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The known Brüche-Recknagel formula for determining the resolving power of an emission electron microscope (EEM) was derived assuming idealized conditions: the object surface was planar, and the accelerating electric field was homogeneous. However, deviations from these conditions will deteriorate the resolving power. This can be caused by a surface topography as well as local electric or magnetic fields on the object surface. In the present paper the resolving power of an EEM is calculated for the case when there are local magnetic fields on the object surface. The deterioration of the resolving power will then depend on the local field strength not only in the given point of the object surface, but also in adjacent regions. The estimations performed show that the lateral resolution in EEM under the influence of magnetic microfields of real ferromagnets can be several times worse than in the case of the absence of these fields.

Spin valve systems are widely considered in magnetic rotation angle sensors. We present a simple magnetostatic model to simulate the electrical and magnetic signal of typical spin valve systems as a function of external magnetic field and rotation angle. To match simulation and experiment only a few parameters are needed, which can be determined by a single measurement. Two types of systems are treated and discussed: a simple spin valve and a spin valve with an “artificial antiferromagnet,” often used to enhance the exchange bias. The model shows a very good correspondence of the predictions to the experimental results of the systems investigated. In order to quantitatively compare experiment and model, we introduce a useful concept to quantify the quality of the angle rotation curves: the total harmonic distortion.

Structural, transport and magnetic properties of sputtered Ni80Fe20/Cu multilayers showing giant magnetoresistance (GMR) were studied using X-ray reflectometry and diffraction, transport measurements, ferromagnetic resonance (FMR), and magneto-optical Kerr effect. In particular, mechanisms of the GMR degradation at elevated temperatures were investigated. Multilayers with an individual layer thickness of 2 nm show a sharp drop of the GMR after annealing at about 250°C. Whereas below this temperature grain growth and defect reduction contribute to a partial improvement of the GMR, above ∼250°C interdiffusion between Ni and Cu appears to lead to layer intermixing and to the degradation of transport and magnetic properties. Moreover, the initial 〈1 1 1〉 texture sharpens, and strong tensile stresses arise in the layer stack. We correlated the structural alterations to changes in the magnetic properties such as the strength of the antiferromagnetic coupling (bilinear and biquadratic) and the magnetic anisotropy. Above 250°C an increasing magnetic inhomogeneity of the Permalloy layers can be inferred from the FMR linewidth broadening.

The evolution of the layer and crystallite structure of nanoscale Co/Cu multilayers was studied during annealing up to 740 °C. Two structural transformations were observed. Between 310 and 410 °C the initial 〈111〉 fibre texture altered into a 〈100〉 texture, accompanied by the growth of 〈100〉 crystallites. During annealing, the presence of strong coherency strains in the multilayer stacking was inferred from satellite reflection analysis. These strains are considered as a driving force for the texture change due to the elastic anisotropy of copper and fcc-cobalt. As a second transformation the decay of the multilayer stacking sets in above 470 °C and leads to the formation of a granular structure which predominates above 650 °C. Both structural alterations were observed during heating, whereas during cooling no further transformations occurred.

It is shown that magnetic X-ray circular dichroism (MXCD) can be exploited in photoemission electron microscopy not only to visualize the domain structure of ferromagnets, but also to perform quantitative measurements of the stray magnetic fields at the domain boundaries. In the general situation, two MXCD images obtained at different extractor voltages are required. In specific cases, however, it suffices to consider a single image, if it is deformed by the stray magnetic fields compared to a known object geometry. The object geometry means its real shape, scratches or other defects. It is also possible to deposit a paramagnetic film structured in the form of stripes or a grid as a reference on the ferromagnetic sample being investigated.

Perpendicularly magnetized ferrimagnetic Gd–Fe–Co thin films with different compositions and multilayer arrangements were subjected to femtosecond laser pulses. The pulses triggered different magnetization dynamics in the various thin films. In the Gd26Fe66Co8 film, which has an angular-momentum-compensation temperature (T A) well above ambient temperature (T exp), monotonic magnetization reversal occurred, whereas the Gd22Fe70Co8 film (where T A is well below T exp) exhibited remarkable wavelike spin modulation with spatial inhomogeneity during relaxation of the laser-induced nonequilibrium state. These findings can enable broad-range tuning of the magneto-optical responses of Gd–Fe–Co alloys, facilitating advances in materials engineering.

We present an electronic structure study of a magnetic oxide/ semiconductor model system, EuO on silicon, which is dedicated for efficient spin injection and spin detection in silicon-based spintronics devices. A combined electronic structure analysis of Eu core levels and valence bands using hard X-ray photoemission spectroscopy was performed to quantify the nearly ideal stoichiometry of EuO “spin filter” tunnel barriers directly on silicon, and the absence of silicon oxide at the EuO/Si interface. These results provide evidence for the successful integration of a magnetic oxide tunnel barrier with silicon, paving the way for the future integration of magnetic oxides into functional spintronics devices. Hard X-ray photoemission spectroscopy of an Al/EuO/Si heterostructure probing the buried EuO and EuO/Si interface. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The intensity of surface spin wave excitations in inelastic electron scattering is measured as function of electron energy for fcc and hexagonal close packed (hcp) cobalt layers. Intensities are converted into scattering probabilities with the help of a recently established calibration of our spectrometer. The scattering probability as function of energy exhibits a peak around 7 and 3 eV for fcc and hcp cobalt, respectively, and decays to immeasurably small values at energies above 10 to 15 eV in stark contrast to theoretical predictions. By comparison to phonon scattering the peaks in the scattering probabilities at low energies are tentatively attributed to image potential induced resonances.

Electron magnetic circular dichroism (EMCD) allows the quantitative, element-selective determination of spin and orbital magnetic moments, similar to its well-established X-ray counterpart, X-ray magnetic circular dichroism (XMCD). As an advantage over XMCD, EMCD measurements are made using transmission electron microscopes, which are routinely operated at sub-nanometre resolution, thereby potentially allowing nanometre magnetic characterization. However, because of the low intensity of the EMCD signal, it has not yet been possible to obtain quantitative information from EMCD signals at the nanoscale. Here we demonstrate a new approach to EMCD measurements that considerably enhances the outreach of the technique. The statistical analysis introduced here yields robust quantitative EMCD signals. Moreover, we demonstrate that quantitative magnetic information can be routinely obtained using electron beams of only a few nanometres in diameter without imposing any restriction regarding the crystalline order of the specimen.

By using laser-based high harmonic EUV sources, we make several advances in uncovering new understanding of correlated charge and spin dynamics on few femtosecond timescales, and in developing new element-specific capabilities for probing magnetic materials.

We present a procedure to prepare single-crystalline, high-purity Cu(001) films (templates) suitable as substrates for subsequent epitaxial thin-film growth. The template films were grown in a dedicated molecular-beam epitaxy system on a Cr/Ag/Fe/GaAs(001) buffer layer system. Low-energy electron diffraction and X-ray diffraction were applied to determine the surface orientation and the epitaxial relationship between all layers of the stack. Post-annealing at moderate temperatures enhances the quality of the film as shown by low-energy electron diffraction and atomic force microscopy. X-ray photoemission and Auger electron spectroscopy confirm that no atoms of the buffer layers diffuse into the Cu film during the initial preparation and the post-annealing treatment. The completed Cu(001) template system can be exposed to air and afterwards refurbished by Ar + -ion bombardment and annealing, enabling the transfer between vacuum systems. The procedure provides suitable conductive thin film templates for studies of epitaxial thin films, e.g. on the magnetic and magnetotransport properties of Co and Ni based films and multilayers.

We present a comprehensive study of the adsorption behavior of iron phthalocyanine on the low-index crystal faces of silver. By combining measurements of the reciprocal space by means of photoelectron momentum mapping and low energy electron diffraction, the real space adsorption geometries are reconstructed. At monolayer coverage ordered superstructures exist on all studied surfaces containing one molecule in the unit cell in case of Ag(100) and Ag(111), and two molecules per unit cell for Ag(110). The azimuthal tilt angle of the molecules against the high symmetry directions of the substrate is derived from the photoelectron momentum maps. A comparative analysis of the momentum patterns on the substrates with different symmetry indicates that both constituents of the twofold degenerate FePc lowest unoccupied molecular orbital are occupied by charge transfer from the substrate at the interface.

International audience; High-resolution X-ray photoemission electron microscopy (X-PEEM) is a well-established method for imaging ferroelectric domain structures. Here, we expand the scope of application of X-PEEM and demonstrate its capability for imaging and investigating domain walls in ferroelectrics with high-spatial resolution. Using ErMnO3 as test system, we show that ferroelectric domain walls can be visualized based on photo-induced charging effects and local variations in their electronic conductance can be mapped by analyzing the energy distribution of photoelectrons. Our results open the door for non-destructive, contract-free, and element-specific studies of the electronic and chemical structure at domain walls in ferroelectrics.

We introduce a method to test theoretical models for the layer dependence of exchange coupling constants in ultrathin magnetic films. The method is based on the observation of high-energy and high-momentum standing spin wave modes using high-resolution electron energy loss spectroscopy. Experimental data are presented for 5--8 layers of fcc cobalt deposited on Cu(100). The power of the method is illustrated by comparison to two theoretical studies predicting rather different results concerning the ratio of the interlayer and intralayer exchange coupling constants near the surface. Only the theory with a large interlayer coupling shows sufficient energy spreading in the layer dependence of the dispersion curves to match the experimental data. We furthermore discuss the reason for the surprising success of the simple nearest-neighbor Heisenberg model with a single exchange constant matched to experiment.

X-ray magnetic linear dichroism spectra measured in reflection (XMLD-R) on crystalline bcc Fe thin films across the 3 p absorption edges are reported. A series of measurements with varying orientation of the electric field vector of the linear polarized synchrotron radiation with respect to the crystal axes reveals a strong magnetocrystalline anisotropy in the XMLD-R spectra. The spectra agree well with theoretical spectra calculated within the framework of the density-functional theory accounting for the spin-orbital and exchange splitting of the 3 p semicore states on an equal footing.

The nanoscale electro-reduction in a memristive oxide is a highly relevant field for future non-volatile memory materials. Photoemission electron microscopy is used to identify the conducting filaments and correlate them to structural features of the top electrode that indicate a critical role of the three phase boundary (electrode-oxide-ambient) for the electro-chemical reduction. Based on simulated temperature profiles, the essential role of Joule heating through localized currents for electro-reduction and morphology changes is demonstrated. The three-phase boundary between electrode, oxide and ambient is shown to play a crucial role for the electroreduction in resistively switchable devices fabricated from Fe-doped SrTiO3. Nanoscale chemical mapping by X-ray photoemission electron microscopy, combined with simulated temperature profiles of the filaments, provide evidence that localized Joule heating at the electrode edge is essential for the formation of conducting filaments. \copyright 2014 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim.

The electronic structure and band alignment at metal/oxide interfaces for nonvolatile memory applications are investigated by hard x-ray photoelectron spectroscopy (HAXPES) and DC transport measurements, using acceptor doped SrTiO3 as a model memristive oxide. Metal-insulator-metal (MIM) structures with a noble metal (Pt) top electrode form a Schottky barrier and exhibit rectifying properties, while a reactive metal (Ti) as top electrode shows symmetric I(V) characteristics and a flat band situation at the interface. The transition from rectifying to ohmic I(V) relations with increasing Ti thickness is discussed with respect to the electrochemical reaction at the interface, the band alignment at the electrode/oxide interface, and the slope of the energy bands across the MIM structure.

In thin films of mixed ionic electronic conductors sandwiched by two ion-blocking electrodes, the homogeneous migration of ions and their polarization will modify the electronic carrier distribution across the conductor, thereby enabling homogeneous resistive switching. Here we report non-filamentary memristive switching based on the bulk oxide ion conductivity of amorphous GaOx (x~1.1) thin films. We directly observe reversible enrichment and depletion of oxygen ions at the blocking electrodes responding to the bias polarity by using photoemission and transmission electron microscopies, thus proving that oxygen ion mobility at room temperature causes memristive behaviour. The shape of the hysteresis I-V curves is tunable by the bias history, ranging from narrow counter figure-eight loops to wide hysteresis, triangle loops as found in the mathematically derived memristor model. This dynamical behaviour can be attributed to the coupled ion drift and diffusion motion and the oxygen concentration profile acting as a state function of the memristor.

The oxidation of sputtered NiFe(20 wt.%, Permalloy) thin films with a thickness of 180 nm was studied during annealing up to 400 °C for 2 h in air. The composition and the thickness of the oxide layer and the compositional change in the NiFe alloy layer as well as the microstructure of the film were investigated by Auger electron spectroscopy, X-ray diffraction, and transmission electron microscopy. Distinct oxidation starts at about 300 °C. The formed oxide layer consists of Fe 2 O 3 . The Fe concentration in the NiFe layer decreases with the oxidation which leads to changes of the properties of this layer.

The magnetic microstructure and magnetic coupling phenomena in thin-film systems, relevant for applications in magneto-electronics, are investigated by means of photoemission electron microscopy. Element-selective magnetic information is obtained by exploiting magnetic circular dichroism in the soft X-ray regime. The domain shape and sizes found at the surface of antiferromagnetically coupled metallic multilayers indicate the presence of a ferromagnetic coupling contribution, presumably caused by a build-up of roughness during the growth process. The magnetic domain patterns in FeNi microstructures on sputtered NiO films reflect the presence of a local exchange anisotropy, causing the phenomenon of exchange biasing or pinning of the ferromagnetic layer.

We have studied the effect of the dipolar magnetic coupling (also known as Neel coupling or “orange-peel” coupling) in tunneling magnetoresistive (TMR) elements. With an in situ scanning tunneling microscope we directly accessed the roughness of the films and found a close correspondence between the values for the coupling fields determined by the magneto-optical Kerr effect and the ones computed on the basis of the measured morphology parameters. We confirm an increase of the dipole coupling between the magnetic layers with decreasing barrier thickness as predicted by the model. Deviations from the theoretical predictions are observed for the case of thinner soft magnetic layers, which can be explained by reduced magnetization in very thin films. We demonstrate the importance of dipolar coupling for understanding the magnetic behavior of TMR elements by comparing TMR curves for optimized and nonoptimized structures.

The stress evolution on NiFe (20 wt.%) thin films with thickness of 170 nm was studied during thermal cycles up to maximal 530°C. The results are correlated to microstructural analyses carried out on samples cycled to various maximum temperatures by means of transmission electron microscopy, X-ray diffraction, and Auger electron spectroscopy. In addition, resistance-vs.-temperature measurements yielded more information about the microstructural evolution. The atomic rearrangement in grain boundaries is held responsible for a first irreversible stress contribution appearing between 150 and 300°C. A second, more distinct irreversible tensile stress contribution of approximately 400 MPa occurs between 300 and 400°C. It is explained by abnormal grain growth which can be observed in the same temperature range.

The thickness and temperature dependence of the angular distribution of the magnetic dichroism in photoemission from Co 2p core levels of Co/Cu(001) ultra-thin films has been investigated, using unpolarized Mg Kα radiation. Photoelectron spectra were collected for emission angles in a range of ±9° around the surface normal in the [001] azimuth. All asymmetry spectra were found to exhibit an identical spectral shape within the experimental error bar, but different scaling. The angular distribution of the Co 2p dichroic signal shows that at emission directions off the sample normal strong variations are present, in contrast to predictions from simple atomic theory. These crystallinity-related modulations were studied for Co films of different thicknesses [5, 3, 2, and 1.5 atomic monolayers (ML)] and different temperatures (100 and 300 K). They are higher for thicker films and lower temperatures. This experimental finding proves a diffraction picture, in which this modulation around the surface normal is explained by diffraction effects in forward scattering along the sample normal. As diffraction effects in magnetic dichroism combine both diffraction and magnetic dichroism, its behavior is influenced by both, structural and magnetic properties of the film.

Magnetic dichroism in photoemission has matured into a versatile and indispensable spectroscopic tool in surface and thin-film magnetism. Not only in core-level investigations, but also particularly in the analysis of valence electronic states (`band mapping'), magnetic dichroism reveals its merits. It allows one to characterize in detail the role of spin-orbit coupling in the valence bands, thereby arriving at a refined picture of the electronic structure of a ferromagnet. The various forms of magnetic dichroism, the underlying physical mechanisms, and selected results are discussed in a tutorial framework from an experimentalists point of view.

Structure, morphology, and magnetism of epitaxial Fe x Co 1~x alloy ultrathin "lms grown on Cu(1 0 0) in ultrahigh vacuum were investigated by a multi-technique approach over the whole composition range up to thicknesses of nine atomic monolayers (ML). Combining the results of the di!erent techniques it is found that the "lms grow at room temperature in a distorted FCC structure with random chemical order. The amount and sign of the distortion depend on thickness and composition. Below +60 to 70% Fe content the alloy "lms are smooth, and exhibit two di!erent vertical interlayer distances. At higher Fe concentrations several superstructures are observed, which are attributed to regular structural rearrangements. The structural relaxation above 4 ML thickness known from pure Fe "lms is not observed in the FeCo alloy "lms. Instead a gradual structural change towards a BCC(1 1 0) structure with increasing thickness occurs at higher Fe concentrations, and is still not complete in "lms as thick as 9 ML. The interrelation between morphology and structure in Fe x Co 1~x /Cu(1 0 0) is discussed in terms of composition-dependent lattice parameters and strain. An expansion of the "lms in the plane leads to a stabilization of the FCC structure, whereas a compression leads to corrugated "lms with a tendency towards structural transformations. The absence of the relaxed FCC structure found in pure Fe "lms is explained by Co atoms acting as defects in the FCC structure of the alloy "lms either in a geometrical sense and/or because of their di!erent magnetic moment with respect to the Fe atoms in both ferromagnetic and antiferromagnetic con"gurations of FCC Fe. ( 2000 Elsevier Science B.V. All rights reserved.

We report on a polarized neutron reflectivity investigation of the magnetization in Ge-based dilute magnetic semiconductors. We could observe a net magnetization from the splitting of the non-spin flip reflectivity patterns, which measure the magnetic moment parallel and antiparallel to the applied field. This contrast is visible at 50 K, at remanence and it is pronounced at higher fields even at 250 K for an inhomogeneous specimen. For a homogeneous sample the magnetic variation is visible only at 50 K and above 1.0 kOe. Thus, polarized neutron reflectivity can be a useful tool for investigating the magnetism in homogeneous and inhomogeneous thin film magnetic semiconductors.

The magnetization reversal behavior of 20 nm thick cobalt microstructures with a nanoconstriction of variable size has been studied using magnetoresistance measurements and micromagnetic simulations. Depending on the direction of the applied field relative to the current, reversible and irreversible switching events are observed, which can be explained using micromagnetic simulations. Anisotropic magnetoresistance (AMR) is the dominant resistance contribution in the systems measured. The simulations show that instead of one sharp domain wall, which may lead to ballistic magnetoresistance (BMR), two domain walls on each side of the nanocontact precede the complete reversal

The growth mode, morphology, and crystalline structure of Fe films on Cu 3 Au(100) are studied for diVerent growth temperatures (300 and 160 K ), using in situ scanning tunneling microscopy and low energy electron diVraction. Multilayer growth is found to be predominant for both growth temperatures. Only in films of 3‐4 monolayers (ML) grown at 300 K is a mixed mode of layer-bylayer growth and island growth observed. An fcc-to-bcc structural transformation, accompanied by a distinct change in the surface topography, starts at about 3.5 ML and 5.5 ML for the growth temperatures of 300 and 160 K, respectively. For both growth temperatures bcc-like Fe in Fe/Cu 3 Au(100) assumes, most likely through a Bain path, a surface plane with the (100) rather than the (110) orientation found in the Fe/Cu(100) system. Both the surface morphology and the onset thickness of the fcc‐bcc structural transformation are shown to be strongly aVected by the growth temperature. © 1998 Elsevier Science B.V. All rights reserved.

Ideal artificial materials such as magnetic thin films and superlattices are expected to possess unique properties owing to their reduced symmetry and dimensionality. In real systems, however, the actual behavior is extremely sensitive to the morphological features of the films and interfaces. {Co/Cu} heterostructures on Cu(111) are a prototypical example: their growth is complicated by several difficulties, such as the lack of interlayer diffusion or the appearance of stacking faults. We have been able to overcome these problems by using Pb as a surfactant during growth. In this way, ultrathin Co films and {Co/Cu} superlattices can be grown with custom-chosen properties: we can independently select to have either in-plane or out-of-plane magnetization, and ferro- or antiferro magnetic exchange coupling through the Cu spacer. The surfactant also prevents intermixing at the atomic steps, thus allowing us to grow one-dimensional structures (quantum wires).

Objective To study decay rates of productively and latently infected cells in peripheral blood and lymph nodes during triple antiretroviral therapy and the possible impact of interleukin-2 (IL-2) on viral kinetics. Methods: In this non-randomized study, nine antiretro-viral-naive HIV-positive patients received either saquinavir hard gel capsules 2400 mg three times daily (group I; four patients) or saquinavir soft gel capsules 1200 mg three times daily and IL-2 (group II), in both cases together with two nucleoside analogues. Plasma viraemia and lymphocyte subsets were analysed. Axillary lymph nodes were excised before and after 12 weeks of therapy. Lymph node sections were examined by in situ hybridization for HIV RNA, and productively infected cells were counted. Infection rates of FACS-sorted CD3, CD4 lymph node and peripheral blood mononuclear cells were determined by nested DNA PCR. Results Baseline plasma HIV RNA levels ranged from 1x106 copies/ml and remained undetectable throughout the study in one patient in group I. Plasma viraemia became undetectable after 3 months in four patients (three in group I). Productively infected cells were markedly reduced in the follow-up lymph node specimens. HIV DNA-positive CD4 T cells were reduced in lymphoid tissue and peripheral blood in all six evaluable patients. There were no significant differences between the groups in the clearance rates of plasma virus and of HIV DNA-positive cells. Conclusions Combined antiretroviral therapy rapidly suppressed active HIV replication in plasma and lymphoid tissue. Latently infected cells were cleared at a slower rate. Viral clearance did not appear to be markedly affected by additional IL-2 therapy.

The electronic structure of three monolayers (ML) Co on Cu(111), grown with Pb as a surfactant and capped with two ML Cu, was studied using magnetic circular dichroism in valence-band photoemission. The easy axis of magnetization in these films is perpendicular to the surface, allowing an experimental setup of extreme symmetry (photon spin, light incidence, electron emission, and magnetization all aligned and perpendicular to the surface). In such a geometry features observed in magnetic dichroism can be directly related to the symmetry character of the relativistic band structure. Experimental data in the photon energy range of 6--24 eV are presented. The observed magnetic dichroism and its dispersion with photon energy can be explained on the basis of direct transitions in a bulklike band structure of Co.

A spin-reorientation transition upon a variation of the Fe concentration $x$ is observed in ultrathin fcc ${\mathrm{Fe}}_{x}{\mathrm{Co}}_{1\ensuremath{-}x}$ alloy films on Cu(001) for $x$g77%. For film thicknesses below 4 monolayers the magnetic easy axis changes from in-plane on the Co-rich side to out-of-plane on the Fe-rich side. Since no structural transitions accompany this spin-reorientation transition, varying the alloy composition can be interpreted as varying the number of $3d$ electrons. Upon changing the average $d$-band filling by as little as 0.1 electron strong changes of the anisotropy energy are observed.

Interleaved low-energy electron diffraction (LEED) and magneto-optical Kerr effect (MOKE) measurements were carried out for room-temperature epitaxially grown FCC-like Fe/Cu(1 0 0) in the temperature range of 120–400 K. The structure of the Fe film was found to be not only dependent on thickness, as was believed previously, but also to be influenced by the temperature. Temperature-driven structural transitions were observed in the 4 and 4.5 ML films, this effect being more pronounced at 4 ML thickness. Whereas the whole 4 ML film assumes an FCC-like structure with a strong tetragonal expansion (FCT-like) at temperatures below 313 K, the bulk of the film relaxes into the ‘isotropic’ FCC-like structure and only the top layers remain expanded at temperatures above 333 K. Because only the FCT-like (expanded) Fe possesses ferromagnetic properties, the film becomes paramagnetic after heating above 333 K. This finding represents a new type of magnetic order-disorder transition and explains the lower value of the Curie temperature in the 4 ML Fe film as compared to 3 ML. In the 4.5 ML Fe film the similar correlation between the temperature-driven structural transition and an occurrence of the ferromagnetic long-range order was observed. Additionally, a pronounced difference in the energy positions of the characteristic maxima in the LEED I ( E ) curves for the (0 0) beam as well as a kinematic analysis of these curves imply a difference in the value of the tetragonal expansion for the entirely expanded FCC-like Fe film and the film expanded only in the topmost layers.

Co/Cu films were grown epitaxially on Cu(1 1 1), using Pb as a surfactant. The exchange coupling between Co layers separated by Cu is studied with magnetic circular dichroism in valence band photoemission. Direct evidence for complete antiferromagnetic coupling is observed at 4 monolayer Cu thickness for Co films both with perpendicular and in-plane remanent magnetization from the sign reversal of the dichroic asymmetry.

The magnetic properties, morphology, and crystallographic structure are studied for Fe films on Cu3Au~100! grown at room and low temperature, using in situ magneto-optical Kerr effect, scanning tunneling microscopy, and electron diffraction techniques. At T5160 K a spin-reorientation transition from perpendicular to in-plane magnetization occurs in films with Fe coverages starting from a critical thickness of 3.5 and 5.5 ML for room-temperature and low-temperature growth, respectively. Close to the critical thickness we observe an fcc-bcc structural transformation. The spin-reorientation transition is shown to be correlated to this structural change. This correlation may be explained by a drastic reduction of the perpendicular anisotropy induced by the fcc-bcc structural transformation. @S0163-1829~97!00809-6#

With the improved access to synchrotron radiation sources photoemission electron microscopy is developing into a versatile analytical tool in surface and materials science. The broad spectral range and the well-defined polarization characteristics of synchrotron light permit a unique combination of topographic, chemical, and even magnetic investigations down to a mesoscopic scale. The potentiality of photoemission electron microscopy is demonstrated by several experiments on surfaces and microstructured thin film systems, which have been carried out with a newly designed instrument. We discuss its different modes of operation with respect to both microscopy and spectroscopy. A combination of elemental selectivity and magnetic sensitivity is achieved by using circularly polarized soft X-rays and exploiting the effect of magnetic circular dichroism. This way one obtains information about the magnetic state of individual chemical components within the sample.

Magnetic dichroism of angle-resolved UV photoemission from fcc Co/Cu(001) thin films has been measured using linearly p-polarized light, and a coplanar geometry where the light and photoelectron wave vectors are antiparallel, and both are perpendicular to the in-plane sample magnetization. This geometry emphasizes information about state dispersion due to the crystalline symmetry. An orderly dispersion of the features in the magnetic dichroism over a wide range of off-normal angles of electron emission is related in detail to the bulk band structure of fcc Co. The measurements confirm the practical utility of magnetic dichroism experiments as a relatively simple complement to spin-resolved photoemission.

The electronic properties of fcc Fe Co/Cu(100) were investigated by spin-resolved photoelectron spectroscopy. At a fixed concentration a dispersion of the majority and minority bands with Δ 5 -symmetry towards higher binding energy along the Δ-axis of the Brillouin zone could be followed upon increasing photon energy. Upon variation of the concentration the spectra for the alloy films reveal a gradual shift of the Δ 5 minority spin band through the Fermi level and a change of the sign of the spin polarization at the Fermi level in full agreement with the expected tendency from Co to Fe. Such a behavior agrees with both a simple mixture of the Fe and Co electronic properties in a randomly mixed alloy film, and a chemical separation (clustering) of both constituents.

In the following, we show that the conclusions of our article titled “Ultrafast Demagnetization Measurements Using Extreme Ultraviolet Light: Comparison of Electronic and Magnetic Contributions” are correct. The Comment of Vodungbo et al. argues that a unique determination of the refractive index variation over time is not possible using the data set presented in our paper. Furthermore, it was suggested that the lack of uniqueness allows for the possibility of a very specific time-dependent trajectory of the refractive index in the complex plane that could give rise to a large nonmagnetic modulation of the measured asymmetry, in spite of a negligible change in the s-polarized reflectivity. In this Reply, we conclusively show that any nonmagnetic contribution to the measured asymmetry is indeed negligible (

Using electron energy loss spectroscopy, we have probed the spin waves of fcc(100) cobalt after capping with 1--3 atom layers of pseudomorphic nickel or up to 12 atom layers of copper. The intensity decay of the spin wave signal is quantitatively described by the mean-free path of the incident and the scattered electron within the capping layer. The observed spin waves are therefore localized at the cobalt side of the Co/Ni and Co/Cu interfaces. Compared to the free cobalt surface, the interface spin waves are downshifted in frequency. The effect is attributed to a reduced exchange interaction between cobalt atoms at the interface.

The study of ultrafast dynamics in magnetic materials provides rich opportunities for greater fundamental understanding of correlated phenomena in solid-state matter, because many of the basic microscopic mechanisms involved are as-yet unclear and are still being uncovered. Recently, two different possible mechanisms have been proposed to explain ultrafast laser induced magnetization dynamics: spin currents and spin-flip scattering. In this work, we use multilayers of Fe and Ni with different metals and insulators as the spacer material to conclusively show that spin currents can have a significant contribution to optically induced magnetization dynamics, in addition to spin-flip scattering processes. Moreover, we can control the competition between these two processes, and in some cases completely suppress interlayer spin currents as a sample undergoes rapid demagnetization. Finally, by reversing the order of the Fe/Ni layers, we experimentally show that spin currents are directional in our samples, predominantly flowing from the top to the bottom layer.

The magnitude of electron spin polarization in topologically protected surface states is an important parameter with respect to spintronics applications. In order to analyze the warped spin texture in Bi${}_{2}$Te${}_{3}$ thin films, we combine angle- and spin-resolved photoemission experiments with theoretical ab initio calculations. We find an in-plane spin polarization of up to $\ensuremath{\sim}$45$%$ in the topologically protected Dirac cone states near the Fermi level. The Fermi surface of the Dirac cone state is warped and shows an out-of-plane spin polarization of $\ensuremath{\sim}$15$%$. These findings are in quantitative agreement with dedicated simulations which find electron density of the Dirac cone delocalized over the first quintuple layer with spin reversal occurring in the surface atomic layer.