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  • 1
    Electronic Resource
    Electronic Resource
    Equilibrium analysis of magnetization reversal in cobalt and permalloy platelets (abstract) : 37th annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6529-6529 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The local equations of stable equilibrium for the magnetization distribution in a ferromagnetic system in the micromagnetic approximation are derived from the Gibbs free energy, by application of the principle of minimum total potential. The resulting boundary value problem consists of a system of second order integrodifferential equations and boundary conditions for the magnetization distribution. These are solved iteratively using a finite-difference method and applied to the study of thin regularly shaped cobalt particles of sub and supra micron sizes with various aspect ratios and exchange coupling strengths. Permalloy platelets are also studied for size and aspect ratio dependence. Magnetization curves and distributions are calculated and the effect of aspect ratio and exchange coupling on the distributions are deduced. Comparison with previous calculations using finite element techniques1,2 are made. Variational methods using Hamilton's principle suggest that a dynamic extension can be developed3,4 to model the transient processes associated with the irreversible phases of the magnetization reversal. Such a model based on equations of motion in the Hamiltonian form is currently being developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352604
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic viscosity in perpendicular media (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4431-4438 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The remanent magnetization of fine particle media of perpendicular anisotropy is known to exhibit a time decay of pseudologarithmic form. The viscous properties are to a large extent determined by the magnetostatic particle interaction and the particle size. A mean-field model of a perfectly aligned ensemble of Stoner–Wohlfarth particles is presented that gives a qualitative description of the hysteretic and time-dependent properties of particulate perpendicular media. The time decay of the remanent magnetization of Alumite media after initial magnetic saturation was measured. The decay was found to be logarithmic within the measuring period, and a coefficient of magnetic viscosity was obtained. Although the reversal mechanism for the particles in Alumite media is known to be incoherent, a good qualitative agreement between the theoretical model and the measurements was found by introducing a reduced effective volume acting as a scaling factor that accounts for the discrepancy in reversal mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349127
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  • 3
    Electronic Resource
    Electronic Resource
    A magnetic evaluation of interaction and noise characteristics of CoNiCr thin films : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4733-4735 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nature of media recording noise in metallic, quasiparticulate thin films is principally related to the grain size, crystallographic orientation, and intergranular exchange and magnetostatic coupling in the films. In this study the results of a magnetic evaluation of magnetostatic interactions in CoNiCr thin films of varying Cr underlayer thickness are reported. The evaluation is undertaken through the measurement and comparison of remanence curves. The results presented here indicate enhanced cooperative switching as Cr underlayer thickness is reduced from 2000 to 100 A(ring), with a strong correlation between signal-to-noise measurements. In addition, the transition from principally exchange-coupled to quasiparticulate thin films, as Cr underlayer thickness increases, has been established.〈lz〉 〈lz〉 〈lz〉 〈lz〉 〈lz〉 〈lz〉
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348263
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal fluctuations in a pair of magnetostatically coupled particles : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6501-6503 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of the thermal agitation on the switching dynamics for a pair of identical uniaxially anisotropic dipoles is studied for the case of the applied field parallel to the bond direction and the common anisotropy axis. A set of Langevin equations was derived from the micromagnetic energy expression and solved numerically. The switching behavior resembles a random walk over the energy barrier arising from the anisotropy of the system. The relaxation time is computed as a function of temperature, applied field, and coupling strength. The temperature dependence of the maximum energy of the fluctuations provides a method of evaluating the energy barrier of reversal. The thermal agitation is shown to reduce the symmetry of the "fanning'' reversal mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352594
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  • 5
    Electronic Resource
    Electronic Resource
    Reptation effects in particulate systems. I. Theoretical predictions : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6653-6655 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we derive a theory which describes the effects of field cycles on the magnetization in particulate systems, i.e., the reptation effects. This theory predicts that the difference between reptation and time-dependence measurements arises from time dependence which occurs during the cycling of the magnetic field, i.e., during the field sweep. These predictions are found to be in good agreement with experimental data published in the following article [Lewis et al. (these proceedings)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352545
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  • 6
    Electronic Resource
    Electronic Resource
    Ferromagnetic resonance and transverse susceptibility measurements on particulate recording media (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6738-6738 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The FMR absorption of different particulate recording tapes was investigated at microwave frequencies in the X band and Q band using temperatures from 70 to 400 K. The FMR spectra as a function of the external magnetic field were recorded for four different orientations of the static and high frequency magnetic fields with respect to the tape. Particular interest of the experimental and theoretical study was devoted to the interaction fields between the particles, texture effects within the tape sample and the effective anisotropy fields. Tape samples with different particle materials, varying packing densities and orientation ratios were prepared. The shape and line position of the FMR spectra obtained are strongly dependent on the pigment material and the tape parameters mentioned above. The experimental data are compared with theoretical calculations, based on a phenomenological model and a computer simulation. This comparison gives information on the orientational distribution of the particles, which is the most important source for inhomogeneous line broadening, the mean interaction, and anisotropy fields which govern the line position, the effective magnetization of the tape, and the relaxation time. The influence of the crystalline anisotropy can be investigated via temperature dependent measurements. The results are proved by additional transverse susceptibility measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352520
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  • 7
    Electronic Resource
    Electronic Resource
    The temperature relationship of the fluctuation field and coercivity in NdFeB alloys : 35TH ANNUAL CONFERENCE ON MAGENTISM AND MAGNETIC MATERIALS San Diego, California (USA) 29 Oct−1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5495-5497 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coercivity Hc and fluctuation field Hf are intrinsic properties of any magnetic system exhibiting hysteresis. They are measures of the energy barriers resisting magnetization reversal and may be used to probe the nature of the magnetization processes. The variation of coercivity as a function of temperature and of the fluctuation field as a function of field and temperature have been studied for sintered and melt-spun NdFeB. The fluctuation field has been found to vary with field in the sintered material indicating that interactions play an important role in the nucleation of reverse domains while it remained constant in the melt-spun sample. The relationship between the coercivity and fluctuation field has been studied and found to be consistent with the Barbier plot though some deviation from the expected curve was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347978
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  • 8
    Electronic Resource
    Electronic Resource
    The mathematical modeling of the acquisition of gyroremanent magnetization in a single domain particle (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4481-4483 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The origins of gyroremanent magnetization (GRM) in single domain particles are studied using a dynamic model based on the Landau–Lifschitz equation. The results show an asymmetry in the motion of the magnetic moment of a particle with three unequal axes of anisotropy. This asymmetry is interpreted in terms of an effective bias field which gives a good qualitative explanation of the origins of GRM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344888
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical studies of the field-cooled and zero-field cooled magnetization of interacting fine particles (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4340-4342 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have applied a Monte–Carlo model of the properties of an interacting fine particle system to calculations of the field-cooled (FC) and zero-field cooled (ZFC) magnetization. The variation of Tg, the temperature peak, in the ZFC is also calculated. For an interacting system the effective energy barrier distribution is dependent on the packing density, and this is reflected in the Tg vs H curve. An important result is the demonstration that magnetostatic interactions between the particles can give rise to a peak in the FC magnetization. This is in agreement with experiments and is a result of the magnetic order introduced by the magnetostatic interactions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370361
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  • 10
    Electronic Resource
    Electronic Resource
    Simulations of fast switching in exchange coupled longitudinal thin-film media (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5012-5014 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a Langevin dynamic simulation of high speed switching in longitudinal thin-film media. The model assumes a randomly placed set of grains with a particle size distribution which interact via magnetostatic and exchange fields. The dynamic properties of the material are simulated using the Langevin dynamic formalism which is essentially the Landau–Lifshitz–Gilbert equation of motion augmented by a random field whose properties are determined by the fluctuation–dissipation theorem. We have simulated pulsed-field magnetization and remanence curves which are obtained by applying a field pulse to a system in the remanent magnetization state. Calculations of the time dependence of the magnetization, and the time dependence of the coercivity have been made. The high frequency dynamic behavior of the systems is found to be strongly dependent on the value of the exchange coupling between the grains. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370075
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