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Full-Text Articles in Physics

Self-Assembly Of Strongly Dipolar Molecules On Metal Surfaces, Donna A. Kunkel, James Hooper, Scott Simpson, Daniel P. Miller, Lucie Routaboul, Pierre Braunstein, Bernard Doudin, Sumit Beniwal, Peter A. Dowben, Ralph Skomski, Eva Zurek, Axel Enders Jan 2015

Self-Assembly Of Strongly Dipolar Molecules On Metal Surfaces, Donna A. Kunkel, James Hooper, Scott Simpson, Daniel P. Miller, Lucie Routaboul, Pierre Braunstein, Bernard Doudin, Sumit Beniwal, Peter A. Dowben, Ralph Skomski, Eva Zurek, Axel Enders

Axel Enders Publications

The role of dipole-dipole interactions in the self-assembly of dipolar organic molecules on surfaces is investigated. As a model system, strongly dipolar model molecules, p-benzoquinonemonoimine zwitterions (ZI) of type C6H2(· · · NHR)2(· · · O)2 on crystalline coinage metal surfaces were investigated with scanning tunneling microscopy and first principles calculations. Depending on the substrate, the molecules assemble into small clusters, nano gratings, and stripes, as well as in two-dimensional islands. The alignment of the molecular dipoles in those assemblies only rarely assumes the lowest electrostatic energy configuration. Based on calculations of the electrostatic energy for various experimentally observed molecular arrangements and ...


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 Jan 2012

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 Publications

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 ...


Temperature Dependence Of Metal-Organic Heteroepitaxy, Geoffrey Rojas, Xumin Chen, Donna A. Kunkel, Matthias Bode, Axel Enders Oct 2011

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

Axel Enders Publications

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 ...


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 2011

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 Publications

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 ...


Self-Assembled Nanometer-Scale Magnetic Networks On Surfaces: Fundamental Interactions And Functional Properties, Carlo Carbone, Sandra Gardonio, Paolo Moras, Samir Lounis, Marcus Heide, Gustav Bihlmayer, Nicolae Atodiresei, Peter Heinz Dederichs, Stefan Blügel, Sergio Vlaic, Anne Lehnert, Safia Ouazi, Stefano Rusponi, Harald Brune, Jan Honolka, Axel Enders, Klaus Kern, Sebastian Stepanow, Cornelius Krull, Timofey Balashov, Aitor Mugarza, Pietro Gambardella Apr 2011

Self-Assembled Nanometer-Scale Magnetic Networks On Surfaces: Fundamental Interactions And Functional Properties, Carlo Carbone, Sandra Gardonio, Paolo Moras, Samir Lounis, Marcus Heide, Gustav Bihlmayer, Nicolae Atodiresei, Peter Heinz Dederichs, Stefan Blügel, Sergio Vlaic, Anne Lehnert, Safia Ouazi, Stefano Rusponi, Harald Brune, Jan Honolka, Axel Enders, Klaus Kern, Sebastian Stepanow, Cornelius Krull, Timofey Balashov, Aitor Mugarza, Pietro Gambardella

Axel Enders Publications

Nanomagnets of controlled size, organized into regular patterns open new perspectives in the fields of nanoelectronics, spintronics, and quantum computation. Self-assembling processes on various types of substrates allow designing fine-structured architectures and tuning of their magnetic properties. Here, starting from a description of fundamental magnetic interactions at the nanoscale, we review recent experimental approaches to fabricate zero-, one-, and two-dimensional magnetic particle arrays with dimensions reduced to the atomic limit and unprecedented areal density. We describe systems composed of individual magnetic atoms, metal-organic networks, metal wires, and bimetallic particles, as well as strategies to control their magnetic moment, anisotropy, and ...


Is The Magnetic Anisotropy Proportional To The Orbital Moment?, Ralph Skomski, Arti Kashyap, Axel Enders Jan 2011

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

Axel Enders Publications

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 ...


Length Scales Of Interactions In Magnetic, Dielectric, And Mechanical Nanocomposites, Ralph Skomski, Balamurugan Balamurugan, Eva Schubert, Axel Enders, David J. Sellmyer Jan 2011

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

Axel Enders Publications

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 ...


Anisotropy Of Zigzag Chains Of Palladium, P. K. Sahota, Ralph A. Skomski, Axel Enders, David J. Sellmyer, Arti Kashyap Jan 2011

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

Axel Enders Publications

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 ...


Substrate Dependent Buffer-Layer Assisted Growth Of Nanoclusters, Jan Honolka, Violetta Sessi, Jian Zhang, Simon Hertenberger, Axel Enders, Klaus Kern May 2010

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

Axel Enders Publications

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 ...


Polarized Neutron Reflectometry Study Of The Magnetization Reversal Process In Yba2cu3o7 /La2/3ca1/3mno3 Superlattices Grown On Srtio3 Substrates, J. Hoppler, H. Fritzsche, V. K. Malik, J. Stahn, G. P. Cristiani, H.-U. Habermeier, M. Rössle, Jan Honolka, Axel Enders, C. Bernhard Jan 2010

Polarized Neutron Reflectometry Study Of The Magnetization Reversal Process In Yba2cu3o7 /La2/3ca1/3mno3 Superlattices Grown On Srtio3 Substrates, J. Hoppler, H. Fritzsche, V. K. Malik, J. Stahn, G. P. Cristiani, H.-U. Habermeier, M. Rössle, Jan Honolka, Axel Enders, C. Bernhard

Axel Enders Publications

Using polarized neutron reflectometry we investigated the reversal of the magnetization of a high-Tc superconductor/ferromagnet superlattice that consists of eight bilayers of YBa2Cu3O7(25.6 nm) /La2/3Ca1/3MnO3(25.6 nm) grown on a SrTiO3 substrate. The measurements were performed during a magnetization hysteresis loop at 5 K. We obtained evidence that the reversal in the vicinity of the coercive field proceeds via the switching of micrometer-sized magnetic domains that are considerably larger than the typical domains of La2/3Ca1/3MnO ...


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 Jan 2010

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 Publications

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 ...


Magnetic Surface Nanostructures, Axel Enders, Ralph A. Skomski, Jan Honolka Jan 2010

Magnetic Surface Nanostructures, Axel Enders, Ralph A. Skomski, Jan Honolka

Axel Enders Publications

Recent trends in the emerging field of surface-supported magnetic nanostructures are reviewed. Current strategies for nanostructure synthesis are summarized, followed by a predominantly theoretical description of magnetic phenomena in surface magnetic structures and a review of experimental research in this field. Emphasis is on Fe- or Co-based nanostructures in various low-dimensional geometries, which are studied as model systems to explore the effects of dimensionality, atomic coordination, chemical bonds, alloying and, most importantly, interactions with the supporting substrate on the magnetism. This review also includes a discussion of closely related systems, such as 3d element impurities integrated into organic networks, surface-supported ...


Magnetic Susceptibility Of Nanoscale Kondo Systems, Ralph Skomski, R. Zhang, Parashu Kharel, Axel Enders, Sy_Hwang Liou, D. J. Sellmyer Jan 2010

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

Axel Enders Publications

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 ...


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, Ján Minár, Hubert Ebert Jan 2010

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, Ján Minár, Hubert Ebert

Axel Enders Publications

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 ...


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 Jan 2010

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 Publications

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 ...


Complex Magnetic Phase In Submonolayer Fe Stripes On Pt(997), Jan Honolka, T. Y. Lee, K. Kuhnke, D. Repetto, V. Sessi, Peter Wahl, A. Buchsbaum, P. Varga, S. Gardonio, C. Carbone, S. R. Krishnakumar, P. Gambardella, M. Komelj, R. Singer, M. Fähnle, K. Fauth, G. Schütz, Axel Enders, K. Kern Jan 2009

Complex Magnetic Phase In Submonolayer Fe Stripes On Pt(997), Jan Honolka, T. Y. Lee, K. Kuhnke, D. Repetto, V. Sessi, Peter Wahl, A. Buchsbaum, P. Varga, S. Gardonio, C. Carbone, S. R. Krishnakumar, P. Gambardella, M. Komelj, R. Singer, M. Fähnle, K. Fauth, G. Schütz, Axel Enders, K. Kern

Axel Enders Publications

Correlations between magnetism and morphology of iron nanostructures of monatomic height on Pt(997) substrates are studied using x-ray magnetic circular dichroism as well as scanning tunneling microscopy and helium scattering. A drastic collapse of the average magnetization by more than a factor of 4 is observed when increasing the iron coverage from 0.1 to 0.2 ML. This effect goes along with a softening of the magnetic anisotropy energy and a gradual reorientation of the magnetic easy axis from in plane to out of plane. The experimental findings together with electronic density-functional calculations suggest the formation of a ...


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 Jan 2008

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 Publications

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 ...


Magnetic Anisotropy Of Deposited Transition Metal Clusters, S. Bornemann, J. Minar, J.B. Staunton, Jan Honolka, Axel Enders, Hubert Ebert Jan 2007

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

Axel Enders Publications

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.


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 Jan 2007

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 Publications

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 ...


Absence Of Local Magnetic Moments In Ru And Rh Impurities And Clusters On Ag(100) And Pt(997), Jan Honolka, K. Kuhnke, L. Vitali, Axel Enders, K. Kern, S. Gardonio, C. Carbone, S. R. Krishnakumar, P. Bencok, S. Stepanow, P. Gambardella Jan 2007

Absence Of Local Magnetic Moments In Ru And Rh Impurities And Clusters On Ag(100) And Pt(997), Jan Honolka, K. Kuhnke, L. Vitali, Axel Enders, K. Kern, S. Gardonio, C. Carbone, S. R. Krishnakumar, P. Bencok, S. Stepanow, P. Gambardella

Axel Enders Publications

The magnetism of quench-condensed Ru and Rh impurities and metal films on Ag(100) and Pt(997) has been studied using x-ray magnetic circular dichroism. In the coverage range between 0.22 and 2.0 ML, no dichroic signal was detected at the M3,2 absorption edges of Ru on Ag(100) at a temperature of 5 K in the presence of an applied magnetic field. The same was found for coverages between 0.12 and 0.5 ML of Rh on Ag(100) and Pt(997). It is concluded that the magnetic moments of single impurities, small clusters ...


Magnetism Of Fe Clusters And Islands On Pt Surfaces, D. Repetto, Jan Honolka, S. Rusponi, H. Brune, Axel Enders, Klaus Kern Jan 2006

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

Axel Enders Publications

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.


Magic Alkali-Fullerene Compound Clusters Of Extreme Thermal Stability, Axel Enders, N. Malinowski, D. Ievlev, E. Zurek, Jochen Autschbach, Klaus Kern Jan 2006

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

Axel Enders Publications

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 ...


Structure And Magnetism Of Atomically Thin Fe Layers On Flat And Vicinal Pt Surfaces, D. Repetto, T. Y. Lee, S. Rusponi, Jan Honolka, K. Kuhnke, Violetta Sessi, Ulrich Starke, H. Brune, P. Gambardella, C. Carbone, Axel Enders, K. Kern Jan 2006

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

Axel Enders Publications

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 ...


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 Jan 2005

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 Publications

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 ...


Temperature Dependence Of The Magnetism In Fe/Cu(001), Axel Enders, D. Repetto, D. Peterka, Klaus Kern Jan 2005

Temperature Dependence Of The Magnetism In Fe/Cu(001), Axel Enders, D. Repetto, D. Peterka, Klaus Kern

Axel Enders Publications

The correlation between morphology and magnetism of ultrathin epitaxial films is investigated by a combined study of variable temperature scanning tunneling microscopy, magneto-optical Kerr effect measurements, and Kerr microscopy under ultrahigh vacuum condition. The magnetization reversal of the films was studied as a function of temperature by imaging the propagation of Bloch domain walls in situ. It is demonstrated on the example of fcc Fe films grown at 120 K on Cu(001) that changes in the morphology of the films during annealing are directly reflected in modified magnetic properties. Competing pinning mechanisms for the domain wall propagation are identified ...


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 Jun 2003

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 Publications

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 (C ...


Temperature Dependence Of The Surface Anisotropy Of Fe Ultrathin Films On Cu(001), Axel Enders, D. Peterka, D. Repetto, N. Lin, Ivan Dmitriev, Klaus Kern Jan 2003

Temperature Dependence Of The Surface Anisotropy Of Fe Ultrathin Films On Cu(001), Axel Enders, D. Peterka, D. Repetto, N. Lin, Ivan Dmitriev, Klaus Kern

Axel Enders Publications

We report an experimental approach to separate temperature dependent reversible and irreversible contributions to the perpendicular magnetic anisotropy of Fe films grown at low temperatures on Cu(001) substrates. The surface anisotropy KS(T) is found to decrease linearly with temperature, causing a thermally induced spin reorientation into the plane. The irreversible shift of the spin reorientation transition and the coercivity of the iron films are directly correlated to the increasing Fe island size during annealing. The increased coercivity is discussed in terms of domain wall energy inhomogeneities provided by the islands.


Combined Kerr Microscope And Magnetic Force Microscope For Variable Temperature Ultrahigh Vacuum Investigations, D. Peterka, Axel Enders, G. Haas, Klaus Kern Jan 2003

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

Axel Enders Publications

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.


Adsorbate And Thermally Induced Spin Reorientation Transition In Low-Temperature-Grown Fe/Cu(001), D. Peterka, Axel Enders, G. Haas, K. Kern Jan 2002

Adsorbate And Thermally Induced Spin Reorientation Transition In Low-Temperature-Grown Fe/Cu(001), D. Peterka, Axel Enders, G. Haas, K. Kern

Axel Enders Publications

Adsorbate and thermally induced changes of the spin reorientation transition in Fe wedges grown at 140 K on Cu(001) substrates are investigated by the magneto-optical Kerr effect and Kerr microscopy. The adsorption of oxygen causes a complete reorientation of the easy axis of magnetization into the film plane. In contrast to that carbon monoxide decreases the critical thickness for the reorientation transition of the film by 0.7 monolayer down to 3.6 monolayers, while films thinner than 3.6 monolayers remain magnetized perpendicularly. These adsorbate-induced changes can be ascribed to a change in the surface magnetic anisotropy. Also ...


Structural Transition In (C60)N Clusters, W. Branz, N. Malinowski, Axel Enders, T. P. Martin Jan 2002

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

Axel Enders Publications

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 ...