• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.387-390
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• 1995

We have developed a new method for measuring the M-H hysteresis loop of a spheroid-shape magnetic material having a uniaxial anisotropy and discussed its accuracy at fields near the coercivity. Our torque magnetometric method simultaneously gives the saturation magnetization and the remnant magnetization. Furthermore, the coercivity depending on the applied field orientation is accurately measured by this simple technique. An accuracy of the present method is negligibly affected even at fields near the coercivity, where the magnetization is not uniform. The technique makes a torque magnetometer an extremely high sensitive tool for measuring M-H hysteresis loop.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.115-118
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• 2016

We investigated the magnetocrystalline anisotropy of pure ${\alpha}^{{\prime}{\prime}}-Fe_{16}N_2$ by using full-potential linearized augmented plane wave method (FLAPW). A very high magnetic moment was obtained for Fe (4d) site due to the lattice expansion in the z-direction, while the magnetic moment of Fe (4e) and (8h) site were suppressed due to hybridization with neighboring N atom. The calculated spin magnetic moments for different Fe sites (4d, 4e and 8h) were in good agreement with previously reported values. Due to the tetragonal distortion, we found a very large uniaxial anisotropy constant of $0.58MJ/m^3$. Besides, a high value of magnetization of 1.76MA/m was obtained. In additon, the estimated coercive field and maximum energy product of 6.51 kOe and 71.7 MGOe were obtained for pure ${\alpha}^{{\prime}{\prime}}-Fe_{16}N_2$. This may suggest that the ${\alpha}^{{\prime}{\prime}}-Fe_{16}N_2$ can be utilized for potential rare-earth free permanent magnet material.

• Journal of the Korean Geophysical Society
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• v.3 no.2
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• pp.99-112
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• 2000

The Iksan Jurassic Granite shows relatively less fractures and homogeneous rock fabrics, and is one of the most popular stone materials for architectures and sculptures. Almost mutually perpendicular rift, grain, and halfway in the Iksan Jurassic Granite are well known to quarrymen based on its splitting directions, and therefore it should exhibit orthorhombic symmetry. Theoretically, there are 9 independent elastic stiffness coefficients $(C_{1111},\;C_{2222},\;C_{3333},\;C_{2323},\;C_{1313},\;C_{1212},\;C_{1122},\;C_{2233},\;and\;C_{1133})$ for orthorhombic anisotropy. In order to characterize the static and dynamic elastic properties of the Iksan Jurassic Granite, triaxial strains under uniaxial compressive stresses and ultrasonic velocities of elastic waves in three different polarizations are measured. Both experiments are carried out with six directional core samples from massive rock body. Using the results of experiments and the densities measured independently, the static and dynamic elastic coefficients are computed by simple mathematical manipulation derived from the governing equations for general anisotropic media. The static elastic coefficients increase ar uniaxial compressive stress rises. Among those, the static elastic coefficients at uniaxial compressive stress of a 24.5 MPa appear to be similar to the dynamic elastic coefficients under ambient condition. Although some deviations are observed, the preferred orientations of microcracks appear to be parallel or subparallel to the rift, the grain, and the hardway from microscopic observation of thin sections. This indicates that the preferred orientations of microcracks cause the elastic anisotropy of the Iksan Jurassic Granite. The results are to be applied to the effective use of the Iksan Jurassic Granite as stone materials, and can be used for the non-destructive safety test.

• Journal of the Korean Magnetics Society
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• v.7 no.4
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• pp.191-195
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• 1997

$Co_{84}Hf_{16}$ (1300$\AA$, 2150$\AA$) thin films were prepared by dc magnetron sputtering method. To investigate the uniaxial anisotrpy of the sample, the saturation and effective magnetization of the thin films were measured by VSM and FMR, respectively. The spectroscopic splitting g factor were estimated from the ferromagnetic resonance curves. For 1300$\AA$, 2150$\AA$, the effective magnetization was measured at the temperatures from T=77K to T=300K. The results were analyzed in terms of Bloch's law $M_s(T)=M_s(0)(1BT^{3/2}CT^{5/2}$. The Bloch coefficient B and C were determined by fitting. $M_{eff}(0)$ was obtained by extrapolating $M_{eff}$ to 0 K. From this result, the spinwave stiffness constants D was also determined and the exchange stiffness constants $A_{eff}$ were calculated by Kittel's resonance conditions.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.213-225
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• 2009

The purpose of the study is to evaluate the effects of chemical weathering on the granite and orthogneiss in Wonju area based on accelerated artificial chemical weathering. The rock samples were scrutinized the variation of index properties and ion exchanges caused by artificial chemical weathering which was implemented with leaching test for 170 days using double soxhlet extractor. The differential weathering and decrease of p wave velocity were obtained by weathering process without significant changes of porosity. In case of granite samples, the uniaxial compression strength was reduced by 20% and 16% for the F-grade and SW-grade, respectively. For MW-grade granite, however, was not able to examine the effect of strength reduction due to lack of sample number. Also, for orthogneiss, it is difficult to compare the values of uniaxial compressive strength between before and after the test because of its strong anisotropy.

• The Journal of Engineering Geology
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• v.26 no.4
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• pp.593-600
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• 2016

To understand the mechanical properties of rock masses and intact rock in Korea, data from 4,280 in situ and laboratory tests from 107 tunnels on general national roads were analyzed. The mechanical properties (unit weight, cohesion, friction angle, modulus of deformation, Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, coefficient of permeability, and specific gravity) were analyzed by rock types and strength of rock in each rock type. The results of analysis, the mean specific gravity was highest in gneiss. The coefficient of permeability and Poisson's ratio show the highest mean values in granite and metamorphic rock, respectively. In addition, the unit weight, cohesion and friction angle in sedimentary rock, modulus of deformation, Young's modulus, uniaxial compressive strength and tensile strength in volcanic rock have the highest mean values. The values for each mechanical property showed wide ranges by the heterogeneity and anisotropy of rock masses in spite of detailed analysis by rock type and classification of rocks according to the strength.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.313-321
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• 2000

This paper deals with a kind of the half-space interfacial problem in time domain, requiring the calculation of the horizontal electric field generated by a tiny impulsive current source located horizontally at the interface between an isotropic upper half-space and a uniaxially anisotropic lower half-space. With the Cagniard-de-Hoop method adapted for our interfacial case, we obtain the explicit-form solution for this electric field. We also investigate the impulse radiation in the radial direction. The impulse components of Dirac $\delta$-function type in transient waveforms are important for the understanding of the interfacial far-field characteristics. The uniaxial case is a generalization of the isotropic one, and the explicit solutions of the uniaxial problem in this paper reduce to the solutions of the isotropic problem if the anisotropy is removed.

• Journal of the Korean Magnetics Society
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• v.11 no.2
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• pp.45-49
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• 2001

Effects of multilayer structure and annealing condition on the soft magnetic properties of sputtered Fe/CoNbZr multilayers were investigated. We observed a minimum coercivity (1.1 Oe) at 5 nm thick Fe layer and the maximum permeability (2300) at 15 nm Fe layer and high saturation magnetization in the as-deposited state. As a result of increase of Fe grain size, coercivity increases with increasing Fe layer thickness. Degradation of ${\mu}$ at the thin Fe layer region may be due to the intermixed phase of high magnetostriction, such as CoFe. Optimum annealing condition was obtained through annealing at 300 $^{\circ}C$ for 40 min (${\mu}$=2500, H$\sub$c/=0.35 Oe). Enhancement of permeability was observed in the temperature range of 250∼300$^{\circ}C$. These results may closely be related with lowering the anisotropy energy by lattice deformation (0.4%) and enhanced uniaxial anisotropy.

• Journal of Magnetics
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• v.17 no.1
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• pp.1-5
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• 2012

The coercivity of a single 27 nm-spherical barium ferrite (S-BaFe) particle was simulated using three models: 1) Gibbs free energy (GFE), 2) Landau-Lifshitz-Gilbert (LLG), and 3) Stoner-Wohlfarth (S-W). Spherically and hexagonally shaped particles were used in the GFE and LLG simulations to investigate coercivity with the different shape anisotropies. The effect of shape was not included in the S-W model. It was found that the models using a spherical shape resulted in a coercivity higher than the models using the hexagonal shape with both shapes having the same diameter. The coercivity estimated with the S-W model was approximately the same as that for the spherical-shape models, which indicates that spherical shape has no significant effect on the particle's coercivity at nanoscale.

• Korean Journal of Materials Research
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• v.5 no.8
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• pp.1040-1044
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• 1995

Magnetic garnet films of (YSmLuCa)$_3$(FeGe)$\_$5/O$\_$12/ have been grown by the liquid phase eqitaxy method on the substrate of non-magnetic garnet Gd$_3$Ga$\_$5/O$\_$12/. The variation of Sm ion concentration were varied 0.3, 0.4, 0.6, mole/formula unit respectively. The magnetic properties of the samples for the bubble magnetic materials, such as, line width ΔH of ferromagnetic resonance (FMR), magnetic saturation induction 4$\pi$Ms, wall mobility u$\_$w/ uniaxial magnetic anisotropy energy Ku, were measured and discussed the relations between these properties. The line width ΔH decreases with increasing 4$\pi$Ms, and with decreasing Sm concentration. The anisotropy energy Ku increases not only with increasing Sm ion concentration, but also increasing 4$\pi$Ms. The value of wall mobility u$\_$w/ increase with increasing 4$\pi$Ms and decreases with increasing Sm concentration. We define a physical constant Eι from the fact that the product of 4$\pi$Ms and ΔH is constant with dimension of energy density. The Eι is dependent only on Sm concentration.density. The Eι is dependent only on Sm concentration.