上海交通大学王世勇研究团队合成了表面无金属卟啉链中的量子纳米磁铁。相关研究成果于2022年10月24日发表在《自然—化学》。

与经典自旋不同，量子磁体是通过交换相互作用相互作用的自旋系统，表现出集体量子行为，如分数激发。分子磁性通常来源于d/f过渡金属，但它们的自旋-轨道耦合和晶体场导致了显著的磁各向异性，破坏了量子自旋的旋转对称性。因此，在无金属体系中构建量子纳米磁体具有重要意义。

该文中，研究人员合成了基于无金属多卟啉体系的单个量子纳米磁体。首先在超高真空下在Au（111）上制备2至5个卟啉的共价链，然后使用扫描隧道显微镜的尖端从选定的碳中除去氢原子。特定卟啉单元向其自由基或双自由基状态的转化使得卟啉内和卟啉间的磁耦合得以调谐。所得链的集体磁性质的表征表明，所构建的S＝1/2反铁磁体显示出间隙激发，而S＝1反铁磁体在偶数和奇数自旋链之间显示出不同的端态，这与海森堡模型计算一致。

附：英文原文

Title: Quantum nanomagnets in on-surface metal-free porphyrin chains

Author: Zhao, Yan, Jiang, Kaiyue, Li, Can, Liu, Yufeng, Zhu, Gucheng, Pizzochero, Michele, Kaxiras, Efthimios, Guan, Dandan, Li, Yaoyi, Zheng, Hao, Liu, Canhua, Jia, Jinfeng, Qin, Mingpu, Zhuang, Xiaodong, Wang, Shiyong

Issue&Volume: 2022-10-24

Abstract: Unlike classic spins, quantum magnets are spin systems that interact via the exchange interaction and exhibit collective quantum behaviours, such as fractional excitations. Molecular magnetism often stems from d/f-transition metals, but their spin–orbit coupling and crystal field induce a significant magnetic anisotropy, breaking the rotation symmetry of quantum spins. Thus, it is of great importance to build quantum nanomagnets in metal-free systems. Here we have synthesized individual quantum nanomagnets based on metal-free multi-porphyrin systems. Covalent chains of two to five porphyrins were first prepared on Au(111) under ultrahigh vacuum, and hydrogen atoms were then removed from selected carbons using the tip of a scanning tunnelling microscope. The conversion of specific porphyrin units to their radical or biradical state enabled the tuning of intra- and inter-porphyrin magnetic coupling. Characterization of the collective magnetic properties of the resulting chains showed that the constructed S=1/2 antiferromagnets display a gapped excitation, whereas the S=1 antiferromagnets exhibit distinct end states between even- and odd-numbered spin chains, consistent with Heisenberg model calculations.

DOI: 10.1038/s41557-022-01061-5

Source: https://www.nature.com/articles/s41557-022-01061-5