  The electronic and magnetic properties of Mn coordinated to
1,2,4,5-tetracyanobenzene (TCNB) in the Mn-TCNB 2D 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 (FM) 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.
