• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.9
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• pp.546-550
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• 2017

Ferroelectric properties are governed by domain structures and domain wall motions, so it is of significance to understand domain evolution processes under mechanical stress. In the present study, in situ piezoresponse force microscopy (PFM) observation under compressive stress was carried out for a near-morphotropic PZT. Both $180^{\circ}$ and $non-180^{\circ}$ domain structures were observed from PFM images, and their habit planes were identified using electron backscatter diffraction in conjunction with PFM data. By externally applied mechanical stress, needle-like $non-180^{\circ}$ domain patterns were broadened via domain wall motions. This was interpreted via phenomenological approach such that the total energy minimization can be achieved by domain wall motion rather than domain nucleation mainly due to the local gradient energy. Meanwhile, no motion was observed from curvy $180^{\circ}$ domain walls under the mechanical stress, validating that $180^{\circ}$ domain walls are not directly influenced by mechanical stress.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.663-666
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• 1995

The domain wall motion coercivity, $H_{c}$, of magnetic materials arises from the dependence of the wall energy on localized changes in material parameters (magnetization, anisotropy, exchange energy densities). However, in an otherwise perfectly homogeneous material, the domain wall energy might change due to the change in the volume of the wall versus the wall position. Thus, any surface roughness contributes to the coercivity. Assuming different two-dimensional surface profiles, characterized by average wavelengths ${\lambda}_{x}$ and ${\lambda}_{y}$, and relative thickness variations dh/h, the coercivity due to the surface roughness has been calculated. Compared to the one dimensional case, the 2D coercivity is reduced. Depending on the ratio of ${\lambda}$ to the domain wall width, $H_{c}$ has a maximum around 2, and increasing with dh/h. With the decreasing thickness of the thin film and GMR heads, it might be the domain factor in determining the coercivity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.46-51
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• 2004

The cause for the variation of the initial permeability according to the Co substitution of Ni-Zn ferrite used in the LC resonance filter for the power line communication is studied. The initial permeability decreases as the quantity of Co diminishes, and the saturation magnetization increases as the quantity increases. Because the sintering density and the microstructure of ferrite show little change, the variation of the initial permeability can't be explained by the density, microstructure nor the saturation magnetization factor. The magnetocrystalline anisotropy increases, similar with the saturation magnetization, as the quantity of Co increases. The increase of magnetocrystalline anisotropy value makes the domain wall energy grow, which leads to the decrease of the initial permeability, because there's linear law between the magnetocrystalline anisotropy and the domain wall energy. The resonance frequency to Co substitution moved to high frequency band, due to the close relationship with domain wall energy, Initial permeability decreaed a little with an increase of Co contents, but resonace frequency moved to high frequency band. as a result of that, when Co was added 0.05 mol, initial permeability and resonace frequency was 75 and 25 MHz respectively.

• Proceedings of the Korean Magnestics Society Conference
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• 2014.05a
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• pp.120-121
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• 2014

We investigate the field-dependence of energy barrier for various cell diameters and two type of geometry through the NEB method. We find that the energy barrier can depend strongly on the cell size when the switching is governed by the domain wall motion. Moreover we also examine the cell size dependence of energy barrier for two type of cell geometry. In the presentation, we will discuss the effect of domain wall formation and more various cell size on the energy barrier in detail.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.372-375
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• 1995

The magnetization pattern of the central cross section deduced from the ac susceptibility measurement is described with an analytical function. The function is based on a charge-free configuration. The thickness of the $^{\circ}$ wall lying in a (100) plane and the wall energy are calculated analytically. Total energy of the domain structure has been minimized with Ritz's method. As the result of the minimization, the energy density of the $^{\circ}$ wall lying in a (100) plane is $0.58\;erg/cm^{2}$ and the one for a (110) plane is $1.18\;erg/cm^{2}$. Thicknesses of these walls are calculated numerically. Also, the calculation indicates there is a small central domain at the cross section without applied current. With the ac susceptibility measurement the existence of the domain without current can be identified.

• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.303-306
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• 2005

Effect of a ferromagnetic layer thickness on a narrow domain wall width is investigated. It is found that the narrow domain wall is formed in ferromagnetic/nonmagnetic/ferromagnetic multi layer structure with a loc at interlayer exchange coupling, and that the width of the narrow domain wall is affected by the ferromagnetic layer thickness. We performed micromagnetics simulations for the $Fe_1/Cr/Fe_2$ system with the local interlayer exchange coupling, with fixed thickness (20-nm) of $Fe_2$ layer and various $Fe_1$ layer thickness (1, 2, 4, and 6 nm). Consequently, we confirmed that the thinner the $Fe_1$ layer thickness, the thinner the width of the domain wall is formed, because of the surface energy nature of the interlayer exchange coupling.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1470-1474
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• 2004

This paper addresses the development of inverse compensation techniques for a class of ferromagnetic transducers including magnetostrictive actuators. In this work, hysteresis is modeled through the domain wall theory originally proposed by Jiles and Atherton[1]. This model is based on the quantification of the energy required to translate domain walls pinned at inclusions in the material with the magnetization at a given field level specified through the solution of an ordinary differential equation. A complementary differential equation is then employed to compute the inverse which can be used to compensate for hysteresis and nonlinear dynamics in control design.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.625-626
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• 2008

The magnetic domain-refining techniques such as ball scratching, laser irradiation and plasma have been developed to reduce the domain wall spacing and thus iron losses in Fe-3%Si grain-oriented silicon steels. In view point of magnetic properties, it was supposed that the locally residual stresses change the magnetoelastic energy of the material and thus the spacing between $180^{\circ}$ domain walls decreases in order to reduce the magnetostatic energy. The effect of laser irradiation on iron loss and magnetostriction reduction for Fe-3%Si grain-oriented steel were investigated. Since the local tensile stresses were induced at the surface of Fe-3%Si steel by the laser irradiation, the minimum iron loss caused by reducing eddy current loss was obtained in spiete of the decrease of permeability by hindering eddy current loss was obtained in spite of the decrease of permeability by hindering the domain wall movement around the induced stress field. Furthermore, the laser treated 3%Si steel has lower magnetostriction as compared to non laser-treated steel and is less sensitive to applying pre-stresses due to the volume reduction of $90^{\circ}$ domain in materials.

• Journal of the Korean Ceramic Society
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• v.23 no.4
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• pp.47-54
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• 1986

Since the wall mobility of bubble magnetic materials havin g the large q (q=Kac/2$\pi$$M_s^2$) like a $YFeO_3$ has been found to be proportional to the wall energy theoretically crystallographical direction dependence of wall energy calculated by the basis on the spin configuration of the bubble wall which lies in the ac plane was compared with the crystallographical direction dependence of wall mobility which was measured by the experiment. The sample was a single crystal of $YFeO_3$ which was cut into plate normal to the C axis and polished t a thickness of about 60${\mu}{\textrm}{m}$ The measurement of the wall mobility was carried out by optical system using the magneto-optic Faraday effect. From the good agreement of the crystallographical direction dependence of wall mobility and will energy it was found that the spin configuration of the bubble wall suggested is fair.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.240-243
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• 2005

A design procedure using spatial Fourier transform is presented for a structural-acoustic coupled radiator that can emit sound in the desired direction with high power and low side lobe level. The design procedure consists of three steps. Firstly, the structural-acoustic coupled radiator is chosen to obtain strong coupling between structural vibration and acoustic pressure. The radiator is composed by two spaces which are separated by a wall. Spaces can be categorized as reverberant finite space and unbounded semi-infinite space, and the wall are composed of two plates and an opening. The velocities on the wall are predicted. Secondly, directivity and energy distribution of radiator are predicted in wave number domain using spatial Fourier transform. Finally, optimal design variables are calculated using a dual optimal algorithm. Its computational example is presented including the directivity and resulting pressure distribution using proposed procedure.