Chemistry-dependent magnetic properties at the FeNi oxide–metal interface

Fe and Ni compounds and their oxides offer stoichiometry dependent magnetic properties, exploitable for the design of magnetic heterojunctions

Growth and electronic and magnetic structure of iron oxide films on Pt(111)

Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111) single crystal either by the reactive deposition of iron or oxidation of metallic iron monolayers. These films were characterized using low energy electron diffraction, scanning tunneling microscopy and conversion electron Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth of Fe3O4, in which the electronic and magnetic properties of the bulk material were modulated by superparamagnetic size effects for thicknesses below 2 nm, revealing specific surface and interface features. In contrast, the oxide films with FeO stoichiometry, which could be stabilized as thick as 4 nm under special preparation conditions, had electronic and magnetic properties that were very different from their bulk counterpart, w\"ustite. Unusual long range magnetic order appeared at room temperature for thicknesses between three and ten monolayers, the appearance of which requires severe structural modification from the rock-salt structure.Comment: 17 pages, 6 figures, 50 reference

Fe3O4(001) films on Fe(001): Termination and reconstruction of iron-rich surfaces

High-quality and impurity-free magnetite surfaces with (sqrt2xsqrt2)R45o reconstruction have been obtained for the Fe3O4(001) epitaxial films deposited on Fe(001). Based on atomically resolved STM images for both negative and positive sample polarity and Density Functional Theory calculations, a model of the magnetite (001) surface terminated with Fe ions forming dimers on the reconstructed (sqrt2xsqrt2)R45o octahedral iron layer is proposed.Comment: 17 pages 4 figure

The effect of ultrafine WO3 nanoparticles on the organization of thylakoids enriched in photosystem II and energy transfer in photosystem II complexes

In this work, a new approach to construct self-assembled hybrid systems based on natural PSII-enriched thylakoid membranes (PSII BBY) is demonstrated. Superfine m-WO3 NPs (≈1–2 nm) are introduced into PSII BBY. Transmission electron microscopy (TEM) measurements showed that even the highest concentrations of NPs used did not degrade the PSII BBY membranes. Using atomic force microscopy (AFM), it is shown that the organization of PSII BBY depends strongly on the concentration of NPs applied. This proved that the superfine NPs can easily penetrate the thylakoid membrane and interact with its components. These changes are also related to the modified energy transfer between the external light-harvesting antennas and the PSII reaction center, shown by absorption and fluorescence experiments. The biohybrid system shows stability at pH 6.5, the native operating environment of PSII, so a high rate of O2 evolution is expected. In addition, the light-induced water-splitting process can be further stimulated by the direct interaction of superfine WO3 NPs with the donor and acceptor sides of PSII. The water-splitting activity and stability of this colloidal system are under investigation

From Monoatomic Multilayers To Ordered Alloys

Recent progress in UHV preparation and characterization methods resulted in a large variety of novel materials. Among them, magnetic multilayers have become one of the mostly investigated system due to interesting phenomena like oscillating indirect exchange coupling, spin dependent electron transport, or large perpendicular anisotropies. An attractive possibility given by the molecular beam epitaxy is to grow the multilayer structures on atomic scale by the so-called atomic layer deposition. At the low thickness limit, a multilayer structure, in which few atomic layers of different metals are stacked alternately, is expected to be an artificial ordered alloy. Such artificial material, which does not exist in the equilibrium bulk phase, was constructed for the first time as the AuFe ordered alloy of the L1$\text{}_{0}$ structure. Our conversion electron Mössbauer spectroscopy studies of this system verified the existence of the tetragonal phase, which is responsible for the perpendicular anisotropy. The ordering process is influenced by the complicated growth of Fe on Au, as shown by the atomic scale scanning tunneling microscopy investigations. Other systems to be presented are FeAl (strong ordering mechanism in the bulk) and FeCr (miscible in the wide concentration range) monoatomi

Magnetic Properties of Fe3O4Fe_3O_4 Films on Fe(001)

We investigated the magnetic properties of ultrathin magnetite films deposited directly on MgO(001) and on a Fe(001) buffer layer. In both cases the magnetite surface structure could be identified using low energy electron diffraction. The conversion electron MÖssbauer spectroscopy measurements proved that, for magnetite films deposited on the Fe buffer, superparamagnetic relaxation was strongly suppressed. The effect of a Fe overlayer on the magnetite film grown directly on MgO is considerably weaker. Longitudinal Kerr magnetometry indicated the presence of the ferromagnetic interfacial coupling between Fe and magnetite films. We conclude that the density of antiphase boundaries for films grown on the Fe buffer is lower than that of $Fe_3O_4$/MgO films

Photoemission electronic states of epitaxially grown magnetite films

Abstract The valence band photoemission spectra of epitaxially grown 300Á single crystalline magnetite films were measured by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K. The samples were grown either on MgO(0 0 1) (B termination) or on (0 0 1) Fe (iron-rich A termination), thus intentionally presenting different surface stoichiometry, i.e. also different surface electronic states. Four main features of the electron photoemission at about −1.0, −3.0, −5.5 and −10.0 eV below a chemical potential show systematic differences for two terminations; this difference depends on the electron outgoing angle. Our studies confirm sensitivity of angle resolved PES technique on subtleties of surface states

Observation of the domain structure in Fe-Au superlattices with perpendicular anisotropy ARTICLE IN PRESS

Abstract Polar Kerr Microscopy was used to visualize characteristic transitions and external magnetic field driven domain structure evolution in a perpendicularly magnetized Fe-Au AF/FM double multilayer structure. Real time imaging performed in the external magnetic field allowed for identification of all sublayers magnetization reversal in accordance with measured PMOKE magnetization curve, showing strong dependence of transition character on the interlayer coupling type and adjacent sublayers magnetization orientation. Exchange bias is an effect caused by interfacial exchange interaction between an antiferromagnet (AF) and a ferromagnet (F). While it has been observed in a variety of AF/F thin films systems, in most cases the ferromagnetic layers are spontaneously in-plane magnetized. There are only a few experiments know