T. Martin

Universität Regensburg, Regensburg, Bavaria, Germany

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Publications (6)14.83 Total impact

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    ABSTRACT: Time-resolved x-ray magnetic circular dichroism was used to investigate ferromagnetically coupled CoFe/Ru/NiFe bilayers. The magnetization dynamics was driven by a continuous wave excitation. The precessional motion of the individual layers was detected separately by tuning the x-ray photon energy to the L<sub>3</sub> absorption edge of either Ni or Co. Using two different waveguide stack geometries in-phase and antiphase excitation could be selected showing its effect in the measured precessional signal of the individual layers. In exchange-coupled bilayer two precessional modes were observed for each layer. The relative phase angles of the magnetic response between the two layers were found to be 8° and 133°, for the two modes revealed their quasiacoustic and quasioptic character.
    Journal of Applied Physics 05/2009; · 2.21 Impact Factor
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    ABSTRACT: The magnetization dynamics of each layer of interlayer exchange coupled Ni <sub>81</sub> Fe <sub>19</sub>/ Ru (t)/ Co <sub>90</sub> Fe <sub>10</sub> films was investigated by time resolved x-ray magnetic circular dichroism (TR-XMCD) after pulsed excitation. The coupling was changed from ferromagnetic to antiferromagnetic by variation of the Ru thickness t . The precessional motion of the individual layers was detected separately by measuring the XMCD signal at the L<sub>3</sub> absorption edge of either nickel or cobalt. From the observation of two frequency components in the precession of both layers in samples with negligible interlayer exchange coupling, the presence of a different coupling mechanism was concluded. Using two different sample geometries, the influence of antiphase and in-phase excitation on the triggered dynamics was studied.
    Journal of Applied Physics 05/2008; · 2.21 Impact Factor
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    ABSTRACT: Vector network analyzer ferromagnetic resonance spectroscopy (VNA-FMR) is used here to study the different excited modes of sputtered asymmetrical NiFe(13.6 nm)/Ru(d(Ru))/NiFe(27.2 nm) exchange-coupled films with variable Ru thicknesses. The obtained results have been compared to those of the symmetrical NiFe( 30 nm)/Ru( dRu)/NiFe( 30 nm). In both cases, the measurements show the existence of an optic and an acoustic precessional mode. The optic mode was only observed over limited field ranges, especially in the symmetrical trilayers. To overcome such a limitation, we developed a new technique similar to the longitudinal FMR, where the bias and the rf field are parallel to each other and perpendicular to the pinning field. Interestingly, and in contrast to the symmetrical trilayers, we observed a mode anti-crossing in the dispersion relation of the asymmetrical layers that we attributed to the thickness difference between the two NiFe layers. Our experimental results on the effect of the biquadratic coupling on the mode frequency variations are in good agreement with the theory.
    Journal of Physics Condensed Matter 01/2008; · 2.22 Impact Factor
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    ABSTRACT: Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR), as well as quasistatic methods such as a magneto-optic Kerr effect magnetometer and a vibrating sample magnetometer, have been used for complementary studies of interlayer exchange coupled Si / Ta / Ni Fe (30 nm )/ Ru (t)/ Ni Fe (30 nm )/ Ta films of variable Ru thickness t . The coupling constants were determined from the measured magnetization curves by fitting them to simulated ones. The dynamics measurements revealed two spin wave modes, which could be identified as optical and acoustical ones. The optical mode changes significantly with the coupling, whereas the slight change of the acoustical mode is due to different relative orientations of the layer magnetizations. Numerical simulations helped to identify optical and acoustical modes. The intensity of these two modes changes with the bias field and coupling. Using VNA-FMR the optical mode could be observed up to higher bias fields than with the PIMM at small excitation angles. While varying the pulse field up to 150 Oe using the PIMM, the intensity ratio of optical and acoustical modes changed and additional modes occurred.
    Journal of Applied Physics 06/2007; · 2.21 Impact Factor
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    ABSTRACT: Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR) have been used for complementary studies of the various excited modes in exchange-coupled NiFe(30 nm)∕Ru(dRu)∕NiFe(30 nm) films with variable Ru thicknesses dRu. For antiferromagnetically coupled layers, two modes, which vary in their relative intensity as a function of the bias field, are detected. These two modes, which are observable simultaneously over a limited range of the bias field with PIMM, are identified as optic and acoustic modes. The mode frequencies and the interlayer exchange coupling are found to oscillate as a function of the Ru layer thickness with a period of 8.5 Å. The frequency oscillations of the optic mode are coupling dependent, while those of the acoustic mode are indirectly related to coupling via the canting angle of the layer magnetizations below the saturation. Comparison between PIMM and VNA-FMR in terms of frequency of modes shows good agreement, but the optic mode is observed over a wider field range with VNA-FMR. Furthermore, we clearly observed different behaviors of the FMR linewidths as a function of the spacer thickness for the optic and acoustic modes. In addition, perpendicular standing spin waves have been studied as a function of coupling. The FMR linewidth of the different modes increases with the microwave frequency and typical damping constants of α=0.0073 have been measured. The effect of the pulse field amplitudes on the properties of the various excited modes has been simulated and studied experimentally.
    Physical review. B, Condensed matter 01/2007; 76(10). · 3.77 Impact Factor
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    ABSTRACT: A pulsed inductive microwave magnetometer (PIMM) is used to examine magnetization dynamics. The thin film sample is brought into close proximity to the coplanar waveguide, which allows for simple changing of samples. The angle between the easy axis (e.a.) and field direction can easily be varied by rotation of the sample on the waveguide. The magnetization dynamics, i.e., precessional frequency, decay time, and precessional amplitude, are determined with respect to this angle or the bias field for epitaxial Fe1-xCox films with different anisotropies. The two precessional motions of a magnetic double layer (FeCo/Au/Ni80Fe20) where resolved with the PIMM, which is promising for future investigations on exchange coupled layers.
    Journal of Applied Physics 01/2005; 97. · 2.21 Impact Factor