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A novel approach for solving the Landau-Lifshitz-Gilbert equation for antiferromagnets with the finite-element method is presented. The antiferromagnet is treated in a continuum theory which allows us to explore the domain structure on a mesoscopic length scale. The finite-element method is suitable to treat antiferromagnets with arbitrarily shaped grains as well as exchange coupled antiferromagnetic (AF)/ferromagnetic (F) structures. The change of the domain configuration in the antiferromagnet after the reversal of the ferromagnet leads to exchange bias in AF/F bilayers with perfectly compensated interfaces. Index Terms--Antiferromagnetic (AF) domain structure, antiferromagnets, exchange bias, finite-element method, micromagnetics.

Finite-element Langevin-dynamics simulations are performed in order to extract the attempt frequency of small magnetic particles as a function of an applied perpendicular field. The obtained values of the attempt frequency are in excellent agreement with the analytical results of [Kalmykov, J. Appl. Phys. 96, 1138 (2004)]. It is shown that an external field that is applied perpendicularly to the easy axis with a strength of just about 1% of the anisotropy field is strong enough that the framework of the transition state theory (TST) for broken symmetries can be applied. It is concluded that for most realistic structures, the attempt frequency can be numerically calculated by broken symmetry—TST formulism. [ABSTRACT FROM AUTHOR]

The Landau-Lifshitz-Gilbert equation and quasistatic Maxwell equations were solved simultaneously to calculate the read back signal of giant magnetoresistance read heads with a hybrid finite-element/boundary element method. The finite-element simulations show the influence of the sense current on the linearity of the reader, the effect of the exchange bias field on the sensor performance, and the influence of the Gilbert damping constant on the decay time of the read back voltage. All parts of the system, the layers of the giant magnetoresistance sensor, the hard bias magnets, the shields, and the recording layer are treated micromagnetically. In addition, the influence of the sense current onto the magnetization is taken into account self-consistently. The current distribution in the giant magnetoresistance stack is calculated from local resistivity which depends on the magnetization of the free and of the pinned layer. [ABSTRACT FROM AUTHOR]

A method for the calculation of the effective damping parameter as a function of particle size and electric conductivity is presented. An extended three-dimensional finite element/boundary element micromagnetic model is used to solve the Landau-Lifshitz-Gilbert equation together with the eddy current diffusion equation. From the change of energy with time an effective damping parameter is derived from which the net eddy current contribution is calculated. It is shown that the eddy current effects are reduced with an increasing applied field and are increased for materials with a low resistivity. Furthermore it is shown that the size of the particles, which designates the coherence of the spin structure, is essential for the eddy current net contribution. [ABSTRACT FROM AUTHOR]

The hysteresis properties of epitaxial SmCo/Co and SmCo/Fe bilayers are calculated by the solution of the Landau -- Lifshitz Gilbert equation. The thin film grain structure is taken into account using appropriate finite element techniques. The J(H) curve shows the typical exchange spring behavior for the bilayer if the soft magnetic layer thickness exceeds 10 nm. However, the reversible rotations of the magnetization for low external field deteriorate the maximum energy density product. Straight B(H) curves are obtained only for a Fe layer thickness of 5 nm. Magnetization reversal starts with the reversible rotation of the soft layer magnetization. Initially, the magnetization rotates in opposite directions in different regions of the film. The reversible rotations penetrate substantially into the hard layer. [ABSTRACT FROM AUTHOR]

Nanostructured granular Ni80Fe[sub 20] and Co films are studied using a 3D hybrid finite element/ boundary element model. Switching dynamics are calculated for external fields applied unidirectional after a rise time of 0.1 ns and for a 10 GHz rotational field with a field strength of H[sub ext] = 0.2 J[sub s]/µ[sub 0] (160 kA/m for NiFe and 280 kA/m for Co). The transient magnetization patterns show that reversal in the unidirectional field proceeds by the nucleation and propagation of end domains towards the center of the element. The switching time strongly depends on the Gilbert damping parameter α. Materials with uniaxial anisotropy (Co), require larger field, but exhibit shorter switching times. Reversal in rotational fields involves inhomogeneous rotation of the end domains towards the rotational field direction leading to partial flux-closure structures. Shorter switching times are obtained by the application of the 10 GHz rotational field (t[sub sw] = 0.05 ns). Precessional oscillation effects after abruptly switching off the external field which occurred in the NiFe square element, were suppressed in the granular Co film. Reducing the field to zero slowly inhibits the high frequency excitations in NiFe. [ABSTRACT FROM AUTHOR]

We have investigated domain wall pinning in Sm(Co,Fe,Cu,Zr)[sub z] based magnets with 3D micromagnetic simulations using a hybrid finite element/boundary element method. Transmission electron micrographs of magnets with Sm[sub 2] (Co,Fe) [sub 17] matrix and Sm(Co,Cu)[sub 5-7] precipitation phases were used to model the cellular microstructure. The pinning field was investigated for varying thickness of the intercellular phase. [ABSTRACT FROM AUTHOR]

Layer-selective writing of two layer bit patterned media is demonstrated by performing micromagnetic finite element simulations. Selectivity is achieved by controlling the frequency of an oscillating magnetic field in the gigahertz range, applied in addition to the head field. Generation of the microwave field by means of a wire next to the tip of a single pole head is proposed. The Oersted field from the alternating current induces magnetic oscillations in the pole tip which create a high frequency field that is superimposed to the perpendicular write field. The amplitude of the ac field component is in the order of 0.1 T. [ABSTRACT FROM AUTHOR]

A novel type of exchange spring media is proposed for magnetic recording systems consisting of a hard/soft bilayer. Finite element micromagnetic simulations show that the reversal modes induced by the external write field are significantly different from the thermally activated switching processes. Thus, the bilayers can be optimized in order to achieve a high thermal stability without increase of coercive field. In grains with identical size and coercivity an optimized bilayer reaches an energy barrier exceeding those of optimized single phase media by more than a factor of two. Additionally the lower angular dependence of coercivity of exchange spring media will improve the signal to noise ratio. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the transient magnetization states during switching in granular nanoelements using finite element simulation. Features of the micromagnetic model; Influence of magnetocrystalline anisotropy on the switching behavior of thin cobalt and permalloy film elements; Determination of the time of evolution of the polarization.

Presents a study which conducted a finite element simulation of discrete magnetic media with granular structure. Comparison of the magnetization reversal process in perpendicular granular films, patterned media and a single magnetic island; Micromagnetics; Experimental results.

In this article we describe the thermal relaxation in anti-ferromagnetic/ferromagnetic bilayers using a hybrid method that combines a kinetic Monte Carlo technique with magnetization dynamics following the Landau Lifshitz Gilbert equation. A granular anti-ferromagnetic layer is exchange coupled to an amorphous ferromagnetic layer and discretized using a finite element method. Calculations are made to help clarify how the underlying magnetic structure is related to the measured exchange bias fields as a function of temperature for the case of amorphous Co65.5Fe14.5B20/granular Ir22Mn78 bilayers. Our calculations are in excellent agreement with experimentally measured macro-magnetic properties of these bilayers. [ABSTRACT FROM AUTHOR]

Minimum energy paths and energy barriers are calculated for complex micromagnetic systems. The method is based on the nudged elastic band method and uses finite-element techniques to represent granular structures. The method was found to be robust and fast for both simple test problems as well as for large systems such as patterned granular media. The method is used to estimate the energy barriers in CoCr-based perpendicular recording media. [Copyright &y& Elsevier]

We have investigated the magnetic properties of submicron soft magnetic cylindrical nanodots using an analytical model as well as three dimensional numerical finite element simulations. A detailed comparison of the magnetic vortex state shows the differences between these two models. It appears that the magnetic surface charges play a crucial role in the equilibrium magnetization distribution especially for shifted vortices. Finally, the magnetic phase diagram for soft magnetic particles with varying aspect ratio is presented. [Copyright &y& Elsevier]

Langevin micromagnetics treats finite temperature effects by adding a thermal fluctuation field, Hth, to the effective field. If combined with the finite element method a large system of stochastic differential equations (SDEs) has to be solved. In this paper, a new semi-implicit method is used to treat the system of SDEs on magnetic sensor elements. Fluctuations are of immense importance in recording industry because they lead to instabilities and also increase the noise. The results show that according to the model conclusions the fluctuations of the magnetization increase slightly with the temperature. [Copyright &y& Elsevier]

Abstract: We perform a qualitative analysis of phase locking in a double point-contact spin–valve system by solving the Landau–Lifshitz–Gilbert–Slonzewski equation using a hybrid-finite-element method. We show that the phase-locking behaviour depends on the applied field angle. Starting from a low field angle, the locking-current difference between the current through contact A and B increases with increasing angle up to a maximum of 14mA at 30°, and it decreases thereafter until it reaches a minimum of 1mA at 75°. The tunability of the phase-lock frequency with current decreases linearly with increasing out-of-plane angle from 45 to 21MHz/mA. [Copyright &y& Elsevier]