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Reversal modes and energy barriers in patterned media

by Rok Dittrich

The nudged elastic band method is applied to calculate energy barriers and minimum energy paths for the thermal reversal of patterned recording media. Shown is a perpendicular patterned media with 70 nm island size. The finite element method allows the modelling of complex geometries. The effect of intergrain exchange coupling strength can thus be investigated. Below a critical coupling strength the magnetization reversal process changes from single large island reversal to the individual switching of separated grains. The colour code corresponds to the out of plane component of the magnetization.

Patterned

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Vortex core reversal by Bloch points

by Rok Dittrich

Minimum energy paths for the thermal reversal of the vortex core in a softmagnetic disk are calculated. The vortex core reverses by the nucleation and displacement of a Bloch point singularity. Shown is a cut across the thickness of the finite element mesh (Permalloy disk, 100 nm radius, 50 nm thickness). The colour code corresponds to the z-component of the magnetization. The magnetization state has a Bloch point in the center of the disk.

Bloch_Point

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Thermally induced magnetization reversal in AFC media

by Rok Dittrich

AFC media is a prominent candidate where thermal stability is increased by a stabilizing layer. The figure shows a finite element model of 25 AFC grains. The recording layer and the stabilizing layer are separated by a thin nonmagnetic Ru-spacer of about 0.8 nm thickness which couples the two layers antiferromagnetically.

The thermal stability of the recording material is determined by the relevant energy barriers which are calculated using the nudged elastic band method.

afcmodel

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Energy barriers in magnetic random access memory elements

by Rok Dittrich

Minimum energy paths and energy barriers are calculated for the free data layer in elliptical magnetic random access memory elements using the nudged elastic band method. The reversal mode in the minimum energy path depends on the strength of the external field.

The figure shows an array of MRAM cells with current lines. To switch the center cell a current is applied in the two red colored current lines. The resulting field (red arrow) is strong enough to switch the magnetization. Half selected cells feel a weaker field (blue arrows) either parallel or perpendicular to the easy axis.

mram_model

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Domain wall velocity in Co-nanowires

by Hermann Forster

The velocity of a domain wall during the motion through a Co-nanowire was calculated. The velocity depends on the domain wall structure.

domain wall structures

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Adaptive mesh refinement

by Hermann Forster

The development of an adaptive mesh refinement algorithm helps to bridge the lengthscales used in micromagnetic simulations. The finite elemente mesh is dynamically adapted to the current magnetization distribution.

refined mesh

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Granular Co-nanowires

by Hermann Forster

The switching process of interacting granular Co nanowires is investigated. The numerical results show that finite element micromagnetics can explain the influence of the microstructure in magnetic nano-systems.

granular Co-nanowire

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Exchange bias in F/AF systems with perfectly compensated interfaces

by Markus Kirschner

The interacting grain model assumes perfectly compensated interfaces between the granular ferro- and antiferromagnet and gives bias fields and coercivities comparable to those observed experimentally. The behavior of the hysteresis shift and the coercivity for varying material parameters is investigated.

Exchange bias

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Intergranular exchange in perpendicular recording media

by Martin P. Stehno

The process of switching a bit was investigated in a simple model system. The bit switching times were determined as a function of intergranular exchange. Different reversal characteristics were found varying parameters such as field rise time, easy-axis distribution in the grains, or grain shape distribution.

Intergrain

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Sept. 2004