Wide Tuning of Magnetic Exchange Coupling in Nanographenes through Orbital-Symmetry Engineering

Abstract

Open-shell nanographenes appear as promising candidates for future applications in spintronics and quantum technologies. How to engineer and obtain large magnetic exchange coupling in nanographenes is crucial for realizing their applications at room temperature. Here, we reveal a mechanism of engineering magnetic exchange coupling in nanographenes through tailoring their frontier orbital symmetries, investigated by combining scanning probe microscope measurements and different levels of theoretical calculations. In nanographenes of phenalenyl spin dimers, their exchange interaction can be widely tuned from 20 meV to 160 meV. Theoretical calculations reveal that frontier orbital symmetries play a key role in engineering magnetic exchange coupling on such a large scale. Moreover, a spin trimer is demonstrated for investigating the magnetic interaction among three spins with unequal magnetic exchange coupling, in agreement with Heisenberg spin chain model calculations. Our results provide insights into both theoretical design and experimental realization of nanographene materials with widely tunable exchange interactions, potentially useful for realizing magnetically operable graphene nanomaterials.

Magnetic Coupling Control in Triangulene Dimers

“…Therefore, a different number of sites in the sublattices is crucial to achieve molecules with high-spin ground states. 25,26 One promising strategy involves the utilization of meta-connected phenyl rings. 10,27−29 However, introducing heteroatoms, such as O, N, and B, can break the condition of Lieb's theorem and thus go beyond the predictive capabilities of Ovchinnikov's rule.…”

“…The total spin of the system emerges from half-filling of the degenerate highest occupied molecular orbitals (HOMOs) according to Hund’s rule, and the multiplicity is given by S = ( N A – N B )/2, where N A and N B are the numbers of sites belonging to the two honeycomb sublattices. Therefore, a different number of sites in the sublattices is crucial to achieve molecules with high-spin ground states. , One promising strategy involves the utilization of meta-connected phenyl rings. ,− However, introducing heteroatoms, such as O, N, and B, can break the condition of Lieb’s theorem and thus go beyond the predictive capabilities of Ovchinnikov’s rule. This may open doors for realizing unconventional metal-free magnetism.…”