Citation for published version (APA):Paul, M., Sing, M., Claessen, R., Schrupp, D., & Brabers, V. A. M. (2007). Thermodynamic stability and atomic and electronic structure of reduced Fe3 O4 (111) Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nl providing details and we will investigate your claim. Magnetite ͑111͒ single-crystal surfaces prepared in situ under different reducing conditions and-as a result-with varying stoichiometries have been studied by scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoemission spectroscopy. The coexistence of several surface structures has been detected, indicating only small differences in their relative stabilities. In particular, an unusual previously unreported superstructure has been found for a strongly reduced surface. Its microscopic origin is discussed against the background of recent results from scanning tunneling microscopy of the oxidized magnetite ͑111͒ surface and from ab initio thermodynamics. Partly at variance with and partly complementary to these results, we regard as driving force elastic strain due to the lateral mismatch between Fe 3 O 4 substrate and Fe 1−x O-like overlayer.

The quasiparticle dynamics of electrons in a magnetically ordered state is investigated by high-resolution angle-resolved photoemission of Ni(110) at 10 K. The self-energy is extracted for high binding energies reaching up to 500 meV, using a Gutzwiller calculation as a reference frame for correlated quasiparticles. Significant deviations exist in the 300 meV range, as identified on magnetic bulk bands for the first time. The discrepancy is strikingly well described by a self-energy model assuming interactions with spin excitations. Implications relating to different electron-electron correlation regimes are discussed. PACS numbers:The many-body ground state of condensed matter is reflected in its single-particle excitations, which in many cases are significantly modified by coupling to collective modes. Such interactions lead to a pronounced change in the quasiparticle (QP) band dispersion, a so-called kink. In metals, the kink from electron-phonon coupling is well-established [1]. Energy-renormalization is also found in the high-T c cuprates [2]. However, the nature of this feature is not yet completely clarified, albeit of primordial importance to the mechanism of superconductivity. It is being discussed whether the kink is derived from coupling to phonons or to spin fluctuations [3]. Their similar energy scales in the cuprates make it difficult to separate the contributions. Recent experiments on relationships with sample parameters [4,5] argue for the magnetic coupling model. Closer resemblance to magnetic metals is found in the newly discovered iron-based pnictides [6]. Their parent compounds are true metals with delocalized electrons forming an antiferromagnetic spin density wave. A pairing mechanism based on spin fluctuations has been suggested [7].Interestingly, a different explanation for kinks in strongly correlated electron systems was suggested recently, which does not require electron-boson coupling. Calculations based on pure electron-electron interaction found two well-separated regimes of QP renormalization [8]. Near the Fermi level, well-defined QPs exist according to Fermi liquid theory. Beyond a characteristic energy scale, the slope of the electronic self-energy changes abruptly, resulting in reduced QP lifetimes and energy renormalization. In the transition between these situations, a dispersion anomaly is expected to emerge [8].In order to gain access to these many-body interactions, a three-dimensional Fermi liquid in the ferromagnetic state seems a suitable model system. The energy scales for the lattice and spin wave excitations in typical ferromagnets such as Ni differ by approximately an order of magnitude, and hence will affect the QPs at different binding energies [9,10]. Furthermore, it is established that the valence band states are strongly correlated [11,12], which is proven by a concomitant photoemission satellite. This allows to directly adress the interplay of correlation physics and QP formation in the presence of distinct spin excitations.In this Letter, we present a high-r...

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We demonstrate the epitaxial growth of Fe 3 O 4 films on ZnO by a simple reactive deposition procedure using molecular oxygen as an oxidizing agent. X-ray photoelectron spectroscopy results evidence that the iron-oxide surface is nearly stoichiometric magnetite. X-ray diffraction results indicate monocrystalline epitaxy and almost complete structural relaxation. Scanning transmission electron micrographs reveal that the microstructure consists of domains which are separated by antiphase boundaries or twin boundaries. The magnetite films show rather slow magnetization behavior in comparison with bulk crystals probably due to reduced magnetization at antiphase boundaries in small applied fields.

Magnetite ͑Fe 3 O 4 ͒ thin films on GaAs have been studied with hard x-ray photoelectron spectroscopy ͑HAXPES͒ and low-energy electron diffraction. Films prepared under different growth conditions are compared with respect to stoichiometry, oxidation, and chemical nature. Employing the considerably enhanced probing depth of HAXPES as compared to conventional x-ray photoelectron spectroscopy allows us to investigate the chemical state of the film-substrate interfaces. The degree of oxidation and intermixing at the interface are dependent on the applied growth conditions; in particular, we found that metallic Fe, As 2 O 3 , and Ga 2 O 3 exist at the interface. These interface phases might be detrimental for spin injection from magnetite into GaAs.