Matthias Muntwiler

An endohedral single-molecule magnet with long relaxation times: DySc2N@C80.

The magnetism of DySc(2)N@C(80) endofullerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temperatures of 2 K and in fields up to 7 T. XMCD shows hysteresis of the 4f spin and orbital moment in Dy(III) ions. SQUID magnetometry indicates hysteresis below 6 K, while thermal and nonthermal relaxation is observed. Dilution of DySc(2)N@C(80) samples with C(60) increases the zero-field 4f electron relaxation time at 2 K to several hours.

Spin-polarized Fermi surface mapping

Abstract The magnetic and electronic properties of itinerant ferromagnets and their interplay have been studied in the last few years by spin resolved electron spectroscopy on one hand and by high-resolution angle-resolved photoemission experiments on the other. We discuss how the two approaches can be combined in a high resolution electron spectrometer with spin resolution for angle-scanned Fermi surface mapping experiments. We have built this new instrument, which allows an advance into a deeper understanding of magnetic thin film or multilayer systems, where band structures become intricately dense in momentum space and where the magnetization direction can change from layer to layer. Spin-resolution is thus required to arrive at a correct assignment of spectral features. A fully three-dimensional polarimeter makes the instrument ‘complete’ in the sense that all properties of the photoelectron are measured. First experiments on Ni(111) conclusively confirm previous band and spin assignments at the Fermi level and demonstrate the correct functioning of the apparatus.

Tunneling, remanence, and frustration in dysprosium-based endohedral single-molecule magnets

Paramagnetic atoms inside nanometer sized fullerenes realize robust, and chemically protected, spin systems. Changing the stoichiometry of the endohedral clusters results in a variety of magnetic ground states, as it is demonstrated for DynSc3-nN@C-80 (n = 1,2,3). All three exhibit distinct hysteresis and qualify as single-molecule magnets. In zero field the magnetization of n = 1 decays via quantum tunneling, while ferromagnetic coupling of the individual dysprosium moments results in remanence for Dy2ScN@C-80 and in a frustrated ground state for n = 3. The latter ground state turns out to be one of the simplest realizations of a frustrated, ferromagnetically coupled, system.

Surface Aligned Magnetic Moments and Hysteresis of an Endohedral Single-Molecule Magnet on a Metal

The interaction between the endohedral unit in the single-molecule magnet Dy_{2}ScN@C_{80} and a rhodium (111) substrate leads to alignment of the Dy 4f orbitals. The resulting orientation of the Dy_{2}ScN plane parallel to the surface is inferred from comparison of the angular anisotropy of x-ray absorption spectra and multiplet calculations in the corresponding ligand field. The x-ray magnetic circular dichroism is also angle dependent and signals strong magnetocrystalline anisotropy. This directly relates geometric and magnetic structure. Element specific magnetization curves from different coverages exhibit hysteresis at a sample temperature of ∼4  K. From the measured hysteresis curves, we estimate the zero field remanence lifetime during x-ray exposure of a submonolayer to be about 30 seconds.

Rocking-motion-induced charging of C60 on h-BN/Ni(111)

One monolayer Of C-60 on one monolayer of hexagonal boron nitride on nickel is investigated by photoemission. Between 150 and 250 K the work function decreases and the binding energy of the highest-occupied molecular orbital increases by \A 100 meV. In parallel, the occupancy of the-in the cold state almost empty-lowest unoccupied molecular orbital (LUMO) changes by 0.4\P 0.1 electrons. This charge redistribution is triggered by the onset of molecular rocking motion, i.e., by orientation dependent tunneling between the LUMO Of C-60 and the substrate. The magnitude of the charge transfer is large and cannot be explained within a single-particle picture. It is proposed to involve electron-phonon coupling where C-60(-) polaron formation leads to electron self-trapping.

The electronic structure of a surfactant layer: Pb/Cu(1 1 1)

The electronic structure of an incommensurate Pb layer on Cu(1 1 1) is investigated by means of angle scanned ultraviolet photoemission. Despite of the rather complex atomic structure with three competing periodicities, we observe a well defined band structure, reflecting essentially the fundamental (1 1)-periodicity of the adlayer. Comparison with band structure calculations for a free standing Pb-layer shows that all observed bands can be fully attributed to the overlayer. 2003 Elsevier Science B.V. All rights reserved.

Surface science at the PEARL beamline of the Swiss Light Source

The Photo-Emission and Atomic Resolution Laboratory is a new soft X-ray beamline at the Swiss Light Source for the study of surface structure using photoelectron diffraction and scanning tunneling microscopy.

Excited states at interfaces of a metal-supported ultrathin oxide film

We report layer-resolved measurements of the \textit{unoccupied} electronic structure of ultrathin MgO films grown on Ag(001). The metal-induced gap states at the metal/oxide interface, the oxide band gap as well as a surface core exciton involving an image-potential state of the vacuum are revealed through resonant Auger spectroscopy of the Mg

Thermally induced anchoring of a zinc-carboxyphenylporphyrin on rutile TiO2 (110)

KL_{23}L_{23}

On-Surface Growth Dynamics of Graphene Nanoribbons: The Role of Halogen Functionalization

Auger transition. Our results demonstrate how to obtain new insights on \textit{empty} states at interfaces of metal-supported ultrathin oxide films.