H Brückl

Publications (16)61.34 Total impact

• Article: Artificial cilia of magnetically tagged polymer nanowires for biomimetic mechanosensing.

  P Schroeder, J Schotter, A Shoshi, M Eggeling, O Bethge, A Hütten, H Brückl
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  ABSTRACT: Polymeric nanowires of polypyrrole have been implemented as artificial cilia on giant-magneto-resistive multilayer sensors for a biomimetic sensing approach. The arrays were tagged with a magnetic material, the stray field of which changes relative to the underlying sensor as a consequence of mechanical stimuli which are delivered by a piezoactuator. The principle resembles balance sensing in mammals. Measurements of the sensor output voltage suggest a proof of concept at frequencies of around 190 kHz and a tag thickness of ∼300 nm. Characterization was performed by scanning electron microscopy and magnetic force microscopy. Micromagnetic and finite-element simulations were conducted to assess basic sensing aspects.
  Bioinspiration &amp Biomimetics 12/2011; 6(4):046007. · 1.95 Impact Factor
• Chapter: Magnetic Tunneling Junctions — Materials, Geometry and Applications

  G. Reiss, H. Koop, D. Meyners, A. Thomas, S. Kämmerer, J. Schmalhorst, M. Brzeska, X. Kou, H. Brückl, A. Hütten
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  ABSTRACT: The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunnelling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of these junctions increased dramatically. We will briefly address important basic properties of these junctions depending on the material stacking sequence of the underlying standard thin film system with special regard to complex interdiffusion properties. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co2MnSi, where we obtain up to 100% TMR at low temperature. Next, we discuss scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour down to junction sizes below 0.01 µm2. The last part will give a short overview on field programmable logic circuits made from magnetic tunnelling cells, where we demonstrate the clocked operation of a programmed AND gate.
  12/2006: pages 147-165;
• Article: Magnetic vortex core reversal by excitation with short bursts of an alternating field.

  B Van Waeyenberge, A Puzic, H Stoll, K W Chou, T Tyliszczak, R Hertel, M Fähnle, H Brückl, K Rott, G Reiss, I Neudecker, D Weiss, C H Back, G Schütz
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  ABSTRACT: The vortex state, characterized by a curling magnetization, is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of micrometre size and below. The interplay between the magnetostatic and the exchange energy favours an in-plane, closed flux domain structure. This curling magnetization turns out of the plane at the centre of the vortex structure, in an area with a radius of about 10 nanometres--the vortex core. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. The sense of gyration is determined by the vortex core polarization. Here we report on the controlled manipulation of the vortex core polarization by excitation with small bursts of an alternating magnetic field. The vortex motion was imaged by time-resolved scanning transmission X-ray microscopy. We demonstrate that the sense of gyration of the vortex structure can be reversed by applying short bursts of the sinusoidal excitation field with amplitude of about 1.5 mT. This reversal unambiguously indicates a switching of the out-of-plane core polarization. The observed switching mechanism, which can be understood in the framework of micromagnetic theory, gives insights into basic magnetization dynamics and their possible application in data storage.
  Nature 12/2006; 444(7118):461-4. · 36.28 Impact Factor
• Article: Magnetic particles as markers and carriers of biomolecules.

  H Brückl, M Panhorst, J Schotter, P B Kamp, A Becker
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  ABSTRACT: The detection and manipulation of biomolecules on a common platform is of considerable interest not only for application in devices such as diagnostic tools but also for basic research in biological and medical systems. A promising approach is the utilisation of magnetic particles as markers and carriers for biomolecules. The principle functionality of this approach is demonstrated by the authors. Magnetic particles used as markers can be detected by highly sensitive magnetoresistive sensors resulting in a purely electronic signal. A direct comparison with the standard fluorescence method reveals the advantages of using the magnetic particles. In addition, magnetic particles used as carriers can be manipulated on-chip via currents running through especially designed line patterns. Some current drawbacks and future aspects are discussed. The combination of sensing and manipulating magnetic particles is a promising choice for future integrated lab-on-a-chip systems.
  IEE Proceedings - Nanobiotechnology 03/2005; 152(1):41-6. · 1.82 Impact Factor
• Article: Analysing a magnetic molecule detection system--computer simulation.

  W Schepper, J Schotter, H Brückl, G Reiss
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  ABSTRACT: The detection of single molecules, e.g. in biology is possible by marking the interesting molecules with magnetic beads and detect the influence of the beads on giant magnetoresistance (GMR)/tunnel magnetoresistance (TMR)/spin valve (SV) sensors. The development of suitable multilayers has been studied experimentally as well as theoretically in order to optimize the sensor parameters. A finite difference (FD) method including the usually used contributions to the total energy [exchange, antiferromagnetically (af) coupling, anisotropy and magnetostatic] is used for the simulation with additional contributions to the local field according to the stray fields of the beads. In this work, we will show the results of micromagnetic calculations of the magnetization behavior of GMR/TMR sensors considering also the interaction between the domains in the magnetic layers of the sensor and the bead area. We can present first calculations where the bead particles (signal source) and the magnetic layers (sensor device) are considered as a whole magnetic ensemble.
  Journal of Biotechnology 09/2004; 112(1-2):35-46. · 3.05 Impact Factor
• Article: Detection and manipulation of biomolecules by magnetic carriers.

  M Brzeska, M Panhorst, P B Kamp, J Schotter, G Reiss, A Pühler, A Becker, H Brückl
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  ABSTRACT: The detection and manipulation of single molecules on a common platform would be of great interest for basic research of biological or chemical systems. A promising approach is the application of magnetic carriers. The principles are demonstrated in this contribution. It is shown that paramagnetic beads can be detected by highly sensitive magnetoresistive sensors yielding a purely electronic signal. Different configurations are discussed. The capability of the sensors to detect even single markers is demonstrated by a model experiment. In addition, the paramagnetic beads can be used as carriers for biomolecules. They can be manipulated on-chip via currents running through specially designed line patterns. Thus, magnetic markers in combination with magnetoresistive sensors are a promising choice for future integrated lab-on-a-chip systems.
  Journal of Biotechnology 09/2004; 112(1-2):25-33. · 3.05 Impact Factor
• Article: Comparison of a prototype magnetoresistive biosensor to standard fluorescent DNA detection.

  J Schotter, P B Kamp, A Becker, A Pühler, G Reiss, H Brückl
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  ABSTRACT: We present a comparative analysis of a magnetoresistive biosensor to standard fluorescent DNA detection. The biosensor consists of giant magnetoresistive (GMR) type Cu/Ni(80)Fe(20) multilayers in the second antiferromagnetic coupling maximum. Each of the 206 elements of the magnetoresistive biosensor is patterned into a spiral-shaped line that can cover the area of a typical DNA spot (70 microm diameter). The probe DNA is assembled on top of the sensor elements in different concentrations ranging from 16 pg/microl to 10 ng/microl. Complementary biotin-labeled analyte DNA is hybridized to the probe DNA at a concentration of 10 ng/microl. A number of different commercially available magnetic microspheres are investigated to determine the most appropriate markers. The experimental comparison shows that the relative sensitivity of the magnetoresistive biosensor is superior to the fluorescent detection at low probe DNA concentrations.
  Biosensors and Bioelectronics 06/2004; 19(10):1149-56. · 5.60 Impact Factor
• Article: New materials and applications for magnetic tunnel junctions

  G. Reiss, H. Brückl, A. Hütten, H. Koop, D. Meyners, A. Thomas, S. Kämmerer, J. Schmalhorst, M. Brzeska
  [show abstract] [hide abstract]
  ABSTRACT: Large opportunities in magnetolectronic devices are opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of the junctions increased dramatically. We will briefly address some important basics depending on the material stacking sequence of the underlying thin film system with special regard to the ferromagnetic electrodes. Scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour are considered down to junction sizes below 0.01 μm2. The last part will give a short overview on applications beyond the use of the tunnelling elements as storage cells in MRAMs. This concerns mainly field programmable logic circuits, where we demonstrate the clocked operation of a programmed AND gate. The second ‘unconventional’ feature is the use as sensing elements in DNA or protein biochips, where molecules marked magnetically with commercial beads can be detected via the dipole stray field in a highly sensitive and relatively simple way. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
  physica status solidi (a) 05/2004; 201(8):1628 - 1634. · 1.21 Impact Factor
• Source

  Available from: Michal Kopcewicz

  Article: Magnetic and Mössbauer study of Fe/Si multilayers

  T. Luciński, M. Kopcewicz, A. Hütten, H. Brückl, S. Heitmann, T. Hempel, G. Reiss
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  ABSTRACT: The magnetic and structural properties of Fe/Si multilayers (Mls) have been studied by x-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS) methods. Strong antiferromagnetic (AF) coupling J=−1.93 mJ/m2 accompanied by saturation field of 1.5 T has been found for Si layer thickness dSi=1.4 nm. Magnetic moment measurements of Fe/Si Mls vs Fe thickness revealed that 0.25 nm of Fe per single interface is magnetically inactive. The CEMS spectra recorded at room temperature consist of the Zeeman sextet characteristic of the pure Fe phase (hyperfine field of about 32.8 T) accompanied by two spectral components related to FeSi system: magnetic broad sextet and a quadrupole doublet. The broad sextet could originate from various Fe sites at the interface. The nonmagnetic quadrupole split (QS) doublet is most probably associated with the nonstoichiometric c-Fe1−xSix phase. For larger Si layer thickness (dSi>2 nm) the spectral contribution of the QS doublet increases from 5.7% to about 16%. © 2003 American Institute of Physics.
  Journal of Applied Physics 05/2003; 93(10):6501-6503. · 2.17 Impact Factor
• Article: Spinelectronics and its applications

  G. Reiss, H. Brückl, A. Hütten, J. Schmalhorst, M. Justus, A. Thomas, S. Heitmann
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  ABSTRACT: The discovery of antiferromagnetic coupling in metallic Fe/Cr multilayers by Grünberg has triggered enormous research activities in the area of magnetic thin films. Additionally, the resistance of multilayers in the antiferromagnetic state is higher than in the parallel state at magnetic saturation. This Giant Magneto Resistance is caused by spin-dependent scattering of the conduction electrons in the magnetic layers. For applications, however, moderate saturation fields, tailorable resistance characteristics and good temperature stability are required. Additional opportunities are opened by a similar effect in magnetic tunnel junctions. Here, the tunneling probability depends on the relative orientation of the magnetizations of the electrodes and thus a large dependence of the tunneling current on an external magnetic field can be found. This effect is usually called Tunneling Magneto Resistance and can again be used both for detecting external fields as well as for information storage. Much more possible applications are still ahead, especially after the finding of magnetoelectronic effects in semiconductors. In this contribution, we will sketch basic physics of these effects and give examples for current developments.
  physica status solidi (b) 03/2003; 236(2):289 - 302. · 1.32 Impact Factor
• Article: Direct measurement of the oscillation amplitude and criteria for high-quality images in shear force microscopy

  H. Brückl, F. Matthes, G. Reiss
  Applied Physics A 04/1998; 66:S345-S348. · 1.63 Impact Factor
• Article: Detection and manipulation of biomolecules by magnetic carriers

  M Brzeska, M Panhorst, P.B Kamp, J Schotter, G Reiss, A Pühler, A Becker, H Brückl
  [show abstract] [hide abstract]
  ABSTRACT: The detection and manipulation of single molecules on a common platform would be of great interest for basic research of biological or chemical systems. A promising approach is the application of magnetic carriers. The principles are demonstrated in this contribution. It is shown that paramagnetic beads can be detected by highly sensitive magnetoresistive sensors yielding a purely electronic signal. Different configurations are discussed. The capability of the sensors to detect even single markers is demonstrated by a model experiment. In addition, the paramagnetic beads can be used as carriers for biomolecules. They can be manipulated on-chip via currents running through specially designed line patterns. Thus, magnetic markers in combination with magnetoresistive sensors are a promising choice for future integrated lab-on-a-chip systems.
  Journal of Biotechnology.
• Source

  Available from: uni-bielefeld.de

  Article: Electronic transport in metallic films — a tool for scanning tunneling microscopy investigations

  G. Reiss, H. Brückl
  [show abstract] [hide abstract]
  ABSTRACT: In this contribution, we show, that the evaluation of electronic transport parameters in confined systems can be considerably improved by additional Scanning Tunneling Microscopy (STM) imaging of the limiting surfaces. The thin films which are experimentally available usually show both a mesoscopic and a microscopic (i.e. atomic) surface roughness. These two roughnesses, however, are of well separated magnitudes and therefore can be treated either by classical averaging or by quantum mechanics. In order to ensure reliable STM results, the resolution especially of mesoscopic surface features will be discussed. Provided reasonable STM resolution, the experimental data for the resistivity can be interpreted for the first time with a realistic, two dimensional model for the current transport in thin films. Forthcoming applications concerning the distribution of the potential related to current transport in thin films will be discussed.
  Superlattices and Microstructures 11(2):171-174. · 1.49 Impact Factor
• Article: Magnetization reversal of micropattern Fe bar array: Combination of vector and Bragg magneto-optical Kerr effect measurements

  A. Westphalen, K. Theis-Bröhl, H. Zabel, K. Rott, H. Brückl
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  ABSTRACT: We report on a magneto-optical Kerr effect (MOKE) investigation of alternating wide and narrow Fe bars, forming a two-dimensional periodic array. The magnetization reversal was studied by regular longitudinal Vector-MOKE in specular geometry as well as in Bragg-MOKE geometry, using the diffraction spots from the grating for hysteresis measurements. With Vector-MOKE a two-step switching process for the wide and narrow Fe bars is observed, indicative for a narrow switching field distribution in this array. In addition, hysteresis loops were determined as a function of the diffraction order for the hard and easy axis direction. The loops at different orders of diffraction can qualitatively and quantitatively be described by Fourier transformations of micromagnetic simulations.
  Journal of Magnetism and Magnetic Materials 302(1):181-189. · 1.78 Impact Factor
• Article: Comparison of a prototype magnetoresistive biosensor to standard fluorescent DNA detection

  J Schotter, P.B Kamp, A Becker, A Pühler, G Reiss, H Brückl
  [show abstract] [hide abstract]
  ABSTRACT: We present a comparative analysis of a magnetoresistive biosensor to standard fluorescent DNA detection. The biosensor consists of giant magnetoresistive (GMR) type Cu/Ni80Fe20 multilayers in the second antiferromagnetic coupling maximum. Each of the 206 elements of the magnetoresistive biosensor is patterned into a spiral-shaped line that can cover the area of a typical DNA spot (70 μm diameter). The probe DNA is assembled on top of the sensor elements in different concentrations ranging from 16 pg/μl to 10 ng/μl. Complementary biotin-labeled analyte DNA is hybridized to the probe DNA at a concentration of 10 ng/μl. A number of different commercially available magnetic microspheres are investigated to determine the most appropriate markers. The experimental comparison shows that the relative sensitivity of the magnetoresistive biosensor is superior to the fluorescent detection at low probe DNA concentrations.
  Biosensors and Bioelectronics.
• Source

  Available from: Tolek Tyliszczak

  Article: Vortex dynamics in coupled ferromagnetic multilayer structures

  K. Chou, A. Puzic, H. Stoll, G. Schütz, B. Wayenberge, T Tyliszczak, K Rott, G. Reiss, H Brückl, I. Neudecker, Dieter Weiss, Christian Back
  [show abstract] [hide abstract]
  ABSTRACT: Magnetization dynamics in ferromagnetic multilayer structures was studied by time- resolved transmission x-ray microscopy. A square- shaped 11 m2 trilayer structure consisting of Co20 nm/Cu10 nm /Permalloy Ni80Fe2020 nm was investigated. Each ferromagnetic layer showed a Landau-like domain configuration with a single vortex. A gyrotropic vortex motion was excited by an in-plane magnetic field alternating at a frequency of 250 MHz. The movement of the magnetic vortex in each individual magnetic layer was imaged by taking advantage of the element specificity of the x-ray magnetic circular dichroism. A 180° phase shift between the gyrotropic vortex motion in the Permalloy and the Co layer was observed. This phase shift can be ascribed to the magnetic coupling between the layers.