The magnetic properties of carbon materials are at present the focus of intense research effort in physics, chemistry and materials science due to their potential applications in spintronics and quantum computing. Although the presence of spins in open-shell nanographenes has recently been confirmed, the ability to control magnetic coupling sign has remained elusive but highly desirable. Here, we demonstrate an effective approach of engineering magnetic ground states in atomically precise open-shell bipartite/nonbipartite nanographenes using combined scanning probe techniques and mean-field Hubbard model calculations. The magnetic coupling sign between two spins was controlled via breaking bipartite lattice symmetry of nanographenes. In addition, the exchange-interaction strength between two spins has been widely tuned by finely tailoring their spin density overlap, realizing a large exchange-interaction strength of 42 meV. Our demonstrated method provides ample opportunities for designer above-room-temperature magnetic phases and functionalities in graphene nanomaterials.

由于碳材料的磁性能在自旋电子学和量子计算中的潜在应用，目前已成为物理学，化学和材料科学领域广泛研究的重点。尽管最近已证实在开壳纳米石墨烯中存在自旋，但是控制磁耦合符号的能力仍然难以捉摸，但是非常需要。在这里，我们展示了一种有效的方法，可通过结合使用扫描探针技术和均场哈伯德模型计算，在原子精确的开壳二分体/非二分体纳米石墨烯中工程化磁性基态。通过破坏纳米石墨烯的二方晶格对称性来控制两个自旋之间的磁耦合符号。此外，通过自定义两个自旋密度重叠，可以广泛调节两个自旋之间的交换相互作用强度，从而实现42 meV的大交换相互作用强度。我们证明的方法为石墨烯纳米材料中的设计者提供了高于室温的磁性相和功能的充足机会。