In previous works, we have obtained
several results on the numerical
analysis of magnetostrictive materials
at microscopic scale. These studies,
based on the minimization of the total
energy functional of the system,
include the existence and the
approximation of solutions and the
associated numerical experiments on
two-dimensional samples.
Next, we have considered the numerical
analysis of two-dimensional cubic
crystals of ferromagnetic materials
with emphasis on the thickness of
the walls and their evolution under
an incremental magnetic field and
the effect of nonmagnetic inclusions.
This contribution discusses more
specifically two extensions
i) to three dimensional ferromagnetic
materials (computation and
representation of magnetic domains
and Bloch walls) and
ii) to the case of two-dimensional
polycrystals, in particular, the
magnetic domains for adjacent
rectangular crystals whose easy lines
of magnetization have different
orientations.
A ferromagnetic material located into a unidirectional exterior magnetic field vector Hext takes a new internal magnetization which induces closure domains separated by walls. When the magnetic field vector Hext varies from a saturated value Hmax vector ex to -Hmax vector ex, we can observe hysterisis phenomenon and motion of the walls. The numerical approximation of these phenomena is difficult since the associated modelization is nonlinear and the magnetization field vector m has to satisfy vector m equals constant. The associate modelization, an efficient minimization algorithm (augmented Lagrangian method) and corresponding results have been presented in the last SPIE meeting. This contribution discusses the coupling between magnetic effects and elastic effects which can be met in magnetostrictive materials.
In this paper, we report some results obtained in computational micromagnetism, particularly the numerical approximation of hysteresis phenomenon and the numerical approximation of closure domains. We successively consider a brief recall about micromagnetism, a mathematical modelization of a ferromagnetic material by using the total energy functional of the system, a choice of an appropriate functional space and an associated existence theorem, a convenient minimization algorithm based on an augmented Lagrangian method used in combination with an appropriated finite element method. These developments are illustrated upon the study of a piece of a very thin rectangular plate of a ferromagnetic material located in a coplanar unidirectional exterior magnetic field Hest. Under the action of Hest, we compute the internal magnetization of the plate and then, by decreasing step by step the external field from Hmaxex to -Hmaxex, we find back numerically two physical phenomena, the hysterisis and the motion of walls of the closure domains.
A new surface pretreating method of the LPE HgCdTe surface involves three steps. The state of the surface before and after the pre-treatment process has been investigated by Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy. The treated surface following the processes is compared to the untreated surface. The results show the Electron Channel Pattern and morphology of the treated surface are better than that of the untreated surface. The optical and electrical parameters of before and after the treated epilayers have not changed. The oxides and contaminants have been reduced and eliminated. The photodiode arrays with good performance have been fabricated on the LPE HgCdTe which is treated as the described approach. The experimental results indicate that the appropriate surface pre-treatment is an important part of the photodiode array technology.
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