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  • 1
    Digitale Medien
    Digitale Medien
    High field effective linewidth and eddy current losses in moderate conductivity single crystal Zn-Y hexagonal ferrite at 10–35 GHz (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 432-442 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The microwave losses associated with the extreme high field tail region of the ferromagnetic resonance (FMR) absorption curve for 0.08- to 1.38-mm-thick c-plane circular disks of single crystal Zn-Y hexagonal ferrite materials with planar anisotropy were investigated at 10, 19.3, and 35.3 GHz, with the static external magnetic field applied in plane. Analysis of the data in terms of magnetic losses only gave anomalous high field effective linewidth ΔHF results; this ΔHF showed a substantial increase with the field, changed with both disk thickness and radius, and was higher for an out-of-plane microwave field direction than for an in-plane direction. This linewidth did scale with the square of the disk thickness, one indication of predominant eddy current losses. The data were then analyzed in terms of eddy current losses, based on the assumption of an insulator FMR response and a high field eddy current loss absorption tail driven by that response. The predictions of the model were in good agreement with the data. Fits to the data gave reasonable and consistent values of the microwave conductivity which ranged from 0.03 to 0.05 Ω−1 cm−1 at 10 GHz to 0.06–0.07 Ω−1 cm−1 at 35 GHz, relative to a measured dc conductivity of 0.02–0.03 Ω−1 cm−1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357093
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  • 2
    Digitale Medien
    Digitale Medien
    Microcantilever torque magnetometry of thin magnetic films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5995-5997 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have developed a microcantilever torque magnetometer based on a torsion-mode atomic force microscope. Thin magnetic films are deposited directly onto micromachined silicon cantilevers. We have measured hysteresis loops of iron thin films with thicknesses ranging from 1 to 40 nm and total magnetic volumes ranging from 2.2×10−11 to 8.8×10−10 cm3. The magnetic moment sensitivity is estimated to be 1.3×10−12 A m2/Hz1/2 at room temperature and ambient conditions. We expect that by operating at the cantilever torsion resonance frequency and at higher torque fields sensitivity will be improved by a factor of 100–1000.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372591
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  • 3
    Digitale Medien
    Digitale Medien
    Modeling of microwave magnetic envelope solitons in thin ferrite films through the nonlinear Schrödinger equation (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3776-3785 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A theoretical analysis of microwave magnetic envelope soliton profiles and the soliton peak power response for high power magnetostatic wave (MSW) excitations in yttrium iron garnet (YIG) thin films has been made. This analysis was based on the standard nonlinear Schrödinger equation with all key parameters based on experiment. The measurements were done for magnetostatic backward volume waves in a 10.2 μm YIG film, with a band edge at 5.06–5.07 GHz and operating point frequencies from 4.80 to 5.00 GHz. The use of accurate dispersion and group velocity parameters and the transmitted power versus frequency response of the MSW signal was critical. It was possible to accurately model both the shapes of the soliton pulses and the peak output versus peak input power response over a wide range of power levels. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368556
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  • 4
    Digitale Medien
    Digitale Medien
    Nonlinear magneto-optic measurement of flux propagation dynamics in thin Permalloy films (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1066-1073 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Time-resolved nonlinear optics are used to study the propagation of magnetic flux pulses in a 250 nm Permalloy film. The flux is generated in the film by coupling it to a coplanar waveguide structure driven with broadband voltage pulses. Flux pulses propagated in the film with a phase velocity of 4.2×105 m/s and a group velocity of 1.5×105 m/s. Both velocities are consistent with the predictions of Damon–Eshbach theory for magnetostatic surface waves with 200–300 μm wavelengths. Within 100 μm of the excitation source, flux pulses decayed monotonically but with no measurable delay. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1421040
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  • 5
    Digitale Medien
    Digitale Medien
    Micromechanical detectors for local field measurements based on ferromagnetic resonance (invited) (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7086-7090 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ferromagnetic resonance (FMR) measurements were performed on micrometer-size thin-film samples deposited onto a micromechanical cantilever detector. The FMR response is coupled to cantilever motion in one of three ways: (1) By measuring the change in torque on the sample in a uniform field; the FMR precession reduces the static magnetic moment of the sample with a resultant change in torque. (2) By measuring the damping torque acting on the FMR precession. (3) By measuring the energy absorbed in FMR using a bimaterial cantilever as a calorimeter sensor. Our instrument is capable of measuring the FMR response in permalloy samples as small as 2×10−11 cm3 in ambient conditions with a signal-to-noise ratio of 100. In addition we demonstrate that this system can be used as a quantitative scanning probe magnetic field microscope. Using the magnetic field sensitivity of the FMR response in a small ferromagnetic particle, we have achieved 50 A/m field resolution on 20 μm length scales. Both dc fields and microwave fields were imaged. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1354583
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  • 6
    Digitale Medien
    Digitale Medien
    Spin wave instability in single crystal Zn–Y hexagonal ferrite at 8.93 GHz (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4454-4469 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Resonance saturation (RS), subsidiary absorption (SA), and parallel pump (PP) spin wave instability threshold measurements have been made on single crystal easy plane disks of Mn substituted Zn–Y type hexagonal ferrite materials at 8.93 GHz and room temperature. For each configuration, "butterfly curves" of the spin wave instability threshold microwave field amplitude hcrit as a function of the static field applied in the disk plane were obtained. The previous theory for these instability processes was also extended to include planar magnetocrystalline anisotropy and a wave vector k dependent spin wave linewidth, ΔHk. The RS butterfly curve had a characteristic "V" shape with a rounded minimum at the ferromagnetic resonance (FMR) field. The nominal ΔHk needed to fit the data at the ferromagnetic resonance field was 7 Oe, but the butterfly curve shape indicated a k-dependent ΔHk. The butterfly curves for the PP configuration were flat at low field and then diverged rapidly at the cutoff field for first order instability processes, Hcut. The SA butterfly curves were also flat over the field interval for first order processes, but then decreased as the field was increased above Hcut. This decrease is attributed to the onset of second order processes due to the proximity of the FMR and additional magnetostatic mode peaks as one moves to and then above Hcut. The flat portions of the PP and SA butterfly curves could be fitted with a single k-independent ΔHk value of 18 Oe. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1352689
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  • 7
    Digitale Medien
    Digitale Medien
    High-field effective linewidth and eddy current losses in moderate conductivity single-crystal M-type barium hexagonal ferrite disks at 10–60 GHz (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2705-2718 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The losses associated with the high-field tail region of the ferromagnetic resonance (FMR) absorption curve were investigated at 10, 19, 35, and 60 GHz for 0.10–1.75-mm-thick c-plane circular disks of flux-grown single-crystal M-type barium ferrite materials. A conventional high-field effective linewidth analysis of the data yielded an effective linewidth which increased with the square of the disk thickness and linearly with frequency, dependencies which indicate a predominant eddy current loss process. Based on these results, an eddy current loss analysis of the tail region was done, based on the insulator FMR response and eddy current losses driven by the FMR response. This analysis leads to a new noninvasive technique for the determination of the microwave conductivity in moderate conductivity ferrites. One obtains the conductivity from an appropriate analysis of the FMR absorption tail in the same way that analysis of the magnetic loss tail yields a high-field effective linewidth. Based on this technique, the microwave conductivity of these flux-grown barium ferrite single-crystal materials was determined as a function of frequency and found to increase linearly from 0.033±0.004 Ω−1 cm−1 at 10 GHz to 0.10±0.02 Ω−1 cm−1 at 60 GHz. These results are consistent with a measured dc conductivity of 0.03–0.05 Ω−1 cm−1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.354665
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  • 8
    Digitale Medien
    Digitale Medien
    Spin–wave instability measurements in Mn substituted single-crystal Zn2Y hexagonal ferrite thin disks at 8.9 GHz (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4883-4883 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Large magnetocrystalline anisotropy makes hexagonal ferrites attractive for microwave and millimeter wave applications. Critical to such applications is the response at high power levels. Relatively little work has been reported in this area. In order to characterize this response, the minimum microwave field amplitude required to excite spin–wave instability, hcrit, is measured for various field–sample configurations. Plots of hcrit versus static field H, termed "butterfly" curves, are then used to obtain spin wave linewidths and define operational power limits for device applications. Two regimes were studied in this work: (1) saturation of the ferromagnetic resonance (FMR) absorption; and (2) parallel pumping instability for fields well below FMR. The objective was to measure butterfly curves and use the results to determine values of the spin–wave linewidth ΔHk. The measurements were made on a 1.2 mm diam 0.15 mm thick single-crystal Mn substituted Zn2Y (Y-type) hexagonal ferrite c-plane (001) disk with easy plane anisotropy. The static field and the 4 μs wide, 30 Hz pulsed microwave field at 8.9 GHz were applied in the plane of the disk. Standard cavity techniques were used. The low power ferromagnetic resonance (FMR) linewidth was 15 Oe. For resonance saturation, the measured hcrit was 0.29 Oe at the FMR field of 775 Oe. The resonance saturation butterfly curve was asymmetric about its minimum value at FMR. The hcrit for parallel pumping was approximately 5 Oe and independent of H over the range of 150–350 Oe. These data and spin–wave instability theory were used to estimate ΔHk values. For parallel pumping, ΔHk was determined to be 17 Oe for the critical modes at one half the 8.9 GHz pump frequency. For resonant saturation, ΔHk was determined to be 12 Oe for the critical modes at the pump frequency. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.364890
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  • 9
    Digitale Medien
    Digitale Medien
    Propagation properties of microwave magnetic envelope solitons in thin yttrium–iron–garnet films at 5 GHz (abstract) : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4879-4879 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Microwave magnetic wave packets propagating in thin yttrium–iron–garnet (YIG) films show potential for novel devices as well as improved understanding of the basic properties of linear and nonlinear waves. The propagation characteristics of these excitations that have been studied up to now, however, do not provide a clear separation between linear and soliton regimes or a clear separation of the different contributions to the decay during propagation. The objective of this work was to study such characteristics for 5 GHz, 13–40 ns wide backward volume wave (BVW) magnetostatic wave square pulses in both the low-power linear and in the high-power soliton regimes and address these issues. The measurements were made with a delay time structure with a long and narrow 7.2 μm thick YIG film and 50 μm wide transducers, and input powers from 5 mW to 2 W. The output peak power Pout versus input pulse power Pin exhibits the same nonlinear response reported previously,1 with a linear response region A followed by a region B response with a more rapid increase in Pout and a high power region C in which Pout goes through a maximum and decreases. However, the integrated output pulse power, or pulse energy, is a strictly linear function of input pulse power over both the A and the B regions. At the same time, one finds a small but measurable increase in the average propagation velocity for the pulses as power is increased. The measured decay in the total pulse energy with propagation time leads to an unambiguous separation of the decay contributions due to dispersion and loss. This allows, in turn, a clear separation between the linear pulse and soliton regimes. The results were modeled from the nonlinear Schrödinger (NLS) equation with propagation and damping terms included. Agreement is good for regions A and B but the NLS model fails completely for region C.© 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.364865
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  • 10
    Digitale Medien
    Digitale Medien
    Angle dependence of the ferromagnetic resonance linewidth and two magnon losses in pulsed laser deposited films of yttrium iron garnet, MnZn ferrite, and NiZn ferrite (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 7838-7848 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Shorted waveguide ferromagnetic resonance (FMR) measurements were made at 9.5 GHz for pulsed laser deposited yttrium iron garnet (YIG), MnZn ferrite, and NiZn ferrite films with thicknesses of 1.8, 0.5, and 1.5 μm, respectively. The FMR field versus the field angle confirmed the operational assumption of a uniform mode response. For the YIG, the linewidth was 10 Oe when the external field and magnetization vectors were perpendicular to the disk (perpendicular FMR) and increased smoothly to a maximum value of 27 Oe when the field and magnetization were in the film plane (parallel FMR). For the MnZn, the linewidth was 49 Oe at perpendicular FMR, increased with the angle between the film normal and the external field to a broad maximum of 80 Oe at 35°, and then dropped to 65 Oe at parallel FMR. For the NiZn, the linewidth was 310 Oe at perpendicular FMR, increased with the field angle to a broad maximum of 1530 Oe at 45°, and then dropped to 960 Oe at parallel FMR. The linewidths were larger than predicted for reasonable values of the Landau–Lifshitz damping and showed angle dependences which indicated nonintrinsic contributions to the loss. Two magnon scattering was used to model these linewidth differences. The angle dependences of the excess linewidths show qualitative agreement with the two magnon predictions, with inhomogeneity sizes in the submicron range and volume fractions below 1%. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.370595
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