Building spin-1/2 antiferromagnetic Heisenberg chains with diaza-nanographenes

TL;DR

This paper reports the synthesis and characterization of spin-1/2 antiferromagnetic Heisenberg chains using diaza-nanographenes, demonstrating controlled odd-even magnetic effects with potential applications in nanoscale spintronics.

Contribution

It introduces a novel on-surface synthesis method for nanographene spin chains with parity-dependent magnetization, advancing quantum magnetic material design.

Findings

Successful synthesis of diaza-HBC spin chains with odd-even effects

Observation of gapped excitations in even chains

Enhanced Kondo resonance in odd chains

Abstract

Understanding and engineering the coupling of spins in nanomaterials is of central importance for designing novel devices. Graphene nanostructures with {\pi}-magnetism offer a chemically tunable platform to explore quantum magnetic interactions. However, realizing spin chains bearing controlled odd-even effects with suitable nanographene systems is challenging. Here, we demonstrate the successful on-surface synthesis of spin-1/2 antiferromagnetic Heisenberg chains with parity-dependent magnetization based on antiaromatic diaza-hexa-peri-hexabenzocoronene (diaza-HBC) units. Using distinct synthetic strategies, two types of spin chains with different terminals were synthesized, both exhibiting a robust odd-even effect on the spin coupling along the chain. Combined investigations using scanning tunneling microscopy, non-contact atomic force microscopy, density functional theory calculations, and quantum spin models confirmed the structures of the diaza-HBC chains and revealed their magnetic properties, which has an S = 1/2 spin per unit through electron donation from the diaza-HBC core to the Au(111) substrate. Gapped excitations were observed in even-numbered chains, while enhanced Kondo resonance emerged in odd-numbered units of odd-numbered chains due to the redistribution of the unpaired spin along the chain. Our findings provide an effective strategy to construct nanographene spin chains and unveil the odd-even effect in their magnetic properties, offering potential applications in nanoscale spintronics.