Fermi surface and electronic structure of Pb/Ge(111)

The electronic structure of Pb/Ge(111) has been probed along the temperature-induced phase transition ct -root 3X root 3R30 degrees double right arrow 3 X 3 using angle-resolved photoemission. The alpha-root 3X root 3R30 degrees phase is metallic due to the existence of a half-filled, dispersing surface band. The 3 X 3 phase is characterized by the appearance of an additional surface band with 3 X 3 periodicity, whose role in the phase transition is discussed. The Fermi-surface topology of the alpha-root 3X root 3R30 degrees phase has been probed using angle-resolved photoemission. Its shape is undulated, and it resembles strongly the theoretical prediction, with a Fermi momentum of 0.31 Angstrom(-1) along directions and 0.40 Angstrom(-1) along directions. These values were determined from different experimental methods, and agree with the values needed for a perfect 3 X 3 nesting. However, the Fermi surface exhibits no large flat areas suitable for electronic nesting

Control of magnetic properties of FeCo thin films grown by sputtering

Control of magnetic properties of FeCo thin films grown by sputterin

Effect of photoelectron mean free path on the photoemission cross-section of Cu(111) and Ag(111) Shockley states

The photoemission cross-section of Shockley states of Cu(111) and Ag(111) surfaces is studied over a wide range of photon energies. The constant initial-state spectra are very different for the two surfaces and show rich structure that does not follow the generally accepted nearly free electron model for the final state. Angle resolved photoemission data are interpreted within a one-step ab initio theory, revealing a multiple Bloch wave structure of photoemission final states. The inelastic scattering parameter-optical potential-is determined, and the energy dependence of the mean free path of the outgoing electron is calculated, which turns out to be the key for the understanding of the photoemission cross-section curve. These are essential steps for future exploration of wave function perturbations in the presence of surface nanostructures. 2011 American Physical Society.This work was supported by the Spanish Ministerio de Ciencia e Innovación (Grants No. FIS2010-19609-C02-02, FIS2008-00399, MAT2010-21156-C03-01, and MAT2010-21156-C03-02 and through the Research Program Ramón y Cajal) and the Basque Government (IT-257-07). The SRC is funded by the National Science Foundation (Award No. DMR-0084402).Peer Reviewe

Origin of the surface metallization in single-domain K/Si(100)2x1

The electronic structure and the metallization onset of single-domain K/Si(100)2x1 have been investigated with angle-resolved polarization-sensitive ultraviolet photoemission. The electronic states producing the surface metallization have been studied for increasing K coverages up to room-temperature saturation. As K coverage increases, the interface undergoes a transition at a critical coverage, from a low-coverage semiconducting phase, to a saturation-coverage metallic phase. Two different surface states (F-1 and F-2) have been detected in the vicinity of the Fermi level. These two states are sequentially filled along the metallization process. The coverage dependence of both F-1 and F-2, and their symmetry properties indicate that the metallization is due to the filling of an initially empty surface band (appearance of F-2) We relate F-1 to the completion of K chains in the single-domain surface. The changes detected in K 3p line shape correlate well with the modifications of the valence band, and support that the surface remains semiconducting up to the filling of F-2

Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)

Imaging the change in the magnetization vector in real time by spin-polarized low-energy electron microscopy, we observed a hydrogen-induced, reversible spin-reorientation transition in a cobalt bilayer on Ru(0001). Initially, hydrogen sorption reduces the size of out-of-plane magnetic domains and leads to the formation of a magnetic stripe domain pattern, which can be understood as a consequence of reducing the out-of-plane magnetic anisotropy. Further hydrogen sorption induces a transition to an in-plane easy-axis. Desorbing the hydrogen by heating the film to 400 K recovers the original out-of-plane magnetization. By means of ab-initio calculations we determine that the origin of the transition is the local effect of the hybridization of the hydrogen orbital and the orbitals of the Co atoms bonded to the absorbed hydrogen.Comment: 5 figure

Valence band circular dichroism in non-magnetic Ag/Ru(0001) at normal emission

For the non-magnetic system of Ag films on Ru(0001), we have measured the circular dichroism of photoelectrons emitted along the surface normal, the geometry typically used in photoemission electron microscopy. Photoemission spectra were acquired from micrometer-sized regions having uniformly thick Ag films on a single, atomically flat Ru terrace. For a single Ag layer, we find a circular dichroism that exceeds 6% at the d-derived band region around 4.5eV binding energy. The dichroism decreases as the Ag film thickness increases to three atomic layers. We discuss the origin of the circular dichroism in terms of the symmetry lowering that can occur even in normal emission. © 2011 IOP Publishing Ltd.Peer Reviewe

Memory effect and magnetocrystalline anisotropy impact on the surface magnetic domains of magnetite(001)

The structure of magnetic domains, i.e. regions of uniform magnetization separated by domain walls, depends on the balance of competing interactions present in ferromagnetic (or ferrimagnetic) materials. When these interactions change then domain configurations also change as a result. Magnetite provides a good test bench to study these effects, as its magnetocrystalline anisotropy varies significantly with temperature. Using spin-polarized electron microscopy to map the micromagnetic domain structure in the (001) surface of a macroscopic magnetite crystal (similar to 1 cm size) shows complex domain patterns with characteristic length-scales in the micrometer range and highly temperature dependent domain geometries. Although heating above the Curie temperature erases the domain patterns completely, cooling down reproduces domain patterns not only in terms of general characteristics: instead, complex microscopic domain geometries are reproduced in almost perfect fidelity between heating cycles. A possible explanation of the origin of the high-fidelity reproducibility is suggested to be a combination of the presence of hematite inclusions that lock bulk domains, together with the strong effect of the first order magnetocrystalline anisotropy which competes with the shape anisotropy to give rise to the observed complex patterns

Spin reorientation transition of magnetite (001)

We have imaged the rearrangement of the magnetic domains on magnetite (001) when crossing the spin reorientation transition and the Verwey transition with nanometer resolution. By means of spin-polarized low-energy electron microscopy we have monitored the change in the easy axes lowering the temperature through both transitions in remanence. The spin reorientation transition occurs in two steps: initial nucleation and growth of domains with a new surface magnetic orientation is followed by a smooth evolution.We thank Dr. A. T. N'Diaye for his support with the scripts for the color representation of the magnetization. This research was partly supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under Projects No. MAT2011-52477-C5-2-P, No. MAT2012-38045-C04-01, and No. MAT2015-64110-C2-1-P. G.S.P. and R.B. acknowledge funding from the Austrian Science Fund START prize Y 847-N20 and Project No. P24925-N20. Experiments were performed at the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, Scientific User Facilities Division, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231. L.M.-G. thanks the MINECO for an FPI contract with reference Contract No. BES-2013-063396. R.B. acknowledges a stipend from the TU Wien and Austrian Science Fund doctoral college Solids4Fun (Project No. W1243). A.M. thanks the support of the Spanish Ministry of Education through Project No. PRX14/00307.Peer Reviewe