Dieter Engel

Publications

• 8.38

  Impact points

  Asymmetric magnetization reversal of stripe-patterned exchange bias layer systems for controlled magnetic particle transport.

  Arno Ehresmann, Daniel Lengemann, Tanja Weis, Alla Albrecht, Jannick Langfahl-Klabes, Florian Göllner, Dieter Engel

  Advanced materials (Deerfield Beach, Fla.). 11/2011; 23(46):5568-73.

  Domain wall movement assisted transport of particles: exchange-biased samples with designed stripe-domains show strong stray fields and an asymmetric magnetization reversal. Using these characteristics superparamagnetic particles can be trapped and transported directly on the sample over large-scale... [more] Domain wall movement assisted transport of particles: exchange-biased samples with designed stripe-domains show strong stray fields and an asymmetric magnetization reversal. Using these characteristics superparamagnetic particles can be trapped and transported directly on the sample over large-scale areas. High particle velocities, small external fields, and automatically reduced particle clustering allow broad applicability of this transport method.
• 3.14

  Impact points

  Colloidal domain lithography for regularly arranged artificial magnetic out-of-plane monodomains in Au/Co/Au layers.

  Piotr Kuświk, Arno Ehresmann, Maria Tekielak, Bogdan Szymański, Iosif Sveklo, Piotr Mazalski, Dieter Engel, Jan Kisielewski, Daniel Lengemann, Maciej Urbaniak, Christoph Schmidt, Andrzej Maziewski, Feliks Stobiecki

  Nanotechnology. 03/2011; 22(9):095302.

  Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, ... [more] Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He(+) ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states.

• Thermal exchange bias field drift in field cooled Mn83Ir17/Co70Fe30 thin films after 10 keV-He ion bombardment

  Arno Ehresmann, Christoph Schmidt, Tanja Weis, Dieter Engel

  J. Appl. Phys. 01/2011; 109:023910.

  The thermal exchange bias field drift of sputter deposited Mn83Ir17(15 nm)/Co70Fe30(10 nm)/Ta thin films at room temperature after 10 keV He+ ion bombardment in an externally applied in-plane magnetic field for different ion fluences was studied. Although field cooling of the layer system resulted i... [more] The thermal exchange bias field drift of sputter deposited Mn83Ir17(15 nm)/Co70Fe30(10 nm)/Ta thin films at room temperature after 10 keV He+ ion bombardment in an externally applied in-plane magnetic field for different ion fluences was studied. Although field cooling of the layer system resulted in a temporally stable exchange bias field at room temperature the exchange bias field starts to drift after ion bombardment like in non-annealed samples. Between 1 and 648 h after ion bombardment a logarithmic increase in the absolute magnitude of the exchange bias field is observed. A tentative model is presented for its description based on noninteracting domains in the antiferromagnet. A comparison between experimental data and the model reveals the delicate interplay between the ion bombardment modified average antiferromagnetic anisotropy constants, exchange coupling constants, and relaxation time distributions in the polycrystalline layer system influencing the thermal drift velocities.
• 7.33

  Impact points

  Domain-wall movement control in Co/Au multilayers by He(+)-ion-bombardment-induced lateral coercivity gradients.

  M Urbaniak, P Kuświk, Z Kurant, M Tekielak, D Engel, D Lengemann, B Szymański, M Schmidt, J Aleksiejew, A Maziewski, A Ehresmann, F Stobiecki

  Physical review letters. 08/2010; 105(6):067202.

  Defined perpendicular anisotropy gradients in the Co sublayers of a [Co(0.6  nm)/Au(2  nm)](3) sputter-deposited multilayer have been introduced by light ion bombardment through a wedged Au stopper layer. Within such a layer system, domain walls between up- and down-magnetized areas are controllably... [more] Defined perpendicular anisotropy gradients in the Co sublayers of a [Co(0.6  nm)/Au(2  nm)](3) sputter-deposited multilayer have been introduced by light ion bombardment through a wedged Au stopper layer. Within such a layer system, domain walls between up- and down-magnetized areas are controllably movable by an external perpendicular homogeneous magnetic field. This method and layer system is very promising for a controlled magnetic particle transport within the stray fields of the moving domain walls.

• Hyper-domains in exchange bias micro-stripe pattern

  K. Theis-Broehl, A. Westphalen, H. Zabel, U. Ruecker, J. McCord, V. Hoeink, J. Schmalhorst, G. Reiss, T. Weis, D. Engel, A Ehresmann, B.P. Toperverg

  03/2008;

  A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr microscopy and polarized neutron reflectometry, was applied to study the field induced evolution of the magnetization distribution over a periodic pattern of alternating exchange bias stripes. The lateral structure is impr... [more] A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr microscopy and polarized neutron reflectometry, was applied to study the field induced evolution of the magnetization distribution over a periodic pattern of alternating exchange bias stripes. The lateral structure is imprinted into a continuous ferromagnetic/antiferromagnetic exchange-bias bi-layer via laterally selective exposure to He-ion irradiation in an applied field. This creates an alternating frozen-in interfacial exchange bias field competing with the external field in the course of the re-magnetization. It was found that in a magnetic field applied at an angle with respect to the exchange bias axis parallel to the stripes the re-magnetization process proceeds via a variety of different stages. They include coherent rotation of magnetization towards the exchange bias axis, precipitation of small random (ripple) domains, formation of a stripe-like alternation of the magnetization, and development of a state in which the magnetization forms large hyper-domains comprising a number of stripes. Each of those magnetic states is quantitatively characterized via the comprehensive analysis of data on specular and off-specular polarized neutron reflectivity. The results are discussed within a phenomenological model containing a few parameters which can readily be controlled by designing systems with a desired configuration of magnetic moments of micro- and nano-elements. Comment: 11 pages, 7 figures
• 1.06

  Impact points

  Modification of the exchange bias effect by He ion irradiation

  A. Mougin, T. Mewes, R. Lopusnik, M. Jung, D. Engel, A. Ehresmann, H. Schmoranzer, J. Fassbender, B. Hillebrands

  Magnetics, IEEE Transactions on. 10/2000;

  FeNi/FeMn exchange bias samples with a large exchange bias field at room temperature have been prepared. Upon irradiation with He ions, both the exchange bias field and the coercive field are modified. For low ion doses the exchange bias field is enhanced by about 70%. Above a threshold dose of 0.3·... [more] FeNi/FeMn exchange bias samples with a large exchange bias field at room temperature have been prepared. Upon irradiation with He ions, both the exchange bias field and the coercive field are modified. For low ion doses the exchange bias field is enhanced by about 70%. Above a threshold dose of 0.3·1¹⁵ ions/cm², the exchange bias field decreases continuously as the ion dose increases. The observed modifications can be explained in terms of defect creation acting as pinning sites for domain walls and atomic intermixing

• Exchange-bias instability in a bi-layer with an ion beam imprinted stripe pattern of ferromagnetic/antiferromagnetic interfaces

  K. Theis-Bröhl, M. Wolff, A. Westphalen, H. Zabel, J. McCord, V. Höink, J. Schmalhorst, G. Reiss, T. Weis, D. Engel, A Ehresmann, U. Rücker, B. Toperverg

  This version is available at the following Publisher URL: http://prb.aps.org

• Magnetization reversal of exchange bias double layers magnetically patterned by ion irradiation

  J. Fassbender, S. Poppe, T. Mewes, A. Mougin, B. Hillebrands, D. Engel, M. Jung, A Ehresmann, H. Schmoranzer, G. Faini, K.J. Kirk, J.N. Chapman

  He⁺ion irradiation is an excellent tool to modify the magnitude and direction of the exchange bias field on the sub- micrometer scale without affecting the sample topography. This effect has been utilized to magnetically pattern NiFe/FeMn exchange bias double layers using resi... [more] He⁺ion irradiation is an excellent tool to modify the magnitude and direction of the exchange bias field on the sub- micrometer scale without affecting the sample topography. This effect has been utilized to magnetically pattern NiFe/FeMn exchange bias double layers using resist masks patterned by electron beam lithography. Ion irradiation through the masks leads to a local modification of the magnetization reversal behavior and allows to study the magnetization reversal as a function of the exchange bias field strength and the pattern dimensions on a single sample. Results are presented on the macroscopic and microscopic magnetization reversal using the magneto-optic Kerr effect and Lorentz microscopy.