• Journal of Magnetics
• /
• v.15 no.4
• /
• pp.169-172
• /
• 2010

The coercivity mechanism in permanent magnets was analyzed according to the effects of domain nucleation and domain wall pinning. The coercivity mechanism of a TbCo thin film with high perpendicular magnetic anisotropy was considered in terms of the local inhomogeneity in the thin film. The initial magnetization curves of the TbCo thin films demonstrated domain wall pinning to be the main contributor to the coercivity mechanism than domain nucleation. Based on the coercivity model proposed by Kronmuller et al., the inhomogeneity size acting as a domain wall pinning site was determined. Using the measured values of perpendicular anisotropy constant ($K_u$), saturation magnetization ($M_s$), and coercivity ($H_c$), the inhomogeneity size estimated in a TbCo thin film with high coercivity was approximately 9 nm.

• Geomechanics and Engineering
• /
• v.15 no.1
• /
• pp.645-657
• /
• 2018

The paper aims to analyze the behaviour of torsional type surface waves propagating through fluid saturated inhomogeneous porous media clamped between two inhomogeneous anisotropic media. We considered three types of inhomogeneities in upper anisotropic layer which varies exponentially, quadratically and hyperbolically with depth. The anisotropic half space inhomogeneity varies linearly with depth and intermediate layer is taken as inhomogeneous fluid saturated porous media with sinusoidal variation. Following Biot, the dispersion equation has been derived in a closed form which contains Whittaker's function and its derivative, for approximate result that have been expanded asymptotically up to second term. Possible particular cases have been established which are in perfect agreement with standard results and observe that when one of the upper layer vanishes and other layer is homogeneous isotropic over a homogeneous half space, the velocity of torsional type surface waves coincides with that of classical Love type wave. Comparative study has been made to identify the effects of various dimensionless parameters viz. inhomogeneity parameters, anisotropy parameters, porosity parameter, and initial stress parameters on the torsional wave propagation by means of graphs using MATLAB. The study has its own relevance in connection with the propagation of seismic waves in the earth where fluid saturated poroelastic layer is present.

• Proceedings of the Korean Magnestics Society Conference
• /
• 1992.10a
• /
• pp.32-33
• /
• 1992

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.6
• /
• pp.635-644
• /
• 2003

To ensure the reliability of ultrasonic nondestructive testing techniques for modern structural materials, the effects of anisotropy and inhomogeneity and the influence of non-planar component geometries on ultrasonic wave propagation have to be taken into account. In this article, fundamentals and applications of two analytical approaches to three-dimensional elastic beam field calculation are presented. Results for both isotropic materials including curved interfaces and for anisotropic media like composites are presented, covering field profiles for various types of transducers and the modeling of time-dependent rf-signals.

• Journal of the Korean Magnetics Society
• /
• v.7 no.4
• /
• pp.186-190
• /
• 1997

We measured an anisotropy inhomogeniety and dispersion of rf sputterd permalloy thin films by TBP(Transverse Biased Permeability) measurement method. Angular distribution function had a shape similar to the Lorentzian distribution, but magnitude distribution function deviates from the sysmetric Lorentzian distribution because of long tail to the region of a high Hk value. With increasing film thickness, the angular and magnitude anisotropy dispersion increased. The increase of angular dispersion was due to both the increase of grain size and local anisotropy in thicker films.

• Publications of The Korean Astronomical Society
• /
• v.7 no.1
• /
• pp.39-50
• /
• 1992

A velocity inhomogeneity, which is the regional preponderence of either radial or tangential orbits, is searched with the new technique proposed by Kim (1992) for Coma, Hydra I, and Abell 2256 cluster of galaxies. Conspicuous inhomogeneities are found in the Coma and A2256 which X-ray isophotes are indicative for their underlying potentials being ellipitcal in shape, Even in their central regions, zones that are dominated by radial orbits are clearly distinguishable from that of the tangential orbits, and defining the cluster 'equator' as the direction of maximum elongation of the X-ray isophotes, radial orbits dominate along this direction whereas tangential orbits dominate the 'polar' zones. Merger events that are evidenced in X-ray observations occur in the equatorial zones of Coma and A2256, suggesting preponderence of radial orbits in the zones, which is in good agreement with their velocity structures. On the other hand, the inhomogeneity in Hydra I turns out to be insignificant in the central regions and this is just what is expected from a cluster whose X-ray isophotes is nearly circular. The velocity distribution in regions further out, however, shows significant inhomogeneity and this seems to support the previous results that this cluster is likely to have substructures and velocity anisotropy.

• Journal of the Semiconductor & Display Technology
• /
• v.3 no.1
• /
• pp.31-34
• /
• 2004

We develop Mueller-matrix spectroscopic ellipsometry based on dual compensator configuration. This technique is very powerful for measuring surface anisotropy in nano-scale, especially when materials show depolarization. Dual-rotating compensator configuration is adopted with the rotational ratio of 5:3 originally developed by Collins et al[1]. The instrument can provide 250-point spectra over the wavelength range from 230 nm to 820 nm in one irradiance waveform with minimum acquisition time of Tc=10 s. In this work, the results obtained in transmission modes are presented for the initial attempt. We present calibration procedures to diagnose the system from the utilized data collected in transmission mode without sample. We expect that the instrument will have important applications in thin films and surfaces that have anisotropy and inhomogeneity.

• Journal of Magnetics
• /
• v.11 no.2
• /
• pp.70-73
• /
• 2006

The magnetization angle and thickness dependence of magnetic anisotropy in the exchange-biased [Pd/Co]${\times}$5/FeMn multilayers with an out-of-plane anisotropy were investigated to determine the origin of perpendicular exchange biasing. As the Co thickness increased to 1.5 nm in the [Pd(0.8 nm)/Co(t)]${\times}$5/FeMn(120 nm) films, the hysteresis loops were converted from square loops at a thin Co (<0.4 nm) to complicated round ones at a thick Co. The irregularly asymmetric step (IAS) at the left top of the loop appeared in the loop of the 0.6-nm Co film due to an inhomogeneity in the exchange anisotropy. As the Pd thickness increased to 1.6 nm, the step disappeared, and the perpendicular magnetic anisotropy was maximized in the Co thickness between 0.6 and 0.9 nm. The conversion of the magnetization loop along the magnetization angle coincided with the equation $H_{(eff)}=H_o\;cos{\theta}$. The IAS of the 0.8-nm Pd film disappeared after thermal annealing up to $200^{\circ}C$ under an external magnetic field.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
• /
• 2003.12a
• /
• pp.12-17
• /
• 2003

We develop Mueller-matrix spectroscopic ellipsometry based on dual compensator configuration. This technique is very powerful for measuring surface anisotropy in nano-scale, especially when materials show depolarization. Dual-rotating compensator configuration is adopted with the rotational ratio of 5:3 originally developed by Collins et al [1]. The instrument can provide 250-point spectra over the wavelength range from 230 nm to 820 nm in one irradiance waveform with minimum acquisition time of $Tc{\approx}10 s$. In this work, the results obtained in transmission modes are presented for the initial attempt. We present calibration procedures to diagnose the system from the utilize data collected in transmission mode without sample. We expect that the instrument will have important applications in thin films and surfaces that have anisotropy and inhomogeneity.

• Earthquakes and Structures
• /
• v.5 no.2
• /
• pp.161-205
• /
• 2013

We study seismically induced, anti-plane strain wave motion in a non-homogeneous geological region containing tunnels. Two different scenarios are considered: (a) The first models two tunnels in a finite geological region embedded within a laterally inhomogeneous, layered geological profile containing a seismic source. For this case, labelled as the first boundary-value problem (BVP 1), an efficient hybrid technique comprising the finite difference method (FDM) and the boundary element method (BEM) is developed and applied. Since the later method is based on the frequency-dependent fundamental solution of elastodynamics, the hybrid technique is defined in the frequency domain. Then, an inverse fast Fourier transformation (FFT) is used to recover time histories; (b) The second models a finite region with two tunnels, is embedded in a homogeneous half-plane, and is subjected to incident, time-harmonic SH-waves. This case, labelled as the second boundary-value problem (BVP 2), considers complex soil properties such as anisotropy, continuous inhomogeneity and poroelasticity. The computational approach is now the BEM alone, since solution of the surrounding half plane by the FDM is unnecessary. In sum, the hybrid FDM-BEM technique is able to quantify dependence of the signals that develop at the free surface to the following key parameters: seismic source properties and heterogeneous structure of the wave path (the FDM component) and near-surface geological deposits containing discontinuities in the form of tunnels (the BEM component). Finally, the hybrid technique is used for evaluating the seismic wave field that develops within a key geological cross-section of the Metro construction project in Thessaloniki, Greece, which includes the important Roman-era historical monument of Rotunda dating from the 3rd century A.D.