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  • 1
    Electronic Resource
    Electronic Resource
    Micromagnetic studies of inhomogeneous CoPtCr bicrystal thin-film media : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4916-4918 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of medium inhomogeneities in microstructure and exchange configuration are studied by using micromagnetic simulation. Two types of media are studied: one has a uniform bicrystal structure and another has a partial bicrystal structure with 20% random nonbicrystal sites. The comparison of magnetic (M-H loops) and recording properties (transition profiles and noise) for these two types of media are made under two cases with homogeneous or inhomogeneous intergranular exchange coupling. It is found that the introduction of random nonbicrystal sites reduces the medium noise in the case with homogeneous intergranular exchange, while medium noise is barely affected in the case with inhomogeneous intergranular exchange. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361586
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  • 2
    Electronic Resource
    Electronic Resource
    Signals and nonlinearities in thin metal-particle tape : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5661-5663 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new type of metal-particle tape, whose thickness is thinner and whose particles are better oriented than traditional thick particulate media, is simulated and analyzed. Signals at high densities are much larger in the thin tape than in the traditional tape. Nonlinearities at high densities are dominated by transition width increases. Signals and nonlinearities in even thinner media are studied versus record gap length to investigate proper system parameters. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362208
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  • 3
    Electronic Resource
    Electronic Resource
    Nonuniform switching of single domain particles at finite temperatures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4609-4616 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has recently been shown that nonuniform thermal fluctuations are able to significantly reduce the coercivity of elongated ferromagnetic particles compared to the uniform rotation model of Néel and Brown. In particular, this theory revealed that even for particles that are single domain in the remanent state, a nonuniform energy barrier exists which is proportional to the product of the particle cross-sectional area and the domain wall energy. For sufficiently long particles, this energy barrier is therefore always lower than that of uniform reversal. Here, several implications of this theory are discussed. It is shown that the coercivity of a particle with fixed volume decreases with increasing aspect ratio. For a fixed particle shape, the coercivity is lower with decreasing exchange constant. For small particle aspect ratios the theory is shown to merge continuously into the Néel–Brown theory. The angular dependence of the coercivity is evaluated explicitly. The reduction from the Stoner–Wohlfarth value is maximal for external fields parallel and perpendicular to the particle axis and the coercivity shows an asymmetric angular dependence. Both features are in accordance with recent experiments on an elongated single domain particle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355908
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  • 4
    Electronic Resource
    Electronic Resource
    Micromagnetics of GMR spin-valve heads : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6385-6387 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three-dimensional micromagnetic modeling of shielded giant magnetoresistive heads with a spin-valve sensor is presented. If the pinning field from the exchange layer is not large enough, partial unsaturation of the pinned layer occurs upon excitation from the medium, which may cause down-track output noise. Increasing the pinning strength diminishes the playback instability, however, a larger sensor height is then desirable for the ease of proper biasing, but at the expense of on-track signal level. The free layer magnetization is nominally horizontal, reducing off-track asymmetry compared to heads with smaller sensor height.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355358
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental analysis of the effects of tape thickness on magnetic recording : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5658-5660 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Advances in magnetic tape recording have produced media with magnetic layers as thin as 0.1 μm. In this article, a metal particulate tape with a magnetic layer thickness of ∼0.37 μm is compared to a standard thick media tape with a magnetic layer thickness of ∼4 μm. Measurements of the isolated pulse are made and shown to compare well with micromagnetic simulations. The replay voltage versus current is measured with a 4 μm track width, shielded magnetoresistive head at various densities. The thin tape shows better high density response at high currents than the thick tape. The simulations show that the transitions are sharper on the thin tape due to both the reduction in thickness, and an improvement in the particle orientation. The better oriented particles yield narrower pulses, thereby improving the high frequency response of the tape. Frequency response measurements are also taken with the magnetoresistive head, which yield a signal to noise ratio of (approximately-greater-than)20 dB at 200 kfci. Last, overwrite performance versus current is compared for the two tapes plus a metal-evaporated (ME) tape with a 0.2 μm thick layer. A significant improvement in overwrite is seen on the ME tape. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362207
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  • 6
    Electronic Resource
    Electronic Resource
    Noise correlations in dibit recording : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5765-5767 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Medium noise correlations in dibit data patterns have been studied experimentally in thin film disk/head recording systems. An empirical eigenfunction expansion was utilized to identify the dominant noise modes and possible associated physical mechanisms. At large bit separation where noise power adds linearly, dibit in-phase jitter and out-of-phase jitter were found to be the leading noise modes. The noise waveform shape associated with out-of-phase jitter approaches that of the dibit signals (i.e., this mode of noise becomes amplitude-like) as the bit separation is reduced. In addition, dibit amplitude variation due to the interaction between the two pulses generates the same amplitude-like noise for a small dibit separation. Amplitude mode noise increases as the bit separation is reduced, causing the supralinear noise increase in high recording density. Results from nonlinear amplitude reduction measurement in dibit recording indicate a close correlation between the nonlinearities and the supralinear noise enhancement at high recording density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355608
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  • 7
    Electronic Resource
    Electronic Resource
    Micromagnetic studies of medium noise mechanisms : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6779-6781 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a granular thin-film medium, the total noise is determined by intergranular interactions and local anisotropy fields. Among these two factors, the effect of local anisotropy on medium noise is relatively less clear. A micromagnetic model is used to study four kinds of media with different anisotropy distributions. Perpendicular anisotropy is examined in two of the four media: One has a uniform perpendicular component for all grains, the other has some perpendicular grains randomly distributed. It is found that if exchange coupling is absent, the medium with the most uniformly distributed crystalline anisotropy has the lowest noise. Otherwise, the medium with the most nonuniformly distributed anisotropy yields the lowest noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356827
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental studies of nonlinearities in MR heads : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5883-5885 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetoresistive (MR) heads have been widely developed for high density digital magnetic recording. The nonlinear MR head response causes nonlinear distortion in the playback signals, and this results in a degradation of system performance. In this work, techniques for identifying the nonlinearity due to the playback process have been developed. Different levels of nonlinear distortion in the playback signals were observed for different head/disk combinations. The behavior of the MR nonlinear distortion as a function of flying height and recording density was also examined. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362161
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  • 9
    Electronic Resource
    Electronic Resource
    Micromagnetic modeling of magnetic anisotropy in textured thin-film media (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6411-6415 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Existing micromagnetic models, based on single domain grains that individually follow coherent rotation during reversal, have been utilized to study the effect of various texture-induced microstructures on the hysteretic behavior of Co-alloy thin films with circumferentially textured substrates. The roles of preferential orientation of Co c axes, grain elongation, and segregation, as well as possible short-range intergranular coupling, have been examined in an effort to understand the origins of widely observed magnetic anisotropy in these media. Preferential c-axis distribution along the track direction yields reasonable remanences and coercivities for both circumferential and radial loops, but the observed loop closure remains unaccounted for by c-axis distribution alone. Closely packed arrays of elongated grains maintain relative isotropy in terms of magnetostatic interactions, while voids along texture lines contribute to the magnetostatic anisotropy of the film. The limitations of the model are also discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359114
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  • 10
    Electronic Resource
    Electronic Resource
    Ferromagnetic switching in elongated γ-Fe2O3 particles (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5832-5834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of numerical micromagnetic calculations of the switching process in elongated γ-Fe2O3 particles are reported. The particles are represented by square rectangular prisms of aspect ratio 3:1 and 5:1, respectively. The crystalline anisotropy is cubic with K1=−4.6×104 erg/cm3 and with the [110] direction in the long particle axis. The application of a reverse field leads to formation of vortices at the ends of the particle. As the reverse field is increased in magnitude the vortices expand from the ends of the particle inwards. Equilibrium and transient magnetization states are computed as a function of particle size. The resulting dependence of the switching field on the particle size and on the angle of the applied field is similar to what has been suggested by experimental evidence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342222
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