Magnetism of Atomically Precise Gold and Doped Nanoclusters: Delocalized Spin and Interparticle Coupling

Abstract

The magnetic properties of Au nanoparticles (NPs) have long been an intriguing topic in fundamental research. In the quantum size regime (1–3 nm), Au NPs indeed exhibit distinct magnetism in contrast to diamagnetic gold in bulk or relatively large plasmonic NPs. However, previous studies often give controversial results due to imprecise NPs used in magnetic studies, making it difficult to understand the origin of magnetism in Au NPs. Recent progress has led to atomically precise Au nanoclusters (NCs for differentiation with regular NPs), which can serve as a unique model for studying the delocalized spin in isolated NCs and the spin–spin exchange interaction between NCs in assembled solids. Moreover, such mechanisms are correlated to the atomic structures of the magnetic NCs. The precise formulas of the NCs serve as a clear indicator for magnetism. So far, the Au-thiolate NCs reported to be magnetic, including the doped ones, all contain icosahedral kernel structures, which are facile compared to other structures in adding or removing one electron for endowing magnetism to the NCs. Heteroatom doping in the NCs is an effective method to probe the magnetic mechanism in NCs, such as the origin of magnetic anisotropy, and the counterion tailoring for those charged NCs can also impart magnetism to the initially diamagnetic NCs via stabilizing a particular charge state of the NCs. While only a few cases of NCs have been reported with magnetism thus far, future research on metal NCs (especially in the critical regime between molecular and metallic state) will reveal more fundamentals of magnetism, and the control of spin–spin exchange coupling in nanocluster-assembled solids is particularly promising for tailoring the magnetic functionality of NCs and ultimately finding versatile applications.