Molecular-Scale Memory Generated by Liquid-Like Spins in On-Surface Synthesized Nanoclusters

Memory is the functional ability to store, access, and erase signatures of past history. How materials can form a memory has stimulated intellectual curiosity in various fields of research. Here, the memory function and slow dynamics are investigated by exploiting liquid-like molecular spins in the equilibrium or nonequilibrium states in amino-ferrocene nanoclusters with an average diameter of about 2 nm. The fluidly entangled structures of spin orientations at the molecular sites in the nanocluster are formed by their magnetic dipole interactions at low temperatures under zero or constant magnetic field, generating slow dynamics that behave like a liquid in equilibrium, although slow dynamics are generally considered to be nonequilibrium phenomena. Removing the applied field from the liquid-like spins creates frozen entangled structures in nonequilibrium that exhibit a memory function by detaching and reattaching a molecular spin from the entangled structure through a thermal activation barrier. This form of molecular memory does not use magnetic anisotropy and is completely different from conventional molecular memories based on changes of molecular structure and charge.