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15 May 2002

Volume 91, Issue 10, pp. 6227-8917

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Magnetic domain wall transitions based on chirality change and vortex position in thin Permalloy™ films

M. Redjdal, A. Kákay, M. F. Ruane, and F. B. Humphrey

J. Appl. Phys. 91, 8278 (2002); http://dx.doi.org/10.1063/1.1454983 (3 pages) | Cited 3 times

Online Publication Date: 13 May 2002

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The three possible transitions of a wall involving a change of chirality and position of a vortex were previously identified in Permalloy™ using the Kerr effect. These transitions have now been simulated using direct integration of the Landau–Lifshitz–Gilbert equation in a 1 300 000 point Cartesian lattice. One transition is between two C-shaped, same chirality walls whose vortices are on opposite sides. The transition is done via a 32-nm-long pi-VBL structure at the surfaces and at the center via a shape transition 117 nm long. The pi-vertical Bloch line (pi-VBL), which changes chirality along the wall, conducts the flux between the walls of opposite chirality via a vortex structure by letting the magnetization rotate out of the plane of the walls at the center of this vortex. The Néel caps switch chirality via an antivortex flux at one surface and a vortex flux at the other surface. Another transition is a pi-VBL that takes place between two C-shaped, opposite chirality walls whose vortices are on opposite sides of the walls. The transition between the Néel caps of same chirality is a jog at the top surface, while it is a vortex–antivortex pair at the bottom surface. © 2002 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Micromagnetic simulations of antiferromagnetically coupled media

S. J. Greaves, K. K. Tham, M. Miura, and A. M. Goodman

J. Appl. Phys. 91, 8281 (2002); http://dx.doi.org/10.1063/1.1447534 (3 pages) | Cited 2 times

Online Publication Date: 13 May 2002

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Antiferromagnetically coupled media were simulated using a micromagnetic model. Magnetic parameters, initially determined by fitting hysteresis loops to experimental media, were varied to determine their effect upon recording performance. The signal-to-noise ratio can be enhanced by tailoring the magnetic properties of the bias layer to an optimum Ms, introducing a small amount of exchange coupling and orienting the media. © 2002 American Institute of Physics.
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75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.30.Gw Magnetic anisotropy

Simulation of magnetic recording in media with irregular microstructures

S. J. Greaves, M. Miura, and A. M. Goodman

J. Appl. Phys. 91, 8284 (2002); http://dx.doi.org/10.1063/1.1447535 (3 pages)

Online Publication Date: 13 May 2002

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A realistic simulation of a magnetic recording medium necessitates the use of a realistic grain microstructure. However, the calculation of the demagnetizing field for irregular structures is difficult. In this article an approach to the calculation of demagnetizing tensors is described which allows for the use of arbitrary microstructures and also allows nonmagnetic grain boundaries to be included in the model. Simulations of media with various grain size distributions are described. A narrower distribution of grain sizes results in higher signal-to-noise ratios for recorded tracks and increased resistance to stray fields. © 2002 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials
61.72.Mm Grain and twin boundaries

Micromagnetic modeling of overlaid exchange-biased giant magnetoresistance head

Yuankai Zheng, Dan You, and Yihong Wu

J. Appl. Phys. 91, 8287 (2002); http://dx.doi.org/10.1063/1.1447184 (3 pages)

Online Publication Date: 13 May 2002

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Overlaid exchange-biased structures for giant magnetoresistance head have been proposed and investigated. A home-developed three-dimensional micromagnetic modeling tool has been used to simulate synthetic antiferromagnetic spin valves of this type of biased structure with dimensions of 100 nm in width and 80 nm in height. Simulation results showed that, with a properly chosen antiferromagnetic material and structure, the exchange-biasing field could be made sufficient to suppress the noise without severely reducing the sensitivity. The sensitivity of overlaid exchange-biased spin valves is 1.73 times that of the abutted hard biased ones. Microtrack profiles showed that side reading effect could be suppressed effectively with an effective exchange-biasing field over 600 Oe. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ss Magnetic recording materials
75.30.Et Exchange and superexchange interactions

Efficient three-dimensional numerical magnetic shield model

John Oti

J. Appl. Phys. 91, 8290 (2002); http://dx.doi.org/10.1063/1.1456417 (3 pages)

Online Publication Date: 13 May 2002

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We describe an accurate, flexible, and efficient three-dimensional magnetic shield model that is suitable for use within generic micromagnetic models. The model accounts for both shield saturation effects (to first order) and fringing field edge effects due to the finite size of the shields. The model is described for shields with shapes in the form of rectangular segments; however, it is equally applicable to other shield shapes. In this method, each shield object is treated as a field source owing to “magnetic charge” distributions that are induced on its bounding surfaces. The charge distributions are obtained from image boundary conditions imposed on the total local fields acting at numerical mesh points defined for the shield surfaces. A numerical relaxation procedure is applied to ensure self-consistent charge distributions. We compare this approach with traditional magnetic image models, discuss its properties and demonstrate its application in calculating the distortion of the interaction field between a soft recording head and magnetic transitions in recording media. © 2002 American Institute of Physics.
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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
07.55.Nk Magnetic shielding in instruments
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ss Magnetic recording materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetization reversal of elliptical Co/Cu/Co pseudo-spin valve dots

N. Dao, S. L. Whittenburg, Y. Hao, C. A. Ross, L. M. Malkinski, and J. Q. Wang

J. Appl. Phys. 91, 8293 (2002); http://dx.doi.org/10.1063/1.1454984 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2002

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We present our recent simulated results on Cr (5 nm)/ Cu (5 nm)/ Co (5 nm)/ Cu (3 nm)/ Co (2 nm) pseudo-spin valve dots. The simulated results agree qualitatively with the experimental results. Three different sizes of elliptical dots, 150 nm×105 nm, 175 nm×70 nm, and 200 nm×60 nm, were simulated. Our simulations show that in these types of dots magnetization reversal occurs by the formation of domain walls: 90° for 175 nm×70 nm and 360° for 200 nm×60 nm. No domain wall was observed in the reversal of the 150 nm×105 nm dots. For such dots, the simulated loops show a small two-step reversal pattern with the thin upper layer partially reversing followed by complete reversal of both layers at higher fields. In the larger dots, a two-step reversal is clearly observed both in the simulation and experiment. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.60.Jk Magnetization reversal mechanisms
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.40.Mg Numerical simulation studies

Micromagnetic simulation for tunnel junctions with synthetic antiferromagnetic pinned layers annealed at different external fields

Yaowen Liu, Zongzhi Zhang, Zhengang Zhang, P. P. Freitas, and J. L. Martins

J. Appl. Phys. 91, 8296 (2002); http://dx.doi.org/10.1063/1.1447484 (3 pages) | Cited 13 times

Online Publication Date: 13 May 2002

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Bottom-pinned tunnel junctions with synthetic antiferromagnetic (SAF) pinned layers require an annealing step near the blocking temperature under an applied magnetic field to set the exchange direction. Experimental results (anneal at 270 °C, for a MnIr/SAF structure) show that the tunnel magnetoresistance signal is strongly reduced (3%) for anneals under an applied field of 2000 Oe, when compared with large tunnel magnetoresistance signals (>20%) obtained for samples annealed either at low (250 Oe) or high (5000 Oe) fields. To clearly understand this behavior, a micromagnetic simulation was performed to demonstrate the magnetization evolution of the SAF layer during the different field anneals. The simulated magnetization configurations indicate that the SAF layer net moment aligns parallel to the applied field (high field anneal) or antiparallel to the applied field (low field anneal), leading in both cases to high TMR signal. After annealing at intermediate field, the SAF net moment rotates almost orthogonal to the annealing field direction, resulting in the measured low TMR signal. © 2002 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.50.Ee Antiferromagnetics
75.40.Mg Numerical simulation studies
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