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Thu, 17 Sep 2009 18:59:29 +0200Thu, 17 Sep 2009 18:59:29 +0200Spherical Fast Multiscale Approximation by Locally Compact Orthogonal Wavelets
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/2128
Using a stereographical projection to the plane we construct an O(N log(N)) algorithm to approximate scattered data in N points by orthogonal, compactly supported wavelets on the surface of a 2-sphere or a local subset of it. In fact, the sphere is not treated all at once, but is split into subdomains whose results are combined afterwards. After choosing the center of the area of interest the scattered data points are mapped from the sphere to the tangential plane through that point. By combining a k-nearest neighbor search algorithm and the two dimensional fast wavelet transform a fast approximation of the data is computed and mapped back to the sphere. The algorithm is tested with nearly 1 million data points and yields an approximation with 0.35% relative errors in roughly 2 minutes on a standard computer using our MATLAB implementation. The method is very flexible and allows the application of the full range of two dimensional wavelets.Frank Bauer; Martin Guttingpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/2128Thu, 17 Sep 2009 18:59:29 +0200Mode beating of spin wave beams in ferrimagnetic Lu2.04Bi0.96Fe5O12 films
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/878
Absract: We report on measurements of the two-dimensional intensity distribtion of linear and non-linear spin wave excitations in a LuBiFeO film. The spin wave intensity was detected with a high-resolution Brillouinlight scatteringspectroscopy setup. The observed snake-like structure of the spin wave intensity distribution is understood as a mode beating between modes with different lateral spin wave intensity distributions. The theoretical treatment of the linear regime is performed analytically, whereas the propagation of non-linear spin waves is simulated by a numerical solution of a non-linear Schrödinger equation with suitable boundary conditions.Oliver Büttner; Martin Bauer; Christoph Mathieu; Serguei Demokritov; Burkard Hillebrands; P.A. Kolodin; M.P. Kostylev; S. Sure; H. Dötsch; V. Grimalsky; Yu. Rapoport; A.N. Slavinpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/878Fri, 02 Mar 2001 00:00:00 +0100Switching behavior of a Stoner particle beyond the relaxation time limit
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/924
We report results of the switching properties of Stoner-like magnetic particles subject to short magnetic field pulses, obtained by numerical investigations. We discuss the switching properties as a function of the external field pulse strength and direction, the pulse length and the pulse shape. For field pulses long compared to the ferromagnetic resonance precession time the switching behavior is governed by the magnetic damping term, whereas in the limit of short field pulses the switching properties are dominated by the details of the precession of the magnetic moment. In the latter case, by choosing the right field pulse parameters, the magnetic damping term is of minor importance and ultrafast switching can be achieved. Switching can be obtained in an enlarged angular range of the direction of the applied field compared to the case of long pulses.Martin Bauer; Jürgen Fassbender; Burkard Hillebrands; R. L. Stampspreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/924Mon, 03 Apr 2000 00:00:00 +0200Successful suppression of magnetization precession after short field pulses
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/977
For the next generation of high data rate magnetic recording above 1 Gbit/s, a better understanding of the switching processes for both recording heads and media will be required. In order to maximize the switch-ing speed for such devices, the magnetization precession after the magnetic field pulse termination needs to be suppressed to a maximum degree. It is demonstrated experimentally for ferrite films that the appropriate adjustment of the field pulse parameters and/or the static applied field may lead to a full suppression of the magnetization precession immediately upon termination of the field pulse. The suppression is explained by taking into account the actual direction of the magnetization with respect to the static field direction at the pulse termination.Martin Bauer; Radek Lopusnik; Jürgen Fassbender; Burkard Hillebrands; H. Dötschpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/977Fri, 18 Feb 2000 00:00:00 +0100Observation of spatiotemporal self-focusing of spin waves in magnetic films
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/947
The first observation of spatiotemporal self-focusing of spin waves is reported. The experimental results are obtained for dipolar spin waves in yttrium-iron-garnet films by means of a newly developed space- and time-resolved Brillouin light scattering technique. They demonstrate self-focusing of a moving wave pulse in two spatial dimensions, and formation of localized two-dimensional wave packets, the collapse of which is stopped by dissipation. The experimental results are in good qualitative agreement with numerical simulations.Martin Bauer; Oliver Büttner; Serguei Demokritov; Burkard Hillebrands; Y. Grimalsky; Yu Rapoport; Slavin A.N.preprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/947Thu, 10 Feb 2000 00:00:00 +0100Propagation of linear and nonlinear spin wave excitations in YIG and LuBiFeO films studied by space resolved Brillouin light scattering (extended abstract)
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/950
Martin Bauer; C. Mathieu; Serguei Demokritov; Burkard Hillebrands; P.A. Kolodin; S. Sure; H. Dötsch; A.N. Slavinpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/950Thu, 10 Feb 2000 00:00:00 +0100In-plane anomalies of the exchange bias field in Ni80Fe20/Fe50Mn50 bilayers on Cu(110)
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/951
We report on the exchange bias effect as a function of the in-plane direction of the applied field in twofold symmetric, epitaxial Ni 80 Fe 20 /Fe 50 Mn 50 bilayers grown on Cu~110! single-crystal substrates. An enhancement of the exchange bias field, H eb , up to a factor of 2 is observed if the external field is nearly, but not fully aligned perpendicular to the symmetry direction of the exchange bias field. From the measurement of the exchange bias field as a function of the in-plane angle of the applied field, the unidirectional, uniaxial and fourfold anisotropy contributions are determined with high precision. The symmetry direction of the unidirectional anisotropy switches with increasing NiFe thickness from [110] to [001].S Riedling; Martin Bauer; C. Mathieu; Burkard Hillebrands; R. Jungblut; Kohlhepp J.; A. Reinderspreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/951Thu, 10 Feb 2000 00:00:00 +0100Growth and Magnetic Properties of Fe films on vicinal to (001) substrates
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/942
We report on investigations of the crystallographic structure and the magnetic anisotropies of epitaxial iron films deposited onto periodically stepped Ag(001) surfaces using low energy electron diffraction, x-ray diffraction, second harmonic generation (SHG), as well as the Brillouin light scattering (BLS) technique. The focus of the present study lies on the interrelation between the surface morphology of the buffer layers and the magnetic properties of the Fe films, epitaxially grown onto them. Especially the symmetry breaking at the atomic steps is found to create an uniaxial magnetic anisotropy measured by BLS and a very strong anisotropic signal in magnetic SHG.Andre Frank; Jörg Jorzick; Marc Rickart; Martin Bauer; Jörg Fassbender; Serguei Demokritov; Burkard Hillebrands; M. Scheib; A. Keen; A. Petukhov; A. Kirilyuk; Th. Rasingpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/942Wed, 09 Feb 2000 00:00:00 +0100Linear and Nonlinear Diffraction of Dipolar Spin Waves in Yttrium Iron Garnet Films Observed by Space- and Time-Resolved Brillouin Light Scattering,
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/935
A new advanced space- and time-resolved Brillouin light scattering (BLS) technique is used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The new technique is an effective tool for investigations of two-dimensional spin wave propagation with high spatial and temporal resolution. Linear effects, such as the unidirectional exci-tation of magnetostatic surface waves and the propagation of backward volume magnetostatic waves (BVMSW) in two preferential directions due to the non-collinearity of their phase and group velocities are investigated in detail. In the nonlinear regime stationary and non-stationary self-focusing effects are studied. It is shown, that non-linear diffraction of a stationary BVMSW beam, having a finite transverse aperture, leads to self-focusing of the beam at one spatial point. Diffraction of a finite-duration (non-stationary) BVMSW pulse leads to space-time self-focusing and formation of a strongly localized two-dimensional wave packet (spin wave bullet). Numerical modeling of the diffraction process by using a variational approach and direct numerical integration of the two-dimensional non-linear Schrödinger equation provides a good qualitative description of the observed phenomena.Oliver Büttner; Martin Bauer; Serguei Demokritov; Yu.S. Kivshar; V. Grimalsky; Yu. Rapoport; A.N. Slavinpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/935Tue, 08 Feb 2000 00:00:00 +0100Space- and time-resolved Brillouin light scattering from nonlinear spinwave packets
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/938
Oliver Büttner; Martin Bauer; Andreas Rueff; Serguei Demokritov; Burkard Hillebrands; A.N. Slavin; M.P. Kostylevpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/938Tue, 08 Feb 2000 00:00:00 +0100Switching behavior of Stoner-like magnetic thin film elements
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/939
Martin Bauer; Jürgen Fassbender; Burkard Hillebrandspreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/939Tue, 08 Feb 2000 00:00:00 +0100Spatial and Spatio-Temporal Self-Focusing of Spin Waves in Garnet Films Observed by Space- and Time-Resolved Brillouin Light Scattering
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/940
A new advanced space- and time-resolved Brillouin light scattering technique is used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The technique is an effective tool for investigations of two-dimensional spin wave propagation with high spatial and temporal resolution. Nonlinear effects such as stationary and nonstationary self-focusing are investigated in detail. It is shown, that nonlinear diffraction of a stationary backward volume magnetostatic wave (BVMSW) beam, having a finite transverse aperture, leads to selffocusing of the beam at one spatial point. Diffraction of a finite-duration (non-stationary) BVMSW pulse leads to space-time self-focusing and formation of a strongly localized two-dimensional wave packet (spin wave bullet).Oliver Büttner; Martin Bauer; Jürgen Fassbender; Burkard Hillebrandspreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/940Tue, 08 Feb 2000 00:00:00 +0100Brillouin light scattering investigations of exchange biased (110)-oriented NiFe/FeMn bilayers
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/893
All contributing magnetic anisotropies in (110)-oriented exchange biased Ni 80 Fe 20 /Fe 50 Mn 50 double layers prepared by molecular beam epitaxy on Cu(110) single crystals have been determined by means of Brillouin light scattering. Upon covering the Ni 80 Fe 20 films by Fe 50 Mn 50 , a unidirectional anisotropy contribution appears, which is consistent with the measured exchange bias field. The uniaxial and fourfold in-plane anisotropy contributions are largely modified by an amount, which scales with the Ni 80 Fe 20 thickness, indicating an interface effect. The strong uniaxial anisotropy contribution shows an in-plane switching of the easy axis from [110] to [001] with increasing Ni 80 Fe 20 -layer thickness. The large mode width of the spin wave excitations, which exceeds the linewidth of uncovered Ni 80 Fe 20 films by a factor of more than six, indicates large spatial variations of the exchange coupling constant. (C) 1998 American Institute of Physics.Christoph Mathieu; Martin Bauer; Burkard Hillebrands; Jürgen Fassbender; G. Güntherodt; R. Jungblut; J. Kohlhepp; A. Reindersarticlehttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/893Thu, 01 Jan 1998 00:00:00 +0100Direct observation of two-dimensional self-focusing and initial stages of a wave collapse for spin waves inmagnetic films
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/904
The first observation of self-focusing of dipolar spin waves in garnet film media is reported. In particular, we show that the quasi-stationary diffraction of a finite-aperture spin wave beam in a focusing medium leads to the concentration of the wave power in one focal point rather than along a certain line (channel). The obtained results demonstrate the wide applicability of non-linear spin wave media to study non-linear wave phenomena using an advanced combined microwave-Brillouin light scattering technique for a two-dimensional mapping of the spin wave amplitudes.Martin Bauer; Christoph Mathieu; Serguei Demokritov; Burkhard Hillebrands; P.A. Kolodin; S. Sure; H. Dötsch; A. N. Slavinarticlehttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/904Wed, 01 Jan 1997 00:00:00 +0100Anisotropic magnetic coupling of permalloy micron dots forming a square lattice
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/926
Static magnetic and spin wave properties of square lattices of permalloy micron dots with thicknesses of 500 Å and 1000 Å and with varying dot separations have been investigated. A magnetic fourfold anisotropy was found for the lattice with dot diameters of 1 micrometer and a dot separation of 0.1 micrometer. The anisotropy is attributed to an anisotropic dipole-dipole interaction between magnetically unsaturated parts of the dots. The anisotropy strength (order of 100000 erg/cm^3 ) decreases with increasing in-plane applied magnetic field.Christoph Mathieu; Martin Bauer; Oliver Büttner; Steffen Riedling; Björn Roos; Serguei Demokritov; Burkard Hillebrands; C. Hartmann; B. Bartenlian; C. Chappert; D. Decanini; F. Rousseaux; E. Cambril; A. Müller; B. Hoffmann; U. Hartmannarticlehttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/926Wed, 01 Jan 1997 00:00:00 +0100Static and dynamic properties of patterned magnetic permalloy films
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/930
Static magnetic and spin wave properties of square lattices of permalloy micron dots with thicknesses of 500 Å and 1000 Å and with varying dot separations have been investigated. The spin wave frequencies can be well described taking into account the demagnetization factor of each single dot. A magnetic four-fold anisotropy was found for the lattice with dot diameters of 1 micrometer and a dot separation of 0.1 micrometer. The anisotropy is attributed to an anisotropic dipole-dipole interaction between magnetically unsaturated parts of the dots. The anisotropy strength (order of 100000 erg/cm^3 ) decreases with increasing in-plane applied magnetic field.Burkard Hillebrands; Christoph Mathieu; C. Hartmann; Martin Bauer; Oliver Büttner; Steffen Riedling; Björn Roos; Serguei Demokritov; B. Bartenlian; C. Chappert; D. Decanini; F. Rousseaux; E. Cambril; A. Müller; B. Hoffmann; U. Hartmannarticlehttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/930Wed, 01 Jan 1997 00:00:00 +0100