An Experimental Study of Mn12-Family Molecular Magnets in Isolation with High Spatial Resolution

Abstract

I report my studies of Mn12O12(C6H5COO)16(H2O)4, which will be referred to as Mn12-Ph, a single molecule magnet, on Cu(111) and HOPG (highly oriented pyrolytic graphite) surfaces by scanning tunneling microscopy (STM). A technique of vacuum spray injection for room temperature deposition of films of a tunable density, between very diffuse isolated molecules and complete surface coverage, onto sample substrates was developed and used to create sub-monolayer films of Mn12-Ph on Cu(111) for low temperature observation. Scanning tunneling spectroscopy (STS) of samples at low temperatures produced insights into the local density of states (LDOS) with a high degree of precision with spatial location (X,Y,Z) and energy (eV).These spectroscopic data were analyzed and compared to results in the literature from competing groups. A theoretical model of spinstability in an interacting graph of spins was developed and simulations were carried out to find a weak topological invariant to perturbation of a given spinstate for a class of ferromagnetically interacting spingraphs. A phenomenological (post hoc) model built upon poor coupling between the molecule's wave function and the Cu surface wave function is proposed to explain the spectroscopic data. Normalized (to the Cu background) junction impedance is calculated and compared in different regions of the molecular interior to form a better view of the evolution of the tunnel junction current with respect to applied bias voltage.