning knob for both the ratio of on-site Coulomb interaction to inter-site hopping (U/t) and the relative on-site energies of the two sublattices. Sublattice-asymmetric substitution with boron or nitrogen breaks sublattice equivalence and drives the system from an antiferromagnetic Mott-insulating state into spin-polarized semiconducting phases with pronounced spin-dependent gaps. In contrast, uniform substitution on both sublattices preserves symmetry and yields nonmagnetic metallic states characterized by rigid band shifts rather than correlation-driven spin polarization. These results establish a unified microscopic framework in which electronic correlations and sublattice symmetry emerge as cooperative yet independently tunable parameters, providing general design principles for metal-free 2D π-conjugated materials with tailored magnetic and spintronic functionalities.