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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6235-6237 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional micromagnetic simulation is carried out for small unshielded magnetoresistive (MR) elements. The response of the magnetization to uniform cycling of a transverse external field is studied. For an isolated element without any bias field, the magnetic response is hysteretic, resulting in noisy MR output. For longitudinal patterned exchange bias, the pinning width has to exceed a critical value to achieve a noise-free response. Increasing the edge biasing angle beyond 45° induces undesirable multidomain activities. Soft adjacent layer (SAL) biasing is investigated by using a dual-layer model. Various exchange biasing schemes of the end regions of the MR and SAL layers have been numerically implemented, and it is seen that symmetric exchange coupling of the edge regions of both layers yields a desirable MR response.
    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 71 (1992), S. 5579-5584 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytic solution to the energy barriers of two interacting single domain particles is presented. Identical volumes and uniaxial anisotropies are assumed with easy axes parallel to an external magnetic field. The locations and heights of the system energy barriers are analytically determined when the line joining the two particles is either parallel or perpendicular to the easy axes and the external field. The lowest energy barriers are saddle points of the energy surface and correspond to reversal modes under thermal agitation. When dipole coupling is not strong, the mode of thermal switching is asymmetric fanning or asymmetric coherent rotation, depending upon the bond angle, rather than symmetric fanning or coherent rotation that occurs at the nucleation field. An effective volume that describes the cooperative effect is calculated and good agreement with the numerical results using the Fokker–Planck equation is obtained. The energy barriers can be used to calculate the superparamagnetic relaxation time constants in the high barrier limit.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5545-5547 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization correlations in thin film media in the presence of a written transition have been studied utilizing numerical micromagnetic simulation. Polycrystalline films are modeled by a hexagonal array of identical grains each with random anisotropy axis orientation. A transition is written in the medium and the positional variance, the stationary cross track correlation, and the nonstationary down track correlation functions are determined by suitable averaging over statistical ensembles.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5992-5994 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Micromagnetic numerical simulations are extended to study domain-wall structures and dynamics in micron-thick Permalloy films with an in-plane anisotropy easy axis. The equilibrium domain-wall structure is a flux-closure vortex elongated along the film thickness direction for films thicker than 2 μm. The dynamics of such a vortex wall under an easy-axis field is studied to yield velocity dependence and wall mass. The effect of eddy current damping is simplified by including a larger damping constant in addition to the intrinsic spin damping. With large damping, the steady-state wall structure is more stabilized under applied fields. Under a hard-axis field, wall structure transitions take place for small damping and low-frequency fields; for large damping and higher-frequency fields, these transformations are more suppressed, and the flux conduction is dominated by magnetization rotations instead of wall motions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6004-6006 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, a micromagnetic model is utilized to study dibits recorded under an almost contact condition. Transitions, which are sharply written at contact, suffer irreversible demagnetization while they leave the recording head. Dibit stability under a small perturbing field is examined. A small dc field and a thin-film edge field are utilized for the perturbing field. It is found that, in contact recording, Mrδ/Hc should be sufficiently small for magnetic pattern stability.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3439-3454 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization correlations in polycrystalline thin-film recording media are studied numerically via a micromagnetic cellular automaton model. Magnetization reversal processes exhibit self-organized criticality with domain patterns characterized by the intergranular exchange and magnetostatic interactions. Cross-track correlation, or domain width, is shown to be only slightly dependent on the state of magnetization. Noise in magnetic recording is related to an integration of the cross-track correlation. This integrated width is shown to increase dramatically with increasing exchange coupling and only slightly with increasing magnetostatic coupling. With no exchange coupling certain values of magnetostatic coupling yield medium noise that is below that of a system with totally noninteracting grains. For uniformly magnetized media correlations in the recording direction are stationary and found to vary in length with coupling strength. Scaling laws show that noise decreases proportional to the grain area in the film plane only if there is no intergranular exchange coupling and if the film thickness is reduced in proportion to the grain planar diameter. A review of relevant noise power relations and spectral measurement analysis is given.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5149-5151 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A micromagnetic study of the effects of cobalt modification on the magnetization reversal of elongated γ-Fe2O3 particles is presented. Equilibrium states and irreversible switching are computed numerically. The undoped particle core is identified as the site for the initial irreversible processes. For certain material parameters this can lead to a core-reversed state. The enhancement and the saturation of the enhancement of the switching field are explained as a function of doping level. Extrapolation of the numerical results suggests that approximately one monolayer of cobalt-ferrite is sufficient to yield significant enhancement of the coercivity.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4730-4732 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization fluctuations of uniformly magnetized media have been measured in sputtered CoP thin films as a function of Cr underlayer thickness. Increasing underlayer thickness from 20 to 400 nm in nine steps yields decreasing magnetization fluctuation noise from 210 nm to about 25 nm, similar to the known decrease of transition noise. For virtually every disk, the noise power dependance on magnetization is well fit by the square of the magnetization versus current loop derivative, (dM/dI)2. Thus, the noise mechanism appears to be a modulation process over the entire series. Analysis of measured magnetization noise spectra yields approximate correlation lengths which decrease with increasing Cr underlayer thickness.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5874-5876 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computer simulation is utilized to follow the dynamic evolution of a one-dimensional Bloch domain wall. The Landau–Lifshitz equation with Gilbert damping is solved with the applied field along the domain magnetization. Walker's solution is verified for the case where the anisotropy field is much larger than the Walker critical field. When the critical field is comparable to the anisotropy field, the wall motion exhibits instability. For an external field lower than the Walker critical field, after some transient behavior, the steady-state Walker-type wall configuration is reached; when the applied field is above the Walker limit, the initial single wall gradually evolves into an odd number of Bloch walls with consecutively opposite senses. Wall motions for soft ferrite material with different dampings are also investigated. For very small damping the stability holds well. However, for medium damping, it is found that below some critical field, smaller than Walker's, the steady-state solution is stable. Above that field, the single wall first develops a frontal wake which enlarges until instability when an odd number of walls form.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5805-5807 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic force microscopy (MFM) has been widely utilized to reveal magnetization distributions by sensing the external magnetic-field distribution very close to the sample. The resolution of MFM is determined by the size of the sensor tip and by the spacing between the tip and the measured sample. A technique is developed to analyze the noise and linearity of a MFM image, and consequently to improve the spatial resolution by reducing the spacing loss. As a demonstration, a series of MFM images of a single permalloy particle is obtained and numerically analyzed. The spacing loss is reduced and a much higher resolution image is obtained.
    Type of Medium: Electronic Resource
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