Addressing the magnetic properties of sub-monolayers of single-molecule magnets by X-ray magnetic circular dichroism.

We report on a comparative study of electronic and magnetic properties of Mn-6 single-molecule magnets (SMMs) grafted on gold surface. Two derivatives with spin-ground states S = 4 and S = 12 have been functionalized with 3-tp-CO2- (3-thiophene carboxylate, tpc) ligands and characterized as thick films (TFs) as well as sub-monolayers (sMLs) by synchrotron based techniques. X-ray absorption spectroscopy at the Mn L-2.3 edges shows the modification of the spectral lineshape in the sMLs with respect to the TFs suggesting that the local symmetry at the Mn sites changes once the molecules are deposited on gold surface. In spite of this, the expected Mn-III oxidation state is preserved. X-ray magnetic circular dichroism (XMCD) spectra show that the total magnetic moment is only given by spin part because of the quenched orbital moment. Moreover, variable temperature and variable field XMCD spectra reveal an effective decrease of the Mn spin moment for both derivatives.