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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The wall coercivity caused by the magnetic nonuniformity has been studied numerically. The Landau-Lifshits-Gilbert (LLG) equation is integrated by an explicit scheme of the modified Dufort-Frankel method. The computation was carried out for a two-dimensional grid system representing the magnetization direction in a magnetic film plane. Typical magnetic parameters for magneto-optic recording media were assumed. Spatial variations of uniaxial anisotropy were treated as the magnetic nonuniformity. The validity of our numerical approach was demonstrated with preliminary one-dimensional computations, compared to analytical solutions. A wall coercive field of 2.5 kOe was observed for the wall coupling with a pinning site (30-A(ring) width and 360-A(ring) spacing along the wall) of 10 times larger anisotropy compared to the ordinary region. A two-dimensional anisotropy variation (K=106–107 erg/cm3) with a wavelength larger than 60 A(ring) also caused a wall coercivity on the order of 1 kOe, compared to those in magneto-optic recording media. It was also found that a fine pinning site on the order of 100 A(ring) caused a notable coercivity for the bubble domain wall surrounding it.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5474-5476 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The present article reports a geometrically induced magnetoresistance (MR) behavior observed in magnetic strips consisting of a symmetric layer structure with lateral sizes down to 0.2 μm. The MR ratio was markedly improved from 2.8% for an as-grown film of Co(6 nm)/Cu(6 nm)/Co(6 nm) to 4.6% by structuring it into a strip with 0.3 μm width. The parabolic MR behavior observed in the hard-axis direction suggests that the magnetization in the two magnetic layers rotates toward the opposite directions, which can be explained by the magnetostatic interaction between the surface magnetic charges at the pattern edges. The dependence of MR saturation field on the pattern width agrees well with a theoretical prediction based on a coherent rotation model. The MR ratio was markedly increased by the increase of the layer number and the thickness of the magnetic layer, the highest value of 7.8% was obtained for a strip made of [Co(6 nm)/Cu(4 nm)]2Co(6 nm). A linear- and hysteresis-free MR response was performed with an alternative field modulation under a transverse bias field. © 1999 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5359-5361 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear magntoresistance (MR) response of Co/Cu multilayer strips with sub-μm width has been performed with a field sensitivity of sub-Oe. The orthogonal spin orientation for neighboring Co layers is initiated with an additional external field applied along the short axis of the strip. The thickness of the Cu layer was optimized to be 2.1 nm, at which the MR ratio of the as grown sample took a maximum value. The MR ratio of the as-grown film of [Co(2 nm)/Cu(2.1 nm)]3/Co(2 nm)/Cu(2 nm) was 12.4%. The multilayer was patterned into strips with the pattern width w down to 0.2 μm by means of electron beam lithography and Ar ion milling. The measured maximum MR ratio of the strips with w=0.4 and 0.2 μm were 9.3% and 8.2%, respectively. The observed parabolic MR profile shows good agreement with the micromagnetic simulation assuming the symmetric scissors motion of the magnetization in the multilayer. A linear MR response was observed in a giant MR strip with 0.4 μm width by applying alternating external fields, ranged from 0.1 to 10 Oe, under a transverse bias field of 300 Oe. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4225-4226 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A micropipetting device incorporating an ultrasonic pump is described, in which vibration motion on the side surface of a cylindrical piezoelectric vibrator plays the key role. A core tube surrounded by three bearings mounted at the central part of the rotor operates essentially for the pump function. The tube-type pipetting device has the merits of transportation of a minute, highly precise amount of liquid because of the electrically controllable characteristics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5318-5320 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we report a perpendicular spin valve behavior in a microstructured noncoupling magnetic trilayer system of Co/Cu-Cu oxide/Co. The Co thin films having markedly different coercivity Hc were prepared with a vacuum evaporation with electron beam (Hc= 20–30 Oe) and rf sputtering (Hc= 90–260 Oe), which enables the selective switching of the magnetization in the base and counter Co layers. The film surface of the Cu was oxidized by the rf sputter etching, which results in the increase of the resistance for the perpendicular current and enables measurements of the perpendicular spin valve behavior at room temperature. The additional spacer layer of sputtered SiO2 with a contact hole of 5 μm diameter was fabricated with photolithographic method between the bottom Co and the intermediate Cu layer, which defined the current path perpendicular to the film plane. The measured magnetoresistance ratio was 0.85% (dR=7.6 mΩ, R=0.89 Ω) at room temperature. © 1996 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6643-6645 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of externally uniform applied orthogonal and parallel in-plane magnetic fields on the stripe-chopping characteristics and negative vertical Bloch line replication probability have been studied experimentally and by numerical simulation on a 5 μm bubble film. The orthogonal and parallel in-plane fields on the stripe domain were varied from −50 to 50 Oe and −9 to 9 Oe, respectively, to represent actual working device parameters. The numerical simulation results agree with the experimental data, confirming the suppression of horizontal Bloch line nucleation by the external-uniform in-plane fields and the in-plane field components of the chopping conductor. © 1996 American Institute of Physics.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Wall and vertical Bloch line (VBL) coercivity arising from spatial nonuniformity in the material parameters has been investigated for a typical 5-μm bubble garnet film by means of a two-dimensional micromagnetic computation. Two-dimensional sinusoidal modulations in the magnitude of the uniaxial anisotropy were assumed as a model for a compositional nonuniformity. Nonuniformities with a spatial wavelength comparable to the wall width were found to exert the largest pinning effect. The typical computed value for the wall and VBL coercivity were 0.7 and 2.2 Oe, respectively, where 10% variation and wavelength of 0.47 μm were assumed. The tendency, that the VBL coercivity is larger than that for the domain wall, agrees with the experimental results reported previously. The wall and VBL coercivity caused by a nonuniform exchange constant have also been computed and compared to the analytical solutions due to the step-like variation of wall and VBL energies, respectively. The larger VBL coercivity compared to that for the wall was observed for a local modulation with the size less than wall width and period more than 1 μm.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6646-6648 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a spin-valve random access memory, the binary bit states of the storage cell are determined by the magnetization direction in the free magnetic layer. The write operation of a submicron memory cell element has been studied by a micromagnetic computation based on an energy minimization scheme, which aids in the chip design. The magnetization of the binary bit states in the element was found to take a single domain structure having the opposite direction of the long-axis component. The mean long-axis component of magnetization of each binary state was ±0.97 without external fields. The selective switching of the bit state in the element was performed by the write currents applied into the two level conductors overlying the element for various conditions. The influence of the write currents to the neighboring element on a two-dimensional memory array with a 1×1 μm pitch was also simulated, in order to confirm the selective switching of the memory element. It was found that the selective write current amplitude decreased with an increasing assist current amplitude and the range was extended by the large difference of the transverse magnetic field between the selected and neighboring element. The effect of the exchange interaction from the pinned magnetic layer on the write operation was also discussed. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6086-6088 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The successive vertical Bloch line (VBL) write operation has been performed in an as-grown 1-μm bubble material with a flank wall writing scheme. An unwinding VBL pair was nucleated by a domain expanding pulse current (200-mA amplitude, 200-ns pulse width, 8-ns rising edge) applied through a hair-pin type conductor (gap:2.6 μm, width:4 μm). The VBL position was controlled by a local in-plane magnetic field produced by a conductor current of 30 mA and a uniform in-plane magnetic field of 10 Oe. The above operating parameters were adjusted by measuring the collapse field of the stripe domain as a function of the parameters. The increase of bubble collapse field from 442 to 513 Oe in accordance with the number of write operations indicated a successful write operation.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5449-5451 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, we report spin dependent electron transport perpendicular to a ferromagnet/semiconductor/ferromagnet trilayer with the current perpendicular to the plane (CPP) geometry and fabricated by a photolithographic technique. The CPP current was defined with a contact hole of 20 μm diameter produced in a SiO2 spacing layer. A CoPt/S/Co trilayer was used in the present study. Various film deposition methods were studied for optimum performance. A superior hard magnetic property was obtained in rf sputtered CoPt, which results in a well defined selective magnetization switching between CoPt and Co layers. The magnetoresistance (MR) effects have been confirmed by the measurement of MR hysteresis for various semiconductor layers. The values of MR change ΔR at room temperature observed in sputtered Ge (42 nm), evaporated Si (30 nm), and sputtered Si (16 nm) were 0.40 mΩ (R=1.3 Ω), 0.30 mΩ (R=2.4 Ω), and 5.5 mΩ (R=19 Ω), respectively. The magnetron sputtering was found to be a most promising method for producing a pinhole free semiconductor layer of order 20 nm thickness. © 1997 American Institute of Physics.
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