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Full-Text Articles in Physics

Magnetism Of Fe Clusters Formed By Buffer-Layer Assisted Growth On Pt(997), J. Zhang, D. Repetto, V. Sessi, Jan Honolka, Axel Enders, Klaus Kern Aug 2013

Magnetism Of Fe Clusters Formed By Buffer-Layer Assisted Growth On Pt(997), J. Zhang, D. Repetto, V. Sessi, Jan Honolka, Axel Enders, Klaus Kern

Axel Enders

The growth and magnetism of nanometer size Fe clusters on stepped Pt surfaces is investigated by scanning tunneling microscopy (STM) and magneto-optical Kerr effect measurements (MOKE). The clusters are formed on xenon buffer layers of varying thickness and then brought into contact with the substrate by thermal desorption of the Xe. The cluster size is controlled by the thickness of the Xe layer. It is found that clusters of diameter smaller than the Pt terrace width of 2 nm are aligned along the step edges of the Pt(997), thus forming linear cluster chains. In this arrangement, the clusters are ...


Ordered Layers Of Co Clusters On Bn Template Layers, J. Zhang, V. Sessi, C. H. Michaelis, I. Brihuega, Jan Honolka, K. Kern, Ralph Skomski, X. Chen, Geoffrey Rojas, Axel Enders Aug 2013

Ordered Layers Of Co Clusters On Bn Template Layers, J. Zhang, V. Sessi, C. H. Michaelis, I. Brihuega, Jan Honolka, K. Kern, Ralph Skomski, X. Chen, Geoffrey Rojas, Axel Enders

Axel Enders

The synthesis of highly ordered monolayers of metallic nanoclusters by a buffer-layer assisted growth (BLAG) route is introduced and investigated. The focus is on clusters of Co deposited onto mechanically stable, periodically corrugated boron-nitride layers by repeated BLAG cycles. The approach combines the advantages of well-established preparation methods for surface-supported clusters; namely, the versatility of cluster deposition from the gas phase and the positional accuracy of the directed growth on template surfaces. The particle coverage and geometry are obtained from scanning tunneling microscopy experiments, and analyzed with analytic models and by Monte Carlo simulations. The model shows that the approach ...


Spin-Dependent Transport In Fe And Fe/Au Multilayers, Theodore L. Monchesky, Axel Enders, R. Urban, Kenneth Myrtle, Brett Heinrich, X.-G. Zhang, William H. Butler, J. Kirschner Aug 2013

Spin-Dependent Transport In Fe And Fe/Au Multilayers, Theodore L. Monchesky, Axel Enders, R. Urban, Kenneth Myrtle, Brett Heinrich, X.-G. Zhang, William H. Butler, J. Kirschner

Axel Enders

In situ resistance measurements of epitaxial Fe layers and Au/Fe bilayers were used to quantify the scattering in giant magnetoresistance (GMR) spin valve structures. The semiclassical Boltzmann transport equation, incorporating first-principles local density functional calculations, fitted the thickness dependence of the conductivity. Fits to the data indicate that Fe has a large spin asymmetry with bulk relaxation times τ↓=3.0 × 10−14 s and τ↑=2.5 × 10−15 s. These give a conductivity equal to that of bulk Fe. The interface scattering from the Fe/GaAs, the Fe/vacuum, and the Au/vacuum interfaces is purely diffuse ...


Magnetic Anisotropy In Itinerant Magnets, Ralph Skomski, Arti Kashyap, A. Solanki, Axel Enders, David J. Sellmyer Aug 2013

Magnetic Anisotropy In Itinerant Magnets, Ralph Skomski, Arti Kashyap, A. Solanki, Axel Enders, David J. Sellmyer

Axel Enders

The structural dependence of the magnetocrystalline anisotropy of itinerant permanent magnets (or nanostructures of iron-series 3d elements) is investigated by model and tight-binding calculations. Magnetic nanostructures yield strong oscillations of the anisotropy as a function of the number of d electrons per atom, which can be tuned by alloying. While interatomic hopping is usually more important in metals than crystal-field interactions, we find substantial crystal-field corrections for some configurations, especially for the atomic square. Finally, we compare our results with Néel model.


Self-Assembly And Properties Of Nonmetalated Tetraphenyl-Porphyrin On Metal Substrates, Geoffrey Rojas, Xumin Chen, Cameron Bravo, Ji-Hyun Kim, Jae-Sung Kim, Jie Xiao, Peter A. Dowben, Yi Gao, Xiao Cheng Zeng, Wonyoung Choe, Axel Enders Aug 2013

Self-Assembly And Properties Of Nonmetalated Tetraphenyl-Porphyrin On Metal Substrates, Geoffrey Rojas, Xumin Chen, Cameron Bravo, Ji-Hyun Kim, Jae-Sung Kim, Jie Xiao, Peter A. Dowben, Yi Gao, Xiao Cheng Zeng, Wonyoung Choe, Axel Enders

Axel Enders

The structure−electronic structure relationship of nonmetalated meso-tetraphenyl porphyrin (2H-TPP) on the (111) surfaces of Ag, Cu, and Au was studied with a combination of scanning tunneling microscopy, photoelectron spectroscopy, and density functional theory. We observe that the molecules form a 2D network on Ag(111), driven by attractive intermolecular interactions, while the surface migration barriers are comparatively small and the charge transfer to the adsorbed molecules is minimal. This is in contrast to a significant charge transfer observed in 2H-TPP/Cu(111), resulting in repulsive forces between the molecules that prevent molecular adlayer network formation. It is shown that ...


Nanomagnetic Skyrmions, Ralph Skomski, Zhen Li, Rui Zhang, Roger Kirby, Axel Enders, Daniel Schmidt, T. Hofmann, Eva Schubert, David Sellmyer Aug 2013

Nanomagnetic Skyrmions, Ralph Skomski, Zhen Li, Rui Zhang, Roger Kirby, Axel Enders, Daniel Schmidt, T. Hofmann, Eva Schubert, David Sellmyer

Axel Enders

Magnetic skyrmions and other topologically protected nanostructures are investigated. Since skyrmions are mathematical rather than physical objects, they describe a wide variety of physical systems, from simple magnetic domain walls to complicated quantum phases with long-range many-body entanglement. Important distinctions concern the skyrmions’ relativistic character, their quantum-mechanical or classical nature, and the one- or many-body character of the wave functions. As specific examples we consider magnetic nanospirals, where the topology of a vortex-like spin state is protected by magnetostatic interactions, and edge currents in dilute magnetic semiconductors and metallic nanodots. Our analysis militates against giant orbital moments created by a ...


Temperature Dependence Of Metal-Organic Heteroepitaxy, Geoffrey Rojas, Xumin Chen, Donna Kunkel, Matthias Bode, Axel Enders Aug 2013

Temperature Dependence Of Metal-Organic Heteroepitaxy, Geoffrey Rojas, Xumin Chen, Donna Kunkel, Matthias Bode, Axel Enders

Axel Enders

The nucleation and growth of 2D layers of tetraphenyl porphyrin molecules on Ag(111) are studied with variable-temperature scanning tunneling microscopy. The organic/metal heteroepitaxy occurs by strict analogy to established principles for metal heteroepitaxy. A hierarchy of energy barriers for diffusion on terraces and along edges and around corners of adislands is established. The temperature is key to activating these barriers selectively, thus determining the shape of the organic aggregates, from a fractal shape at lower temperatures to a compact shape at higher temperatures. The energy barriers for the terrace diffusion of porpyrins and the molecule-molecule binding energy were ...


Magnetism Of Fe Clusters And Islands On Pt Surfaces, D. Repetto, Jan Honolka, S. Rusponi, H. Brune, Axel Enders, Klaus Kern Aug 2013

Magnetism Of Fe Clusters And Islands On Pt Surfaces, D. Repetto, Jan Honolka, S. Rusponi, H. Brune, Axel Enders, Klaus Kern

Axel Enders

Clusters and islands of Fe atoms have been prepared by noble gas buffer layer assisted growth as well as by standard molecular beam epitaxy on Pt substrates. Xe buffer layers have been utilized to promote the formation of compact, relaxed Fe clusters with narrow size distribution. Without the Xe buffer, strained Fe islands with a characteristic misfit dislocation network are formed. Magnetization loops obtained by magneto-optical Kerr effect measurements reveal that in-plane easy magnetization axis is only found for the relaxed clusters, pointing out the important role of epitaxial lattice deformations for the magnetic anisotropy.


Entropy Localization In Magnetic Compounds And Thin-Film Nanostructures, Ralph Skomski, Christian Binek, Steven A. Michalski, Tathagata Mukherjee, Axel Enders, David J. Sellmyer Aug 2013

Entropy Localization In Magnetic Compounds And Thin-Film Nanostructures, Ralph Skomski, Christian Binek, Steven A. Michalski, Tathagata Mukherjee, Axel Enders, David J. Sellmyer

Axel Enders

The effect of nanostructuring on the magnetic entropy of materials for room-temperature magnetic cooling is investigated by model calculations. The materials are structurally inhomogeneous with a large number of nonequivalent crystallographic sites. In the mean-field Heisenberg model, the entropy density is a unique function of the local magnetization so that the coupled set of nonlinear mean-field equations yields not only the magnetization but also the entropy density. Since most of the entropy is localized near grain boundaries, nanomagnetic cooling requires small feature sizes. Magnetic anisotropy is a substantial complication, even on a mean-field level, but the corresponding corrections are often ...


Substrate Dependent Buffer-Layer Assisted Growth Of Nanoclusters, Jan Honolka, Violetta Sessi, Jian Zhang, Simon Hertenberger, Axel Enders, Klaus Kern Aug 2013

Substrate Dependent Buffer-Layer Assisted Growth Of Nanoclusters, Jan Honolka, Violetta Sessi, Jian Zhang, Simon Hertenberger, Axel Enders, Klaus Kern

Axel Enders

The role of the substrate on the morphology of nanometer size clusters fabricated by buffer layer assisted growth (BLAG) was studied using scanning tunneling microscopy. Clusters of Fe and Co were deposited on Ag(111), Cu(100), Rh(111), and Pt(111) surfaces using identical BLAG parameters, which are temperature, as well as metal and buffer layer coverage. Semi-hemispherical clusters are found on Ag(111) and Cu(100), while flat monolayer high islands are observed on Rh(111) and Pt(111) due to complete wetting. The results of this study are in agreement with the common notion that BLAG is ...


Complex Domain-Wall Dynamics In Compressively Strained Ga1−XMnXAs Epilayers, Liza Herrera Diez, Reinhard K. Kremer, Axel Enders, Matthias Rössle, Erhan Arac, Jan Honolka, Klaus Kern, Ernesto Placidi, Fabrizio Arciprete Aug 2013

Complex Domain-Wall Dynamics In Compressively Strained Ga1−XMnXAs Epilayers, Liza Herrera Diez, Reinhard K. Kremer, Axel Enders, Matthias Rössle, Erhan Arac, Jan Honolka, Klaus Kern, Ernesto Placidi, Fabrizio Arciprete

Axel Enders

The domain-wall-induced reversal dynamics in compressively strained Ga1−xMnxAs was studied employing the magneto-optical Kerr effect and Kerr microscopy. Due to the influence of a uniaxial part in the in-plane magnetic anisotropy 90°± δ domain walls with considerably different dynamic behavior are observed. While the 90° + δ reversal is identified to be propagation dominated with a small number of domains, the case of 90°− δ reversal involves a larger number of nucleation centers. The domain-wall nucleation/propagation energies ε for both transitions are estimated using model calculations from which we conclude that single domain devices can be achievable using the ...


Stress And Structure Of Ni Monolayers On W(110): The Importance Of Lattice Mismatch, D. Sander, C. Schmidthals, Axel Enders, J. Kirschner Aug 2013

Stress And Structure Of Ni Monolayers On W(110): The Importance Of Lattice Mismatch, D. Sander, C. Schmidthals, Axel Enders, J. Kirschner

Axel Enders

The combination of in situ stress measurements, low-energy electron diffraction, and scanning tunneling microscopy reveals the intimate relation between film structure and film stress for epitaxial growth of Ni on W(110) in the monolayer range. In contradiction to lattice mismatch considerations, we measure tremendous compressive stress in the pseudomorphic Ni film, where tensile film stress is expected from strain arguments. Surface stress of the film-substrate composite is proposed to be much more relevant for the description of film stress in the submonolayer range than lattice mismatch arguments are.


Magic Alkali-Fullerene Compound Clusters Of Extreme Thermal Stability, Axel Enders, N. Malinowski, D. Ievlev, E. Zurek, Jochen Autschbach, Klaus Kern Aug 2013

Magic Alkali-Fullerene Compound Clusters Of Extreme Thermal Stability, Axel Enders, N. Malinowski, D. Ievlev, E. Zurek, Jochen Autschbach, Klaus Kern

Axel Enders

The thermal stability of free pure C60-, as well as C60-alkali, and -alkaline-earth metal compound clusters is investigated. We find that small (C60) m-clusters (m ≤ 6) decay at comparatively low temperatures below 400 K, as a consequence of weak intermolecular van der Waals interaction. Adding barium or potassium to the clusters dramatically increases the decay temperatures for “magic” configurations of (C60)mBa2m−1 and (C60)mK2m, which reach values as high as 1780 K. Contrary to common belief, the superstable compound clusters are not characterized by filled ...


Cobalt Nanoclusters On Metal-Supported Xe Monolayers: Influence Of The Substrate On Cluster Formation Kinetics And Magnetism, V. Sessi, K. Kuhnke, J. Zhang, J. Honolka, K. Kern, Axel Enders, P. Bencok, S. Bornemann, J. Minár, H. Ebert Aug 2013

Cobalt Nanoclusters On Metal-Supported Xe Monolayers: Influence Of The Substrate On Cluster Formation Kinetics And Magnetism, V. Sessi, K. Kuhnke, J. Zhang, J. Honolka, K. Kern, Axel Enders, P. Bencok, S. Bornemann, J. Minár, H. Ebert

Axel Enders

The growth dynamics of submonolayer coverages of cobalt during buffer layer assisted growth on Ag(111) and Pt(111) substrates is investigated by variable temperature scanning tunneling microscopy in the temperature range between 80 and 150 K. It is found that attractive cluster-substrate interactions can govern the cluster formation on the Xe buffer layer if the Xe layer is sufficiently thin. The interpretation of the microscopy results is supported by x-ray magnetic circular dichroism data which monitor the effect of cluster-substrate interactions on the formation of magnetic moments and magnetic anisotropy of Co nanocluster during the different stages of growth ...


Structure And Magnetism Of Atomically Thin Fe Layers On Flat And Vicinal Pt Surfaces, D. Repetto, T. Lee, S. Rusponi, J. Honolka, K. Kuhnke, V. Sessi, U. Starke, H. Brune, P. Gambardella, C. Carbone, Axel Enders, K. Kern Aug 2013

Structure And Magnetism Of Atomically Thin Fe Layers On Flat And Vicinal Pt Surfaces, D. Repetto, T. Lee, S. Rusponi, J. Honolka, K. Kuhnke, V. Sessi, U. Starke, H. Brune, P. Gambardella, C. Carbone, Axel Enders, K. Kern

Axel Enders

Ultrathin Fe films on Pt substrates have been investigated under ultrahigh vacuum conditions by scanning tunneling microscopy, low energy electron diffraction, magneto-optical Kerr effect, x-ray magnetic circular dichroism measurements, and Kerr microscopy. We present a comparison between Fe films on flat Pt(111) and stepped Pt(997), with particular focus on the magnetic anisotropy in the submonolayer thickness range below 0.2 monolayer coverage, and above the spin reorientation transition at 3 monolayer thickness. The comparison of structure and magnetism suggests that the perpendicular easy axis found for films thinner than three monolayers is due to dominating contributions from both ...


Ultrathin Batio3 Templates For Multiferroic Nanostructures, Xumen Chen, Seolun Yang, Ji-Hyun Kim, Hyung-Do Kim, Jae-Sung Kim, Geoffrey Rojas, Ralph Skomski, Haidong Lu, Anand Bhattacharya, Tiffany Santos, Nathan Guisinger, Matthias Bode, Alexei Gruverman, Axel Enders Aug 2013

Ultrathin Batio3 Templates For Multiferroic Nanostructures, Xumen Chen, Seolun Yang, Ji-Hyun Kim, Hyung-Do Kim, Jae-Sung Kim, Geoffrey Rojas, Ralph Skomski, Haidong Lu, Anand Bhattacharya, Tiffany Santos, Nathan Guisinger, Matthias Bode, Alexei Gruverman, Axel Enders

Axel Enders

The structural, electronic and dielectric properties of high-quality ultrathin BaTiO3 films were investigated. The films, which were grown by ozone-assisted molecular beam epitaxy on Nb-doped SrTiO3(001) substrates and have thicknesses as low as 8 unit cells (u.c.) (3.2 nm), are unreconstructed and atomically smooth with large crystalline terraces. A strain-driven transition to three-dimensional (3D) island formation is observed for films of 13 u.c. thickness (5.2 nm). The high structural quality of the surfaces, together with dielectric properties similar to bulk BaTiO3 and dominantly TiO2 surface termination, makes these films suitable templates for the synthesis of ...


Is The Magnetic Anisotropy Proportional To The Orbital Moment?, Ralph Skomski, Arti Kashyap, Axel Enders Aug 2013

Is The Magnetic Anisotropy Proportional To The Orbital Moment?, Ralph Skomski, Arti Kashyap, Axel Enders

Axel Enders

The relation between orbital moment and magnetic anisotropy is investigated by model calculations, which show that only a part of the spin-orbit coupling contributes to the anisotropy. A large part of the anisotropy energy, about 50% for iron series elements and nearly 100% for rare-earths, is stored in the nonrelativistic part of the Hamiltonian. A feature important for x-ray magnetic circular dichroism is that the orbital moment of heavy atoms rotates with the spin moment, whereas in light atoms, the orbital moment is recreated in each different direction. In the discussion, we consider three examples of current interest in different ...


Cobalt Nanoclusters On Metal-Supported Xe Monolayers: Influence Of The Substrate On Cluster Formation Kinetics And Magnetism, V. Sessi, K. Kuhnke, J. Zhang, Jan Honolka, Klaus Kern, Axel Enders, P. Bencok, S. Bornemann, J. Minár, Hubert Ebert Aug 2013

Cobalt Nanoclusters On Metal-Supported Xe Monolayers: Influence Of The Substrate On Cluster Formation Kinetics And Magnetism, V. Sessi, K. Kuhnke, J. Zhang, Jan Honolka, Klaus Kern, Axel Enders, P. Bencok, S. Bornemann, J. Minár, Hubert Ebert

Axel Enders

The growth dynamics of submonolayer coverages of cobalt during buffer-layer assisted growth on Ag(111) and Pt(111) substrates is investigated by variable temperature scanning tunneling microscopy in the temperature range between 80 and 150 K. It is found that attractive cluster-substrate interactions can govern the cluster formation on the Xe buffer layer if the Xe layer is sufficiently thin. The interpretation of the microscopy results is supported by x-ray magnetic circular dichroism data which monitor the effect of cluster-substrate interactions on the formation of magnetic moments and magnetic anisotropy of Co nanocluster during the different stages of growth. Ab ...


Length Scales Of Interactions In Magnetic, Dielectric, And Mechanical Nanocomposites, Ralph Skomski, Balamurugan Balamurugan, Eva Schubert, Axel Enders, David J. Sellmyer Aug 2013

Length Scales Of Interactions In Magnetic, Dielectric, And Mechanical Nanocomposites, Ralph Skomski, Balamurugan Balamurugan, Eva Schubert, Axel Enders, David J. Sellmyer

Axel Enders

It is investigated how figures of merits of nanocomposites are affected by structural and interaction length scales, Aside from macroscopic effects without characteristic lengths scales and atomic-scale quantum-mechanical interactions there are nanoscale interactions that reflect a competition between different energy contributions. We consider three systems, namely dielectric media, carbon-black reinforced rubbers and magnetic composites. In all cases, it is relatively easy to determine effective materials constants, which do not involve specific length scales. Nucleation and breakdown phenomena tend to occur on a nanoscale and yield a logarithmic dependence of figures of merit on the macroscopic system size. Essential system-specific differences ...


Surface State Engineering Of Molecule–Molecule Interactions, Geoffrey Rojas, Scott Simpson, Xumin Chen, Donna A. Kunkel, Justin Nitz, Jie Xiao, Peter A. Dowben, Eva Zurek, Axel Enders Aug 2013

Surface State Engineering Of Molecule–Molecule Interactions, Geoffrey Rojas, Scott Simpson, Xumin Chen, Donna A. Kunkel, Justin Nitz, Jie Xiao, Peter A. Dowben, Eva Zurek, Axel Enders

Axel Enders

Engineering the electronic structure of organics through interface manipulation, particularly the interface dipole and the barriers to charge carrier injection, is of essential importance to improve organic devices. This requires the meticulous fabrication of desired organic structures by precisely controlling the interactions between molecules. The well-known principles of organic coordination chemistry cannot be applied without proper consideration of extra molecular hybridization, charge transfer and dipole formation at the interfaces. Here we identify the interplay between energy level alignment, charge transfer, surface dipole and charge pillow effect and show how these effects collectively determine the net force between adsorbed porphyrin 2H-TPP ...


Magnetism Of Fept Surface Alloys, Jan Honolka, T. Y. Lee, K. Kuhnke, Axel Enders, Ralph Skomski, S. Bornemann, S. Mankovsky, J. Minar, J. Staunton, H. Ebert, M. Hessler, K. Fauth, G. Schutz, A. Buchsbaum, M. Schmid, P. Varga, K. Kern Aug 2013

Magnetism Of Fept Surface Alloys, Jan Honolka, T. Y. Lee, K. Kuhnke, Axel Enders, Ralph Skomski, S. Bornemann, S. Mankovsky, J. Minar, J. Staunton, H. Ebert, M. Hessler, K. Fauth, G. Schutz, A. Buchsbaum, M. Schmid, P. Varga, K. Kern

Axel Enders

The complex correlation of structure and magnetism in highly coercive monoatomic FePt surface alloys is studied using scanning tunneling microscopy, x-ray magnetic circular dichroism, and ab initio theory. Depending on the specific lateral atomic coordination of Fe either hard magnetic properties comparable to that of bulk FePt or complex noncollinear magnetism due to Dzyaloshinski-Moriya interactions are observed. Our calculations confirm the subtle dependence of the magnetic anisotropy and spin alignment on the local coordination and suggest that 3D stacking of Fe and Pt layers in bulk L10 magnets is not essential to achieve high-anisotropy values.


A Simple Technique To Measure Stress In Ultrathin Films During Growth, D. Sander, Axel Enders, J. Kirschner Aug 2013

A Simple Technique To Measure Stress In Ultrathin Films During Growth, D. Sander, Axel Enders, J. Kirschner

Axel Enders

We demonstrate an easy implementation of the cantilever bending beam approach to measure stress during film growth in ultrahigh vacuum. Using a simple and compact optical deflection technique, film stress with sub-monolayer sensitivity can be detected. A stress measurement during FeSi, formation on Si(l11) is presented.


Structure And Perpendicular Magnetization Of Fe/Ni(111) Bilayers On W(110), D. Sander, Axel Enders, C. Schmidthals, J. Kirschner, H. L. Johnston, C. S. Arnold, David E. Venus Aug 2013

Structure And Perpendicular Magnetization Of Fe/Ni(111) Bilayers On W(110), D. Sander, Axel Enders, C. Schmidthals, J. Kirschner, H. L. Johnston, C. S. Arnold, David E. Venus

Axel Enders

Scanning tunneling microscopy and low energy electron diffraction show that high quality fcc Ni(111) films can be prepared on W(110). The subsequent coverage of this Ni template by monolayers of Fe leads to a Fe/Ni bilayer with striking magnetic properties. The Fe cap layer induces a spin reorientation of the easy axis of magnetization from in-plane to perpendicular to the film, as checked with the magneto-optic Kerr effect. At higher Fe coverages, an in-plane magnetization of the bilayer is found, which is proposed to be caused by the fcc to bcc transition in the Fe layer.


A Combined Heating Cooling Stage For Cluster Thermalization In The Gas Phase, D. N. Ievlev, A. Küster, Axel Enders, N. Malinowski, H. Schaber, Klaus Kern Aug 2013

A Combined Heating Cooling Stage For Cluster Thermalization In The Gas Phase, D. N. Ievlev, A. Küster, Axel Enders, N. Malinowski, H. Schaber, Klaus Kern

Axel Enders

We report on the design and performance of a combined heating/cooling stage for the thermalization of clusters in a gas phase time-of-flight mass spectrometer. With this setup the cluster temperature can sensitively be adjusted within the range from 100 up to 800 K and higher. The unique combination of a heating stage with a subsequent cooling stage allows us to perform thermodynamic investigations on clusters at very high temperatures without quality losses in the spectra due to delayed fragmentation in the drift tube of the mass spectrometer. The performance of the setup is demonstrated by the example of (C60 ...


Anisotropy Of Zigzag Chains Of Palladium, P. K. Sahota, Ralph A. Skomski, Axel Enders, David J. Sellmyer, Arti Kashyap Aug 2013

Anisotropy Of Zigzag Chains Of Palladium, P. K. Sahota, Ralph A. Skomski, Axel Enders, David J. Sellmyer, Arti Kashyap

Axel Enders

Ab initio calculations of the biaxial anisotropy of infinite Pd zigzag chains are presented. The simulations were performed with the Vienna Ab-Initio Simulation Package, using a tetragonal unit cell with a supercell approach where the atoms are repeated along the z-direction. The anisotropy is determined from the energies along the three principal directions [001], [100], and [010]. The second-order anisotropy constants K1 and K'1 were extracted by fitting the calculated energy values to the phenomenological energy. The easiest magnetization direction is along the wire axis, whereas the hardest direction is perpendicular to the plane of the wire. The calculated ...


Magnetic Anisotropy Of Deposited Transition Metal Clusters, S. Bornemann, J. Minar, J.B. Staunton, Jan Honolka, Axel Enders, Hubert Ebert Aug 2013

Magnetic Anisotropy Of Deposited Transition Metal Clusters, S. Bornemann, J. Minar, J.B. Staunton, Jan Honolka, Axel Enders, Hubert Ebert

Axel Enders

We present results of magnetic torque calculations using the fully relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one can derive amongst others the magnetic anisotropy energy (MAE). It was found that this approach is numerically much more stable and also computationally less demanding than using the magnetic force theorem that allows to calculate the MAE directly. Although structural relaxation effects were not included our results correspond reasonably well to recent experimental data.


Strain Dependence Of The Magnetic Properties Of Nm Fe Films On W(100), Axel Enders, D. Sander, J. Kirschner Aug 2013

Strain Dependence Of The Magnetic Properties Of Nm Fe Films On W(100), Axel Enders, D. Sander, J. Kirschner

Axel Enders

The thickness dependence of the magneto-elastic coupling B1, the intrinsic film stress, and the magnetic in-plane anisotropy K4 of Fe films on W(100) are measured with an in situ combination of a highly sensitive optical deflection technique with magneto-optical Kerr-effect measurements. We find that both B1 and K4 depend strongly on the Fe film thickness. The thickness dependence of B1 can be described by considering a second order magneto-elastic coupling constant D = GJ/m3 as a strain dependent correction of B1. We tentatively ascribe the deviation of K4 from its bulk value to the tetragonal lattice distortion caused by ...


Structural Transition In (C60)N Clusters, W. Branz, N. Malinowski, Axel Enders, T. P. Martin Aug 2013

Structural Transition In (C60)N Clusters, W. Branz, N. Malinowski, Axel Enders, T. P. Martin

Axel Enders

The structure of (C60) n clusters (n = 1– 150) was investigated by heating them to definite temperatures in a helium bath (heating cell) with subsequent characterization in a time-of-flight mass spectrometer. The intensity anomalies in the resulting mass spectra reflect particularly stable configurations that resisted evaporation. However, the set of enhanced peaks (magic numbers) turned out to be temperature dependent. Clusters heated to a moderate temperature of 490 K yielded mass spectra indicating the presence of icosahedral structures that can be characterized by a set of unusually strong peaks, namely n = 13, 19, 23, 26, 35, 39, 43, 46 ...


Combined Kerr Microscope And Magnetic Force Microscope For Variable Temperature Ultrahigh Vacuum Investigations, D. Peterka, Axel Enders, G. Haas, Klaus Kern Aug 2013

Combined Kerr Microscope And Magnetic Force Microscope For Variable Temperature Ultrahigh Vacuum Investigations, D. Peterka, Axel Enders, G. Haas, Klaus Kern

Axel Enders

A new system combining a Kerr microscope and a magnetic force microscope for the study of magnetic domains in ultrathin films under ultrahigh vacuum conditions is presented. Due to the overlapping imaging range of both techniques magnetic domains can be investigated over a lateral range from millimeter down to fractions of a micrometer. Experiments can be done at variable temperatures, from 80 K to 600 K. First results are presented showing the same magnetic domain in a three monolayer Fe film on Cu (100) imaged with both techniques.


Magnetic Susceptibility Of Nanoscale Kondo Systems, Ralph Skomski, R. Zhang, Parashu Kharel, Axel Enders, Sy_Hwang Liou, D. J. Sellmeyer Aug 2013

Magnetic Susceptibility Of Nanoscale Kondo Systems, Ralph Skomski, R. Zhang, Parashu Kharel, Axel Enders, Sy_Hwang Liou, D. J. Sellmeyer

Axel Enders

The mesoscopic Kondo effect in metallic nanoparticles containing a magnetic impurity is investigated by model calculations. A Maxwell–Garnett approach is used to approximately determine the resistivity of doped nanoparticles in a matrix, and the magnetic susceptibility is estimated from the confinement of the conduction electrons. Conductivity measurements of nanoparticles embedded in a matrix are difficult to realize, because metallic matrices distort the Kondo cloud, whereas insulating or semiconducting matrices yield a very weak signal. By comparison, susceptibility measurements do not suffer from these shortcomings. The Kondo effect survives in nanoparticles even if the cluster size is much smaller than ...