Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-based Metal-Organic Networks

The electronic and magnetic properties of Mn coordinated to 1,2,4,S-tetracyanobenzene (TCNB) in Mn-TCNB two-dimensional metal-ligand networks have been investigated by combining scanning tunneling microscopy and X-ray magnetic circular dichroism (XMCD) performed at low temperature (3 K). When formed on Au(111) and Ag(111) substrates, the Mn-TCNB networks display similar geometric structures. Magnetization curves reveal ferromagnetic coupling of the Mn sites with similar single-ion anisotropy energies but different coupling constants. Low-temperature XMCD spectra show that the local environment of the Mn centers differs appreciably for the two substrates. Multiplet structure calculations were used to derive the corresponding ligand field parameters, confirming an in-plane uniaxial anisotropy. The observed interatomic coupling is discussed in terms of superexchange as well as substrate-mediated magnetic interactions.