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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Influence of domain wall structure on pinning characteristics with self-induced anisotropy

H. Asada, Y. Wasada, J. Yamasaki, M. Takezawa, and T. Koyanagi

J. Appl. Phys. 93, 7447 (2003); http://dx.doi.org/10.1063/1.1560703 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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Wall pinning effects with self-induced spatially varying uniaxial anisotropy in various thick films have been studied using micromagnetic simulation based on the Landau–Lifshitz–Gilbert equation. In the simulation, the discretization region is in the cross section normal to the film plane. It is clarified that the wall structure is strongly related to pinning characteristics. Depinning fields of the wall having a flux-closure asymmetric vortex (C-shaped wall) are different in the wall movement directions due to the asymmetric wall structure. On the other hand, depinning fields of the wall with two vortices (S-shaped wall) which have a symmetric structure do not depend on the wall movement direction. Depinning fields for the S-shaped wall are different from both depinning fields for the C-shaped wall. © 2003 American Institute of Physics.
Show PACS
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Transport modeling of Py film with antidot array

J. Guo and M. B. A. Jalil

J. Appl. Phys. 93, 7450 (2003); http://dx.doi.org/10.1063/1.1557364 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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We present a model to investigate the lateral transport and anisotropic magnetoresistance (AMR) of a permalloy film, with a two-dimensional array of unfilled holes (antidots). The current density distribution j is first obtained numerically by solving the Poisson equation in the absence of B field, while the magnetization M of the film is calculated via micromagnetics. The M and j distributions are linearly interpolated through the sample, and then combined in a self-consistent scheme to obtain the galvanomagnetic effects (normal and planar Hall effects), which affect the current direction. The overall AMR is evaluated from the parallel contributions of the resulting current paths. Modifying the film geometry by reducing the antidot spacing results in an increase in the peak AMR ratio, which may be explained by the inhomogeneous current density and magnetization alignment induced by the antidots. © 2003 American Institute of Physics.
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75.47.Np Metals and alloys
75.30.Gw Magnetic anisotropy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.At Metal and metallic alloys

Modeling a perpendicular recording medium using a variational method

P. H. W. Ridley, A. W. Spargo, G. V. Hines, and G. W. Roberts

J. Appl. Phys. 93, 7453 (2003); http://dx.doi.org/10.1063/1.1557363 (3 pages)

Online Publication Date: 9 May 2003

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A micromagnetic model is used to investigate the dynamic behavior of a perpendicular recording medium which consists of a hard data layer and a soft underlayer. A variational finite element form of the Gilbert equation of motion is used to simulate the magnetization dynamics without thermal fluctuations. A computationally efficient variational approximation is used for the magnetization dynamics. The demagnetizing field calculation uses a hybrid finite element/boundary element calculation or a hybrid wavelet/boundary element method. The variational scheme is particularly suited to reducing numerical errors in areas of the material where magnetic inhomogeneities occur such as in the data layer during the nucleation of domains. Perpendicular recording media presents a viable alternative to the conventional longitudinal type in extending the superparamagnetic limit. Higher field strengths allowing higher densities have been shown to be sensitive to the characteristics of the soft underlayer. The dynamic effects of the soft underlayer are investigated for thicknesses between 65 and 80 nm. Interaction effects between the data layer and soft underlayer are observed to be more prominent in the 65 nm thickness. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
02.30.Xx Calculus of variations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
02.70.Dh Finite-element and Galerkin methods
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Micromagnetic study of nonlinear effects in soft magnetic materials

G. Mohler, A. W. Harter, and R. L. Moore

J. Appl. Phys. 93, 7456 (2003); http://dx.doi.org/10.1063/1.1557362 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Numerical simulation is used to study the linear and nonlinear effects of increasing incident power density on soft magnetic materials at the microscale. A magnetic field pulse with Gaussian time dependence and variable strength is numerically applied to a magnetic particulate in an equilibrium state. The field-dependent dynamic susceptibility (M/H) is calculated from the Fourier transform of the magnetization response. Calculations show that as the magnitude of the excitation field exceeds a critical value, the system becomes nonlinear. At this point, the ferromagnetic resonance should become suppressed and span a wider range of frequencies. Two systems are simulated in the linear and nonlinear regimes; one system shows complete agreement with established nonlinear theory, while the other shows unusual behavior. Both systems agree with linear theory at low fields, and vanishing susceptibility at excessively high fields is observed for both. © 2003 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Design of high-magnetic field gradient sources for controlling magnetically induced flow of ferrofluids in microfluidic systems

W. He, S. J. Lee, D. C. Jiles, D. H. Schmidt, M. D. Porter, and R. Shinar

J. Appl. Phys. 93, 7459 (2003); http://dx.doi.org/10.1063/1.1557361 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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The use of miniature electromagnets for ferrofluid-actuated liquid dispensing into microfluidic channels has been investigated by numerical simulations using the finite element method and measurements of fluid displacement and flow rate. The simulations illustrate the effect of structural and geometrical parameters of single and paired solenoid coils on the magnetic force experienced by the ferrofluid. Dual solenoids were used for extended fluid displacement. Ferrofluid positioning and flow rates were controlled also by using a solenoid with an iron core. The experimental measurements of fluid flow in capillaries were used to validate the modeling calculations. The results can be used as a basis for the development of on-chip ferrofluid-based devices integrated with microfluidic architectures. © 2003 American Institute of Physics.
Show PACS
75.50.Mm Magnetic liquids
47.85.L- Flow control
47.85.Np Fluidics
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.65.-d Magnetohydrodynamics and electrohydrodynamics
82.70.Kj Emulsions and suspensions
82.70.Dd Colloids
47.55.Kf Particle-laden flows
47.11.-j Computational methods in fluid dynamics
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