Engineering Ferrimagnetic Interactions in Molecular Quantum Systems

TL;DR

This paper reports the synthesis and characterization of heterospin-coupling motifs in organic molecules, demonstrating tunable ferrimagnetic interactions and complex spin states relevant for quantum technologies.

Contribution

It introduces a synthetic strategy for creating heterospin molecules with well-defined magnetic properties and validates the Heisenberg model for describing their magnetic behavior.

Findings

Successfully synthesized heterospin molecules with ferrimagnetic order.

Resolved magnetic excitations using inelastic electron tunneling spectroscopy.

Demonstrated complex spin configurations including $S=0$ and $S=3/2$ ground states.

Abstract

Achieving long-range ferrimagnetic order in purely organic systems remains a major challenge in molecular magnetism. Here we report the synthesis and characterization of heterospin-coupling motifs, formed by covalently linking spin-1/2 and spin-1 triangular nanographenes. A combined solution-phase and on-surface synthetic strategy yields three distinct compounds, whose structures are elucidated by bond-resolved scanning probe microscopy. Starting from a spin-1/2--spin-1 dimer as the elemental ferrimagnetic unit, we employ inelastic electron tunneling spectroscopy to resolve low-energy magnetic excitations and extract the parameters of the Heisenberg Hamiltonian. Extension to trimeric architectures results in two distinct spin configurations, with compensated ($S=0$) and uncompensated ($S=3/2$) ferrimagnetic ground states. The Heisenberg model accurately describes all magnetic transitions, offering direct insight into increasingly complex spin Hamiltonians. These findings establish a molecular platform for designing tunable heterospin systems with robust exchange interactions, opening routes toward multi-level spin encoding in qudit-based quantum technologies.