Amtry Stephanie M, Campello Arthur C, Tong Christopher L, Puggioni Danilo S, Rondinelli James M, Lee Young S, Freedman Danna E
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Department of Applied Physics, Stanford University, Stanford, California 94305, United States.
J Am Chem Soc. 2024 Oct 23;146(42):29040-29052. doi: 10.1021/jacs.4c10113. Epub 2024 Oct 9.
Patterning spins to generate collective behavior is at the core of condensed matter physics. Physicists develop techniques, including the fabrication of magnetic nanostructures and precision layering of materials specifically to engender frustrated lattices. As chemists, we can access such exotic materials through targeted chemical synthesis and create new lattice types by chemical design. Here, we introduce a new approach to induce magnetic frustration on a modified honeycomb lattice through a competition of alternating antiferromagnetic (AFM) and ferromagnetic (FM) nearest-neighbor interactions. By subtly modulating these two types of interactions through facile synthetic modifications, we created two systems: (1) a topological spin glass and (2) a frustrated spin-canted magnet with low-temperature exchange bias. To design this unconventional magnetic lattice, we used a metal-organic framework (MOF) platform, Ni(pymca)X (NipymcaX where pymca = pyrimidine-2-carboxylato and X = Cl, Br). We isolated two MOFs, NipymcaCl and NipymcaBr, featuring canted Ni-based moments. Despite this similarity, differences in the single-ion anisotropies of the Ni spins result in distinct magnetic properties for each material. NipymcaCl is a topological spin glass, while NipymcaBr is a rare frustrated magnet with low-temperature exchange bias. Density functional theory calculations and Monte Carlo simulations on the NipymcaX lattice support the presence of magnetic frustration as a result of alternating AFM and FM interactions. Our calculations enabled us to determine the ground-state spin configuration and the distribution of spin-spin correlations relative to paradigmatic kagomé and triangular lattices. This modified honeycomb lattice is similar to the electronic Kekulé-O phase in graphene and provides a highly tunable platform to realize unconventional spin physics.
通过调控自旋来产生集体行为是凝聚态物理的核心。物理学家开发了多种技术，包括制造磁性纳米结构以及对材料进行精确分层，专门用于构建受挫晶格。作为化学家，我们可以通过有针对性的化学合成来获取此类奇特材料，并通过化学设计创造新的晶格类型。在此，我们介绍一种新方法，通过交替的反铁磁（AFM）和铁磁（FM）最近邻相互作用的竞争，在修饰的蜂窝晶格上诱导磁挫折。通过简便的合成修饰巧妙地调节这两种相互作用类型，我们创建了两个系统：（1）拓扑自旋玻璃和（2）具有低温交换偏置的受挫自旋倾斜磁体。为了设计这种非常规磁晶格，我们使用了金属有机框架（MOF）平台Ni(pymca)X（NipymcaX，其中pymca = 嘧啶 - 2 - 羧基，X = Cl，Br）。我们分离出了两种MOF，NipymcaCl和NipymcaBr，它们具有倾斜的镍基磁矩。尽管有这种相似性，但镍自旋的单离子各向异性差异导致每种材料具有不同的磁性。NipymcaCl是一种拓扑自旋玻璃，而NipymcaBr是一种罕见的具有低温交换偏置的受挫磁体。对NipymcaX晶格的密度泛函理论计算和蒙特卡罗模拟支持了由于交替的AFM和FM相互作用而存在磁挫折。我们的计算使我们能够确定基态自旋构型以及相对于典型的 kagomé 和三角形晶格的自旋 - 自旋相关性分布。这种修饰的蜂窝晶格类似于石墨烯中的电子凯库勒 - O相，并提供了一个高度可调谐的平台来实现非常规自旋物理。
