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Selected Works

Axel Enders

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Articles 1 - 8 of 8

Full-Text Articles in Physics

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 ...


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.


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 ...


Stress Evolution During The Growth Of Ultrathin Layers Of Iron And Iron Silicide On Si(111), D. Sander, Axel Enders, J. Kirschner Aug 2013

Stress Evolution During The Growth Of Ultrathin Layers Of Iron And Iron Silicide On Si(111), D. Sander, Axel Enders, J. Kirschner

Axel Enders

Using a simple optical deflection technique, we measured continuously the mechanical stress during the growth of Fe films of 0.1–1.5 nm thickness on Si(111) in ultrahigh vacuum (UHV). The stress versus coverage dependence is discussed in view of the different growth modes during the various stages of Fe deposition. The deposition of up to 0.3 nm Fe induces a compressive stress of -1 N/m. We assign this stress to the formation of a reactive Fe–Si interface layer with a silicide-like structure. Subsequent Fe deposition at 300 K leads to a small tensile stress ...


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 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 Aug 2013

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 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

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 ...


Temperature Dependence Of The Magnetism In Fe/Cu(001), Axel Enders, D. Repetto, D. Peterka, K. Kern Aug 2013

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

Axel Enders

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 ...