Electronic structure of Mn12 complexes grafted on Au(111) Surface
Fonin, Mikhail; Voss, Soenke; Burgert, Michael; Dedkov, Yury S.; Groth, Ulrich; Ruediger, Ulrich
Germany

In recent years, single molecule magnets (SMMs) have attracted much attention due to their unique properties such as quantum tunneling of magnetization (QTM) and hysteresis of pure molecular origin [1]. The most widely investigated class of SMMs is the Mn12-group, comprised of Mn12-acetate, the first SMM discovered [1], and its derivatives. The high spin ground state (S=10) of Mn12, combined with large uniaxial magnetic anisotropy, results in an energy barrier for spin reversal, giving rise to superparamagnetic behavior at low temperature. In the range of 2 K the magnetization relaxation becomes extremely slow, and each molecule behaves like a classical magnet with a magnetic moment of 20 μB. Up to date, experiments on Mn12 have been performed exclusively on bulklike material while the magnetic as well as the electronic properties of the individual molecules or SMM monolayers on a surface remain to large extent unknown.
In the present work electronic properties of monolayers of Mn12-complexes chemically grafted on the Au(111) surface have been studied in detail by means of near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and photoemission spectroscopy (PES) as well as scanning tunneling microscopy (STM) and spectroscopy (STS). NEXFS measurements reveal a significant deviation of spectra obtained from molecular monolayers from those obtained from single crystals indicating a partial fragmentation of the Mn12-cores on the Au(111) surface. However, a large amount of Mn12-molecules seems to retain their structural integrity upon surface deposition by using an appropriate combination of Mn12 cluster and substrate functionalization [2]. The Mn 3d partial density of states for the occupied states were extracted from the resonant PES spectra of Mn12-complexes [2] whereas the unoccupied states near EF were probed by STS.
[1] D. Gatteschi, R. Sessoli, and J. Villain, Molecular Nanomagnets (Oxford University Press, 2006).
[2] S. Voss, M. Fonin, M. Burgert, U. Groth, U. Rüdiger, and Yu. S. Dedkov, Phys. Rev. B 75, 045102 (2007).
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