Competing Intramolecular Superexchange Interactions in the CuFe4 Metallacrown on Au(111)An Inelastic Tunneling Spectroscopy Study

Spin-flip inelastic tunneling spectroscopy (SF-IETS) at low temperatures allows the electrical characterization of surface magnetism, particularly for molecule/substrate systems which can be interesting for molecular spintronics. Here, SF-IETS was used to explore the competing character of intramolecular superexchange interactions on a device-compatible metallic substrate. For this purpose, the multinuclear metallacrown system CuFe4, [Cu­(ii)­(DMF)2Cl2[12-MCFe(III)N(Shi)-4]­(DMF)4·2DMF], on Au(111) and its resulting “surface” spin ground state were studied. After the deposition of CuFe4 molecules by a solution-based technique onto a Au(111) surface, the CuFe4 system exhibits an evident hallmark of inelastic tunneling, that is, step-like features on the differential conductance spectra, which we attribute to spin-flip excitations. By analyzing the experimental curve with a second-order electron transport model simulation, we determined the exchange coupling constants and the spin ground state. Our results are compared with those spin ground states published in the literature for this compound based on the broken-symmetry density functional theory calculations and temperature-dependent magnetic susceptibility measurements.