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  • 1
    Electronic Resource
    Electronic Resource
    Light-scattering observation of anomalous parametric spin-wave character in subsidiary absorption (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5477-5479 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The technique of Brillouin light scattering has been used for the characterization, in terms of wave number and direction of propagation, of parametric spin waves associated with subsidiary absorption in thin films of yttrium iron garnet. Measurements at 7.99, 8.47, and 9.90 GHz have revealed a spin-wave character consistent with theory, with two notable exceptions. First, the data show no evidence for a predicted flip in the azimuthal propagation angle. Second, the measured magnon wave numbers at high fields are inconsistent with the theoretical values. The wave number and polar angle results imply that the change to low-k spin waves is not a discontinuous transition as indicated by the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342524
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  • 2
    Electronic Resource
    Electronic Resource
    Relaxation in NiFe/Ag giant magnetoresistive devices : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5820-5822 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Giant magnetoresistance was measured as a function of time and device size for patterned NiFe/Ag multilayer films. The sputtered NiFe/Ag multilayers were postannealed at 340 °C for 5 min in order to produce a change in resistivity Δρ/ρ of 5% in a saturating field of 4 kA/m (50 Oe). The microstructure of these films is believed to be discontinuous due to Ag bridging through the NiFe grain boundaries after the anneal. The films were fabricated into rectangular stripes with Au current lead, and then exposed to a magnetic field pulse to measure the time response of the resistance, characterized by a time constant τ, from the relation ΔR(t)=ΔR0e−t/τ. An apparatus was developed to produce a magnetic field pulse up to 8 kA/m (100 Oe) with a turn-on/off time constant of 10 μs. The response of the NiFe/Ag devices saturated quickly with the turn-on step with a time constant nearly equal to that of the field pulse. The response to the turn-off step, however, had a time constant of nearly 300 μs. When the field is first applied, the torque on the magnetic moments quickly aligns the magnetization. When the field is shut off, however, the torque due to the field drops to 0, so interacting magnetostatic fields from the grains and thermal energy dominate the relaxation process. The average time constant depends on the device size and the applied current density. Relaxation may be detrimental for using this type of material for read heads where very high data rates are required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362197
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  • 3
    Electronic Resource
    Electronic Resource
    Local magnetoresistance and point-source excitation of Ni-Fe thin films (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6400-6400 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetoresistive (MR) response was measured in Ni-Fe thin films, representative of the films used in magnetic recording read heads, with sense areas as small as 6×6 μm. For the bulk, central, and edge regions of the film, the MR response was measured as a function of magnitude and angle of a uniform in-plane applied magnetic field. Measurements were made using a four-contact technique which included two scanning microprobes and two orthogonal field sources. The microprobes could be scanned with a resolution of 0.1 μm and positioned separately. The field sources produced a maximum field of 24 kA/m (300 Oe) that could be rotated up to ±15°. From the local MR response, the local magnetic behavior was obtained and compared to micromagnetic theory. The bulk MR response was also measured as a function of position on the film of a microfield source used for point-source excitation. The microfield source was a Fe wire electrochemically etched to a 0.1 μm tip diameter. From these results the local MR sensitivity was determined for the central and edge regions. The sensitivity profile of the film is important in optimizing the design of the device. The large variations observed in the MR response between the central and edge regions as a function of uniform field and point source excitations are indicative of the fact that magnetostatic fields dominate the response in these small structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355363
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  • 4
    Electronic Resource
    Electronic Resource
    Simulating device size effects on magnetization pinning mechanisms in spin valves : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6386-6388 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of magnetostatic interactions on the giant magnetoresistive (GMR) response of NiFe/Cu/NiFe spin valves are studied using an analytical model. The model is applicable to devices small enough for the magnetic layers to exhibit single-domain behavior. Devices having lengths in the track-width direction of 10 μm and interlayer separations of 4.5 nm are studied. Stripe heights are varied from 0.5 to 2 μm. The magnetization of one magnetic layer is pinned by a transverse pinning field that is varied from 0 to 24 kA/m (300 Oe). GMR curves for transverse fields are calculated. At zero external field the magnetization of the layers shows a tendency to align themselves antiparallel in the transverse direction. This results in an offset from the ideal biasing of the device. Broadening of the curves due to shape anisotropy occurs with decreasing stripe height and increasing magnetic layer thickness, and the magnetization in the pinned layer becomes less stable. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362692
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  • 5
    Electronic Resource
    Electronic Resource
    Size effects and giant magnetoresistance in unannealed NiFe/Ag multilayer stripes : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6240-6242 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed giant magnetoresistance (GMR) in unannealed NiFe/Ag multilayer thin-film stripes. Rectangular stripes having constant thickness and a constant 11:1 length-to-width aspect ratio, but varying widths down to 0.5 μm, were measured. Two types of multilayer configurations were tested, a system of five NiFe/Ag bilayers with 5.5-nm-thick Ag spacer layers, and a system of nine bilayers with 4.4-nm-thick Ag layers. In contrast to the characteristic of annealed NiFe/Ag multilayer stripes, the unnannealed stripes produced increasing GMR ratios for decreasing stripe sizes, with the 0.5-μm-wide stripe of the five-bilayer system exhibiting a ΔR/R of 2.5%. Barkhausen noise and response broadening also increased with decreasing stripe size, however. The results are discussed in terms of magnetostatic coupling of the NiFe layers within the stripes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362017
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  • 6
    Electronic Resource
    Electronic Resource
    Toroid magnetometer for high-critical-temperature superconductors (abstract) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5476-5476 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved flux-integration magnetometer was used to measure the magnetization of a toroidal sample of sintered YBa2Cu3Ox high-critical-temperature (high-Tc) superconductor as a function of field amplitude, frequency, and temperature. The sample was wound with copper drive and sense windings, and electronic integration was used to obtain magnetic induction. Drive fields up to 144 kA/m (1800 Oe) were generated with a burst of ac current at 0.1–1000 Hz through the field coil. The integrated wave forms were digitally recorded and manipulated to yield calibrated hysteresis loops of induction B and magnetization M versus field H with no need to correct for demagnetization factor. Several interesting effects were observed in the hysteresis loops, illustrating the usefulness of this high-resolution measurement technique for the study of high-Tc materials. As a function of increasing field amplitude, hysteresis first appears at the lower critical field Hc1 of the intergranular coupling component. There is a change in the slope of the magnetization curve as the grains decouple at higher fields. Above a certain temperature, the grains are decoupled even at the lowest fields. Frequency effects were observed at temperatures just below the transition temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345852
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  • 7
    Electronic Resource
    Electronic Resource
    Anomalous low-frequency butterfly curves for subsidiary absorption and ferromagnetic resonance overlap at 3 GHz (abstract) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5642-5642 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Subsidiary-absorption butterfly curves of spin-wave-instability threshold versus static in-plane field have been obtained for yttrium-iron-garnet (YIG) thin films at 3 GHz. The butterfly curves have been found to be rather anomalous, typically displaying a pronounced dip and a very low minimum threshold. These anomalous features are attributed to the overlap of the subsidiary-absorption field region with ferromagnetic resonance (FMR). First-order instability theory was extended to include the uniform-mode response near FMR. The extended theory yields good fits to the data for reasonable values of the YIG FMR linewidths. The theoretical analysis also shows a predicted flip in the azimuthal propagation angle φk for the unstable spin waves in the region of FMR overlap. With increasing field, there are predicted discontinuous changes in φk from 90 ° to 0 ° and back to 90 ° in the region of FMR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345912
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  • 8
    Electronic Resource
    Electronic Resource
    Anomalous low-frequency butterfly curves for subsidiary and ferromagnetic resonance overlap at 3 GHz (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1569-1573 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Subsidiary absorption butterfly curves of spin-wave instability threshold versus static in-plane field have been obtained for yttrium iron garnet (YIG) thin films at 3 GHz. The butterfly curves have been found to be rather anomalous, typically displaying a pronounced dip and a very low minimum threshold. These anomalous features are attributed to the overlap of the subsidiary absorption field region with ferromagnetic resonance (FMR). First-order instability theory was extended to include the uniform mode response near FMR. The extended theory yields good fits to the data for reasonable values of the YIG FMR linewidths. The theoretical analysis also shows a predicted flip in the azimuthal propagation angle φk for the unstable spin waves in the region of FMR overlap. With increasing field, there are predicted discontinuous changes in φk from 90° to 0° and back to 90° in the region of FMR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347251
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  • 9
    Electronic Resource
    Electronic Resource
    Micromagnetic scanning microprobe system (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 383-389 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the apparatus, instrumentation, and data acquisition techniques which make up the micromagnetic scanning microprobe system (MSMS). This system was developed to study magnetoresistive (MR) thin films used in magnetic recording read heads. It uses a dc, four-probe resistance measurement coupled with two pairs of orthogonal field sources. Voltage contacts to the thin film are made with microprobe tips 0.1 μm in diameter on local edge and central regions of the film. Horizontal and vertical microscopes are used to verify tip placement. Results from magnetoresistance measurements of the dynamic response of a MR read head film are shown to demonstrate system operation and performance. The bulk and local magnetoresistance of a 10 μm×10 μm NiFe thin film was measured as a function of applied field and angle. Significant variations in MR responses were seen across the width of the device because of local domain formation. The MSMS is an effective tool for characterizing the effects of domain formation on the output of a MR read head.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145142
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetostatic effects in giant magnetoresistive spin-valve devices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3935-3937 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on magnetotransport measurements of spin valve films that have been fabricated into rectangular stripes with Au current leads. The spin valve films consisted of two magnetic NiFe layers separated by a nonmagnetic Cu layer. The top NiFe layer was magnetically pinned by a FeMn layer with an effective pinning field of 12 kA/m (150 Oe). After device fabrication, the transport properties changed dramatically as the stripe-height of the device was decreased below 1 μm. Internal demagnetizing fields and magnetostatic interactions between the magnetic layers dominated the magnetic response. These interactions change the biasing point and the linearity, and cause a decrease in sensitivity to field changes. We have developed a simple single-domain rotation model that includes magnetostatic, anisotropy, and exchange interactions to describe the magnetic behavior, from which we calculate the transport response. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117575
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