Control of spin liquid-like dynamics by geometry of 2D nanocluster networks

Abstract

Network structures of magnetic molecular assemblies on a two-dimensional (2D) material are attractive platforms for molecular spintronics and for the study of 2D magnetic materials. However, it is still a challenging task to connect such assemblies with appropriate magnetic interactions. Recently, uniform nanoclusters consisting of about 100 magnetic amino-ferrocene molecules were self-organized on a graphene oxide nanosheet by on-surface synthesis. Here, the dynamics of weakly interacting molecular spins in the nanocluster networks is investigated by exploiting the tunability of the intercluster distance through the chemical reaction. The stochastic simulation shows that the entanglement of the spin orientations at the sites in the nanocluster by magnetic dipole interactions leads to a liquid-like behavior of the spins (S = 5/2) at T ≲ 15 K, generating spin correlations and slow dynamics observed in Mössbauer spectroscopy and magnetic susceptibility. The energy barrier for generating magnetic relaxation and the deviation temperature from classical, thermally activated relaxation depend on the intercluster distance, i.e., the magnetic interactions between the nanoclusters, indicating that the relaxation can be tuned by the geometry of the nanocluster networks. The present results pave the way for the chemical design of 2D nanocluster networks and chemically functionalized 2D materials.