612 research outputs found
Exchange coupled perpendicular media
The potential of exchange spring bilayers and graded media is reviewed. An
analytical model for the optimization of graded media gives an optimal value of
the magnetic polarization of Js = 0.8 T. The optimum design allows for
thermally stable grains with grain diameters in the order of 3.3 nm, which
supports ultra high density up to 5 to 10 Tbit per inch2. The switching field
distribution is significantly reduced in bilayer media and graded media
compared to single phase media. For the graded media the switching field
distribution is reduced by about a factor of two. For bilayer media the minimum
switching field distribution is obtained for soft layer anisotropies about one
fifth of the hard layer anisotropy. The influence of precessional switching on
the reversal time and the reversal field is investigated in detail for magnetic
bilayers. Exchange spring bilayers can be reversed with field pulses of 20 ps.Comment: submitted to JMMM, 'Current Perspectives; Perpendicular recording
Calculation of coercivity of magnetic nanostructures at finite temperatures
We report a finite temperature micromagnetic method (FTM) that allows for the
calculation of the coercive field of arbitrary shaped magnetic nanostructures
at time scales of nanoseconds to years. Instead of directly solving the
Landau-Lifshitz-Gilbert equation, the coercive field is obtained without any
free parameter by solving a non linear equation, which arises from the
transition state theory. The method is applicable to magnetic structures where
coercivity is determined by one thermally activated reversal or nucleation
process. The method shows excellent agreement with experimentally obtained
coercive fields of magnetic nanostructures and provides a deeper understanding
of the mechanism of coercivity.Comment: submitted to Phys. Rev.
Mechanical oscillations of magnetic strips under the influence of external field
This is the final version of the article. Available from EDP Sciences via the DOI in this record.JEMS 2012 – Joint European Magnetic SymposiaBy application of a magnetic field on an amorphous metallic strip, the orientation of magnetization of Weiss domains can be changed. When the strip changes its length, this effect is called magnetostriction. We simulate this effect using a finite element method. In particular we calculate the change of the mechanical resonance frequency of a magnetic platelet as a function of the applied field. This gives a quantitative model of the influence of the applied magnetic field on the effective Young's Modulus of the material. © 2013 Owned by the authors, published by EDP Sciences
Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers
A vector spin model is used to show how frustrations within a multisublattice
antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting
on an exchange coupled ferromagnetic film. Possibilities for the existence of
exchange bias are examined and shown to exist for the case of weak chemical
disorder at the interface in an otherwise perfect structure. A sensitive
dependence on interlayer exchange is found for anisotropies acting on the
ferromagnet through the exchange coupling, and we show that a wide range of
anisotropies can appear even for a perfect crystalline structure with an
ideally flat interface.Comment: 7 pages, 7 figure
Multiscale modeling in micromagnetics : existence of solutions and numerical integration
Various applications ranging from spintronic devices, giant magnetoresistance sensors, and magnetic storage devices, include magnetic parts on very different length scales. Since the consideration of the Landau-Lifshitz-Gilbert equation (LLG) constrains the maximum element size to the exchange length within the media, it is numerically not attractive to simulate macroscopic parts with this approach. On the other hand, the magnetostatic Maxwell equations do not constrain the element size, but cannot describe the short-range exchange interaction accurately. A combination of both methods allows one to describe magnetic domains within the micromagnetic regime by use of LLG and also considers the macroscopic parts by a nonlinear material law using the Maxwell equations. In our work, we prove that under certain assumptions on the nonlinear material law, this multiscale version of LLG admits weak solutions. Our proof is constructive in the sense that we provide a linear-implicit numerical integrator for the multiscale model such that the numerically computable finite element solutions admit weak H1-convergence (at least for a subsequence) towards a weak solution
- …