Publications (13)55.36 Total impact
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Dataset: jmmm 307
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Article: Vortex dynamics in Permalloy disks with artificial defects: Suppression of the gyrotropic mode
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ABSTRACT: Source: APPLIED PHYSICS LETTERS Volume: 90 Issue: 6 Article Number: 062506 DOI: 10.1063/1.2437710 Published: FEB 5 2007 The dynamics of magnetic vortices in thin Permalloy disks having artificial defects in the form of small holes at different locations within the disk has been investigated by means of frequency-domain spatially resolved ferromagnetic resonance. It is found that the vortex can be effectively captured by such a defect. Consequently the commonly observed gyrotropic vortex motion in an applied microwave field of 1 mT is suppressed. However, if in addition a static magnetic field of at least 4.3 mT is applied, the vortex core is nucleated from the artificial defect and a modified gyrotropic motion starts again. (c) 2007 American Institute of Physics.Applied Physics Letters 02/2007; 90(6):062506. · 3.84 Impact Factor -
Article: Magnetic vortex core reversal by excitation with short bursts of an alternating field.
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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: Spatially resolved dynamic eigenmode spectrum of Co rings.
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ABSTRACT: The spatially resolved eigenmode spectrum of micrometer-sized Co ring elements has been determined by means of combined vector network analyzer ferromagnetic resonance and time resolved magneto-optic Kerr effect measurements. Up to 5 resonant eigenmodes were observed in the frequency range from 45 MHz to 20 GHz as a function of an external magnetic bias field. A well-defined mode structure was found for the two equilibrium states (vortex and onion) which correspond to distinctive spatial modes. The effect of dynamic inter-ring coupling on the modes in the remanent states was evinced. The experimental results are found to be in good agreement with those of micromagnetic simulations. Our results demonstrate that, in analogy to the well-defined static equilibrium magnetic states of ring elements, the eigenmode spectra of this high symmetry geometry consist of a well-defined and simple mode structure.Physical Review Letters 03/2006; 96(5):057207. · 7.37 Impact Factor -
Article: Analysis of the p53 tumor suppressor gene in rheumatoid arthritis synovial fibroblasts.
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ABSTRACT: To determine whether mutations in the tumor suppressor gene p53 may contribute to the transformed-appearing phenotype of rheumatoid arthritis (RA) synovial fibroblasts. We performed p53 gene mutation analysis using different molecular approaches. Synovial fibroblasts of 10 patients with RA were cultured and RNA and DNA were harvested after 3-5 passages in cell culture. Sequence analysis of all exons of the p53 gene was performed using 3 different techniques: 1) single-strand conformational polymorphism, 2) nonisotopic RNase cleavage assay, and 3) base excision sequence scanning T-scan, followed by sequence analysis of specific gene segments. Although p53 antigen could be detected by immunocytochemistry in numerous cultured fibroblasts, gel electrophoresis analysis of products obtained using all 3 methods and subsequent sequence analysis showed no specific mutation pattern in the genome of the synovial fibroblasts from patients in Germany, including the known "hot spots" within the p53 genome. However, p53 mutations were identified in different clones of 3 additional RA synovial fibroblast populations from the United States. Sequence analysis of the p53 promoter did not reveal mutational base changes. The findings of the study support the hypothesis that the majority of the mutations of the p53 gene observed in RA synovium are not derived from the genome of RA synovial fibroblasts, and that the variability of the mutation pattern reflects, in part, the heterogeneity of the disease.Arthritis & Rheumatism 09/1999; 42(8):1594-600. · 7.87 Impact Factor -
Article: Imaging magnetic excitations in confined magnetic structures
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ABSTRACT: In this paper we revisit some particular aspects concerning the dynamic magnetization of thin Ni80Fe20 discs. In particular we address details of the excitation spectrum of Ni80Fe20 discs subjected to in-plane magnetic cw microwave fields. In this case imaging the dynamic magnetization allows us to estimate the internal magnetic field of the ferromagnetic element. -
Article: Magnetization dynamics of the ferrimagnet CoGd near the compensation of magnetization and angular momentum
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ABSTRACT: Magnetization dynamics in alloys of ferrimagnetic CoGd have been studied in the vicinity of the magnetization and angular momentum compensation point as a function of alloy composition and temperature. In agreement with standard mean-field treatments of the dynamics of the total magnetization we observe an increase of the precessional frequency and the effective damping parameter near the angular momentum compensation point. We demonstrate the consistency of the magnetization dynamics extracted from frequency domain methods such as ferromagnetic resonance and time resolved laser pump-probe measurements. -
Article: Magnetic vortex core reversal by excitation with short bursts of an alternating field
NATURE. 444(7118):461-464. -
Article: Modal spectrum of permalloy disks excited by in-plane magnetic fields
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ABSTRACT: The mode spectrum of 4 micron sized ferromagnetic permalloy disks exhibiting a vortex structure in equilibrium is investigated in detail. Normal modes accessible by in-plane field excitations are examined. By means of spatially resolved techniques using Kerr microscopy we recorded the modal structure of the disks at zero bias field. We employed pulsed and continuous wave excitation. As a result we report on normal modes up to the fifth order. Using inductive and spatially resolved resonance measurements the evolution of the mode spectrum as a function of an external magnetic field was investigated. Quantized modes in longitudinal as well as in transverse direction in the uniform magnetized disks were observed. Good agreement between the experimental results and those from micromagnetic simulations was found.Phys. Rev. B. 73(13). -
Article: Modal spctrum of permalloy disks excited by in-plane magnetic fields
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Article: Magnetization dynamics of the ferrimagnet CoGd near the compensation of magnetization and angular momentum
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Article: Comparison of frequency, field, and time domain ferromagnetic resonance methods
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ABSTRACT: We present vector network analyzer ferromagnetic resonance measurements of epitaxial Fe films having a thickness of 16 monolayers. Our objective is to test the reliability of this novel frequency domain technique with respect to frequency and damping. For this purpose we compare vector network analyzer ferromagnetic resonance to pulsed inductive microwave magnetometry, time resolved magneto-optic Kerr effect (both methods in the time domain), and conventional ferromagnetic resonance (measured in the field domain) in terms of position and width of the ferromagnetic resonance. In addition, we compare the various techniques with respect to the signal to noise ratio of the raw data. All data is obtained using the same well characterized ultrathin magnetic Fe/GaAs (0 0 1) film. Finally, we demonstrate the potential of the vector network analyzer ferromagnetic resonance technique for the investigation of nano-structured magnetic elements having nonuniform magnetization configuration. The absorption spectrum of Permalloy disks with a diameter of 200 nm and a thickness of 15 nm shows up to eight distinct resonance peaks. The spatial structure of the corresponding modes was derived from numerical calculations and reveals that azimuthal modes up to the fifth order have been observed inductively.Journal of Magnetism and Magnetic Materials. -
Article: Vortex dynamics in coupled ferromagnetic multilayer structures
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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.
Top co-authors
Top Journals
- Arthritis & Rheumatism (1)
- Physical Review Letters (1)
- Applied Physics Letters (1)
- Nature (1)
Institutions
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2006–2007
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Universität Regensburg
- Institut für Experimentelle und Angewandte Physik
Regensburg, Bavaria, Germany
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