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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The elaboration of four different sample types, namely, isolated NiFe or Co layers in their Cu environment and full, exchange decoupled, [Cu/NiFe/Cu/Co/Cu] periods with either the Co or NiFe layers in the vicinity of the free surface has allowed for a detailed study of the magnetization process of the constitutive layers of one period of a "hard–soft''-type spin valve. The domain distribution and magnetization fluctuations within domains have been monitored by Kerr microscopy. The experiments point to a strong influence of dipolar coupling on the properties of the soft permalloy layer, with a dramatic increase of the NiFe film coercive field with respect to the corresponding quantity in an isolated NiFe layer. The macromagnetization fluctuations detected in the NiFe layer appear most likely linked to fluctuations of low amplitude occurring in the Co layer in the vicinity of the NiFe coercive field.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 7210-7219 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the process by which the in-plane magnetization of an ultrathin (4–11 ML) epitaxial iron film reverses under the action of an external magnetic field. Kerr effect measurements reveal a small in-plane uniaxial anisotropy superimposed on the cubic magnetocrystalline anisotropy which greatly influences the reversal. In addition, we find that depending upon the field orientation, reversal can proceed either via a "1-jump'' mechanism, by the sweeping of 180° domain walls and which gives a classic square hysteresis loop, or by a "2-jump'' mechanism, by the sweeping of 90° domain walls at two distinct applied field strengths—this gives a more unusual hysteresis loop with two irreversible transitions. We have developed a simple phenomenological energy model which explains how so small a uniaxial anisotropy can play so significant a role in the reversal process. The model explains the two reversal mechanisms and predicts with good experimental agreement which should be observed for different applied field orientations. © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2883-2891 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The technique for optical microscopy, [polarized anisotropic dark-field observation (PADO)], of vertical Néel lines (also called vertical Bloch lines) existing inside the Bloch walls separating magnetic domains in thin epitaxial films of ferrimagnetic garnets (bubble garnets) is studied and applied here. Results of experiments investigating the role of the polarization of light impose severe constraints on the theoretical models. The picture emerging from them excludes a contrast due to light diffracted by the usual magneto-optical effects inside the wall. By varying the angle of incidence of the anisotropic dark-field illuminating beam, line contrast inversions can be obtained. It is shown that the sample's thickness, when well above the wavelength of light, is responsible for that fact. Moreover, to reproduce all line contrast reversals, an effective height which is smaller than the sample's thickness has to be considered for the line structure. A tempting conclusion from this study may be that lines are seen in PADO by means of a wall deformation, the origin of which has to be found.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6982-6984 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on specific examples, we examine the consequence of spin-polarized current injection into confined model micromagnetic configurations, namely a high remanence state known as the S state and a low, though nonzero, remanence state called the Leaf state. Magnetization dynamics is solved in the space and time domain owing to the Landau–Lifshitz–Gilbert equation. It is shown that, within model bounds, the S state is not propitious to fast switching under the sole influence of a polarized current, even if disregarding the current induced field, whereas Leaf state switching characteristics become extremely complex as soon as due account is made for the latter. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6719-6721 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical framework is presented for the solution of the Landau–Lifshitz–Gilbert equation of magnetization motion using a semi-implicit Crank–Nicholson integration scheme. Along with the details of both space and time domain discretizations, we report on the development of a physically based self-consistency criterion that allows for a quantitative measurement of error in dynamic micromagnetic simulations. In essence, this criterion relies in recalculating from actual magnetization motion the imposed phenomenological damping constant. Test calculations were performed with special attention paid to the determination of suitable integration time steps. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3153-3158 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new technique for observing domain walls and lines in materials with perpendicular anisotropy is presented. It employs laser light in a laser scan microscope and uses anisotropic diffraction by the wall/line magnetic structure. The contrast obtained can be understood simply and a numerical computation shows good agreement with experimental results. Wall configurations with numerous lines may be obtained when nucleating parallel stripes upon reduction to zero of a saturating in-plane field.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is proposed that the main source of contrast of vertical Bloch lines (VBLs) in bubble garnets, when viewed by means of anisotropic dark field optical imaging, is a microdeformation of the wall plane at line location. The motive force for wall tilting is the compensation of the monopolar σ charges borne by VBLs. The tilted wall section acts as a phase object and allows for the formation of line images with well-defined symmetries and independent of the incident-beam polarization. All these features agree fully with experimental evidence. An approximate model of the wall deformation is presented and shown to be consistent for a given thickness and material parameters with the results of an ab initio numerical computation of the 3D structure of a VBL. The implications of the microdeformation model in terms of line observability are analyzed and compared with experimental data.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 656-658 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By combining a finite element tip model and numerical simulations of the tip–sample interaction, it is shown that magnetic force microscopy images of patterned soft elements may be quantitatively compared to experiments, even when performed at low lift heights, while preserving physically realistic tip characteristics. The analysis framework relies on variational principles. Assuming magnetically hard tips, the model is both exact and numerically more accurate than hitherto achieved. © 2001 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5315-5317 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The domain morphology in CoPt multilayers has been investigated by means of magnetic force microscopy for a broad range of thickness parameters. Following hard-axis saturation, complex closure domains, isolated reversed domains, and segmented and fully developed stripe patterns are clearly identified down to stripe widths of the order of 50 nm. Pending full numerical simulations, the stripe width behavior versus Co and Pt thicknesses has been confronted to the predictions of a purely magnetostatic model. The data are consistent with the existence of a single and physically realistic characteristic length, which, however, is viewed as mostly casual. Likely reasons are discussed. © 1997 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3849-3851 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Domains were imaged by magnetic force microscopy (MFM) on materials where the domain size exceeds the sample thickness by three orders of magnitude. Selected samples are a magnetooptical medium and ultrathin cobalt films, all with perpendicular magnetization. A strong domain contrast is observed in both cases. This fact is confronted to the usual theory of MFM image formation, in which the stray field from one body (tip or sample) is sensed by the other, without altering of the magnetization distributions. It is shown that the domain contrast in such extreme conditions cannot be explained with that theory. On the contrary, Abraham and McDonald's model, which considers the response of the sample to the tip field, is quantitatively compared to experiment. It is shown to provide a good qualitative description of the results, but not a quantitative one, because of oversimplification. © 1997 American Institute of Physics.
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