S. J. Hermsdoerfer
Kaiserslautern University of Technology
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Featured researches published by S. J. Hermsdoerfer.
Applied Physics Letters | 2009
A. V. Chumak; P. Pirro; A. A. Serga; Mikhail Kostylev; R. L. Stamps; Helmut Schultheiss; K. Vogt; S. J. Hermsdoerfer; B. Laegel; P. A. Beck; B. Hillebrands
Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a Permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatially resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.
Applied Physics Letters | 2009
Dong-Soo Han; Sang-Koog Kim; Jun-Young Lee; S. J. Hermsdoerfer; Helmut Schultheiss; B. Leven; B. Hillebrands
We found by micromagnetic simulations that the motion of a transverse wall (TW)–type domain wall in magnetic thin-film nanostripes can be manipulated via interaction with spin waves (SWs) propagating through the TW. The velocity of the TW motion can be controlled by changes of the frequency and amplitude of the propagating SWs. Moreover, the TW motion is efficiently driven by specific SW frequencies that coincide with the resonant frequencies of the local modes existing inside the TW structure. The use of propagating SWs, whose frequencies are tuned to those of the intrinsic TW modes, is an alternative approach for controlling TW motion in nanostripes.
Applied Physics Letters | 2007
Hans T. Nembach; P. Martín Pimentel; S. J. Hermsdoerfer; B. Leven; B. Hillebrands; S. O. Demokritov
The authors demonstrate the stimulation of the magnetization switching process of a Ni81Fe19 ellipsoid, which is dominated by domain nucleation and propagation, by applying a transverse microwave field. The study of the quasistatic switching behavior under the influence of a microwave field was performed using longitudinal magneto-optic Kerr effect magnetometry. A strong reduction of the coercive field for microwave frequencies between 500 and 900MHz has been observed, which can be attributed to two different mechanisms: microwave stimulated enhancement of domain nucleation and microwave stimulated growth of the reversed domain. The authors prove that heating is not the origin of the reduction of the coercive field.
Journal of Applied Physics | 2008
C. W. Sandweg; N. Wiese; D. McGrouther; S. J. Hermsdoerfer; Helmut Schultheiss; B. Leven; S. McVitie; B. Hillebrands; J. N. Chapman
The formation and field response of head-to-head domain walls in curved permalloy wires, fabricated to contain a single antinotch, have been investigated using Lorentz microscopy. High spatial resolution maps of the vector induction distribution in domain walls close to the antinotch have been derived and compared with micromagnetic simulations. In wires of 10 nm thickness the walls are typically of a modified asymmetric transverse wall type. Their response to applied fields tangential to the wire at the antinotch location was studied. The way the wall structure changes depends on whether the field moves the wall away from or further into the notch. Higher fields are needed and much more distorted wall structures are observed in the latter case, indicating that the antinotch acts as an energy barrier for the domain wall.
Applied Physics Letters | 2009
S. J. Hermsdoerfer; Helmut Schultheiss; Christopher Rausch; Sebastian Schafer; B. Leven; Sang-Koog Kim; B. Hillebrands
We present a mechanism for spin-wave excitation using a pinned domain wall, which is forced to oscillate at its eigenfrequency and radiates spin waves. The domain wall acts as a frequency doubler as the excited spin waves have twice the frequency of the domain wall oscillation. The investigations have been carried out using micromagnetic simulations and enable the determination of the main characteristics of the excited spin waves such as frequency, wavelength, and velocity. This behavior is understood by the oscillation in the perpendicular magnetization, which shows two antinodes oscillating out of phase with respect to each other.
Journal of Physics D | 2008
C. W. Sandweg; S. J. Hermsdoerfer; H. Schultheiss; S. Schäfer; B. Leven; B. Hillebrands
The thermal spin-wave distribution in a Ni81Fe19 stripe with an asymmetric transverse domain wall has been investigated using Brillouin light scattering microscopy. Clear evidence has been found that the existence of the domain wall influences the spin-wave distribution of the thermal modes. The thermal spin-wave modes are quantized due to confinement in the radial direction. They vanish near the domain wall and a new mode evolves inside this complex domain wall structure. This effect is attributed to the change in the effective internal field in the domain wall region. The experimental results agree well with static and dynamic micromagnetic simulations.
Physical Review Letters | 2009
Helmut Schultheiss; X. Janssens; M. Van Kampen; Florin Ciubotaru; S. J. Hermsdoerfer; Björn Obry; A Laraoui; A. A. Serga; L. Lagae; A. N. Slavin; B. Leven; B. Hillebrands
We have investigated the generation of spin waves in the free layer of an extended spin-valve structure with a nanoscaled point contact driven by both microwave and direct electric current using Brillouin light scattering microscopy. Simultaneously with the directly excited spin waves, strong nonlinear effects are observed, namely, the generation of eigenmodes with integer multiple frequencies (2f, 3f, 4f) and modes with noninteger factors (0.5f, 1.5f) with respect to the excitation frequency f. The origin of these nonlinear modes is traced back to three-magnon-scattering processes. The direct current influence on the generation of the fundamental mode at frequency f is related to the spin-transfer torque, while the efficiency of three-magnon-scattering processes is controlled by the Oersted field as an additional effect of the direct current.
ieee international magnetics conference | 2006
P. Martín Pimentel; H. Nembach; S. J. Hermsdoerfer; S. O. Demokritov; B. Leven; B. Hillebrands
In this study quasi-static switching behavior of a Ni81Fe19 ellipsoid (long axis 160mum, short axis 80mum, thickness 10 nm) under the influence of a microwave field by longitudinal magneto-optic Kerr effect magnetometry. The external quasi-static magnetic field is applied parallel to the long axis of the ellipsoid. The uniaxial anisotropy induced during the growth process is also orientated parallel to the long axis of the ellipsoid. The switching behavior of the Ni81Fe19 element is studied by measuring hysteresis curves with an applied microwave field perpendicular to the quasi-static magnetic field. The frequency of the microwave field was varied in the range of 500 MHz to 2.0 GHz in steps of 100 MHz. The microwave power is increased from 3.2 mW to 3.2 W for each frequency, which can be estimated as a field range from 0.2 Oe (3.2 mW) to 7.3 Oe (3.2 W). A strong reduction of the coercive field from 4 Oe to 0.5 Oe is observed in the microwave field range from 2.9 Oe (501.2 mW) to 7.3 Oe (3.2 W) for microwave frequencies between 700 MHz and 900 MHz.
Applied Physics Letters | 2006
P. Martín Pimentel; S. J. Hermsdoerfer; Hans T. Nembach; B. Leven; B. Hillebrands; S. Trellenkamp; S. Wolff
A crossed coplanar waveguide design using polymer insulation layers is developed as a tool to experimentally investigate fast, precessional switching phenomena in view of applications in magnetic random access memory. The photosensitive polymer Cyclotene 4024™ (benzocyclobutene) is used as an electric insulation layer to realize a multilayer sample consisting of several different conducting and insulating layers. We report on the processing of Cyclotene 4024™ multilayers with optimized surface and electric insulating properties after hard cure. The micropatterned impedance matched coplanar waveguides have a bandwidth of 8.5GHz according to −2dB criterion, and for the −3dB criterion the bandwidth exceeds the measurement range of up to 15GHz. These values allow for short rise and fall times of the pulse for ultrafast magnetization dynamics measurements.
Physical Review B | 2011
Hans T. Nembach; K. L. Livesey; Michael Kostylev; Patrica Martin-Pimentel; S. J. Hermsdoerfer; B. Leven; J. Fassbender; B. Hillebrands