Rastertunnelmikroskopie wurde zur Detektion von individuellen Einzelmolekülmagneten auf Goldsubstraten eingesetzt (siehe schematische Formel). Das Adsorbat, [Mn12O12(L)16(H2O)4], wurde durch Abscheidung eines abgeschirmten Dodecamangan(III,IV)‐Clusters aus verdünnten Lösungen in THF/H2O/NH4OH erhalten. Das System kann als erste Stufe hin zu Informationsspeichern mit ultrahoher Speicherdichte auf der Grundlage von Einzelmolekülmagneten angesehen werden.

The incorporation of thioether groups in the structure of a Mn12 single-molecule magnet, [Mn12(O12)(L)16(H2O)4] with L = 4-(methylthio)benzoate, is a successful route to the deposition of well-separated clusters on native gold surfaces and to the addressing of individual molecules by scanning tunnelling microscopy.

The low temperature spin dynamics of a Fe8 Single-Molecule Magnet was studied under circularly polarized electromagnetic radiation allowing us to establish clearly photon-assisted tunneling. This effect, while linear at low power, becomes highly non-linear above a relatively low power threshold. This non-linearity is attributed to the nature of the coupling of the sample to the thermostat. These results are of great importance if such systems are to be used as quantum computers.PACS numbers: PACS numbers: 75.45.+j, 75.60.Ej Molecular nanomagnets have attracted much interest in recent years both from experimental and theoretical point of view [1,2,3,4,5,6,7,8,9,10,11,12,13]. These systems are organometallic clusters characterized by a large spin ground state with a predominant uniaxial anisotropy. These features yield a pronounced barrier for magnetization reversal and therefore a hysteretic behavior below a blocking temperature. The quantum nature of these system makes them very appealing for phenomena occurring on the mesoscopic scale, i.e. at the boundary between classical and quantum physics. Up to now the most thoroughly investigated systems were a dodecanuclear mixed-valence manganese-oxo cluster with acetate ligands (hereafter Mn 12 -ac) [1] and an octanuclear iron(III) oxo-hydroxo cluster of formula [Fe 8 O 2 (OH) 12 (tacn) 6 ] 8+ where tacn is a macrocyclic ligand, (hereafter Fe 8 ) [2], both having a ground spin state S = 10, but substantially differing in their anisotropy. Indeed, while the first is essentially tetragonal with a barrier of 67 K, the latter is orthorhombic with a barrier of 25 K, leading to an enhancement of the ground-state tunneling rate compared to Mn 12 -ac.Recently it has also been proposed that molecular nanomagnets could be used as quantum computers by implementing Grovers algorithm [14]. For this to occur it is necessary to be able to generate an arbitrary superpositions of eigenstates of these systems. The suggested way to do this was through the use of multifrequency coherent magnetic radiation in the microwave and radiofrequency range. This would first introduce and amplify the desired phase for each M state and this information could be finally read-out by standard magnetic resonance techniques. In this approach advantage is taken from the non-equidistance of the M levels of the ground multiplet arising from the large axial anisotropy of these systems, which allows coherent populations of the different M levels. A recent theoretical work pointed out that a very accurate control of pulse shape technique, both in amplitude, duration and choice of frequency is needed to fulfill the condition to design quantum computing devices in -10 -5 0 5 10 Energy quantum number M DM = +1 hω tunneling hω DM = -1 H = 0 FIG. 1: Schematic representation of photon assisted tunneling. On irradiating a Fe8 sample with a radiation of wavelength corresponding to the M = -10 to -9 splitting (vertical arrow), an enhancement of the fraction of molecules that tunnel from the first excited state is exp...