Topological Defects Induced High-Spin Quartet State in Truxene-Based Molecular Graphenoids

TL;DR

This study demonstrates that engineered topological defects in truxene-based molecular graphenoids can induce a collective high-spin state, advancing the design of molecular ferromagnetic materials with potential technological applications.

Contribution

It reveals how regular patterned topological defects can be used to engineer collective high-spin states in molecular graphenoids, a novel approach in molecular magnetism.

Findings

Unpaired electrons at pentagon defects are ferromagnetically coupled.

Formation of a collective high-spin S=3/2 state confirmed.

Engineered defects enable design of ferromagnetic spin networks.

Abstract

Topological defects in graphene materials introduce exotic properties which are absent in their defect-free counterparts with both fundamental importance and technological implications. Although individual topological defects have been widely studied, collective magnetic behaviors originating from well-organized multiple topological defects remain a great challenge. Here, we studied the collective magnetic properties originating from three pentagon topological defects in truxene-based molecular graphenoids by using scanning tunneling microscopy and non-contact atomic force microscopy. Unpaired $\pi$ electrons are introduced into the aromatic topology of truxene molecular graphenoids one by one by dissociating hydrogen atoms at the pentagon defects via atom manipulation. Scanning tunneling spectroscopy measurements together with density functional theory calculations suggest that the unpaired electrons are ferromagnetically coupled, forming a collective high-spin quartet state of S=3/2. Our work demonstrates that the collective spin ordering can be realized through engineering regular patterned topological defects in molecular graphenoids, providing a new platform for designer one-dimensional ferromagnetic spin chains and two-dimensional ferromagnetic networks.