• Journal of Magnetics
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• v.16 no.4
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• pp.453-456
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• 2011

Demagnetization for a tube sample which was made of a galvanized steel sheet was performed by applying a magnetic field with a decrement to remove the remanent magnetization of the material. An orthogonal fluxgate magnetic field sensor was used to measure a magnetic field created from a ferromagnetic material. To evaluate the remanent magnetization, the measured magnetic fields were separated into two magnetic field components by the remnant magnetization and the induced one. The horizontal and the vertical bias fields should be controlled separately during demagnetization to remove the horizontal and the vertical components of the remanent magnetization of the tube sample.

• 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 Magnetics
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• v.4 no.1
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• pp.17-21
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• 1999

The GMR ($d_Cu$) oscillatory behaviour as well as the widths of first and the second antiferromagnetically coupled ranges of the Permalloy ($Py=Ni_{83}Fe_{17}$)/Cu multilayers have been found to be strongly affected not only by the presence of the superparamagnetic/paramagnetic entitles located at the Py/Cu interfaces but mainly by the existence of the magnetic bridges between Py layers. The effectiveness of the magnetic bridges has been found to be temperature dependent, leading to the temperature dependence of the remnant to saturation magnetization ratio ($M_R/M_S$). We have found that for Py/Cu multilayers with equal Py and Cu layer thicknesses a high field sensitivity of the GMR effect (0.4%/Oe) and negligible hysteresis can be achieved when the number of Py layers decreases from 100 to 6. Sensitivity can be further improved by increasing the Py layers thickness, but the hysterstic effect becomes more pronounced then.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.659-662
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• 1995

Co-ferrite ($CoO-Fe_{2}O_{3}$) thin films have been prepared by two ways of low temperature solid reaction including oxidation process, being based on $Co-layer/{\alpha}-Fe_{2}O_{3}$ films and $Co-layer/Fe_{3}O_{4}$ films. Magnetic properties of both Co-ferrite films have been measured and compared. The samples from $Co-layer/Fe_{3}O_{4}$ films have a large coercive force in the direction perpendicular and have a great poler kerr rotation angle at wavelength 700 nm than ones from $Co-layer/{\alpha}-Fe_{2}O_{3}$ films. The typical magnetic properties are as follows; saturation magnetization $4{\pi}Ms$, 2.9 kG; remnant magnetization $4{\pi}Mr$, 2.0 kG; coercive force Hc, 4.0 kOe; kerr rotation angle ${\PHI}k$, 0.39 deg($\lambda\;=\;700\;nm$); and initial magnetization energy E, $3.3\;{\times}\;10^6\;erg/\textrm{m}^3$, respectively.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.900-904
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• 1995

We have developed a new torque magnetometric method for measuring the M-H hysteresis loop of a spheroid-shape magnetic material having a uniaxial anisotropy. Our torque magnetometric method gives the saturation magnetization as well as the remnant magnetization, simultaneously. A torque magnetometer having the torque sensitivity of $10^{-6}$ dyn cm could give the extreamly high sensitivity of $10^{-9}$ emu in measuring the magnetic moment, which is high enough to measure the magnetic moment of a monolayer Ni film. The accuracy of the present method was negligibly affected even at the applied fields near the coercivity where magnetization was inhomogeneous.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.231-236
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• 2000

In order to predict depth of the pile forward modeling and inversion of magnetic logging data was conducted by using a finite line of dipoles model. The horizontal component as well as the vertical component of magnetic fields can be measured in the borehole, and the magnetic anomalies can be obtained by subtracting the Earth's magnetic field from the measurement. The magnetic anomalies of the pile are considered as vector sum of induced magnetization due to the Earth's magnetic field and remnant magnetization possessed by steel strings in the pile. The magnetic anomalies are used as input data for inversion from which the length, the magnetic moment per unit length, and the dip angle of the pile can be obtained. From the inversion of synthetic noisy data, and the data obtained from the field model test it is found that the driving depth of the pile can be determined as close to the order of measuring interval (5∼10㎝). It is also found that the resultant magnetic anomalies due to an individual steel string in the pile are almost same as those due to a group of steel strings located at the center of the pile. The magnetic logging method also can be used for locating reinforced bars, pipes, and steel casings.

• Journal of the Korean Geophysical Society
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• v.2 no.2
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• pp.135-142
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• 1999

Interpretations of 3-component magnetic logging data obtained for a reinforced bar as a model of the line of the magnetic dipoles are conducted using a least squared inversion technique. The length of the bar is 1.12 m, sampling interval is 0.05 m, the distance between the bar and the borehole is 0.3 m, and the top of the bar is fixed at 0 m of depth. The bar is set to be approximately vertical. Magnetic anomalies smoothed with FFT are used as input data for the inversion. For the interpretation of magnetic logging data the depth to the top, the length, the magnetic moment per unit length, the direction of the magnetization (declination and inclination), and the bearing and plunge of the line of magnetic dipoles are left as unknown parameters. The comparison of the results obtained from the individual inversion of the horizontal component or the vertical component of the magnetic anomalies, and those from the simultaneous inversion of horizontal and vertical component of the magnetic anomalies shows that there exist some disagreements between each inversion result. The depth to the bottom of the bar, which is actually 1.12 m, is estimated as 1.18 m, and the inclination of the magnetization is estimated as -76°by simultaneous inversion. The negative value of the inclination indicates that the strength of the remnant magnetization is much greater than that of the induced magnetization, so that the direction of the resultant magnetization points to the top of the bar.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.653-656
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• 2004

We report the magnetic properties, microstructures, and crystal orientations of the CrO$_2$ thin films on TiO$_2$ single crystals. CrO$_2$ thin films were deposited by thermal decompositions with CrO$_3$ source materials. The microstructure of (110) oriented CrO$_2$ thin films deposited on (110) TiO$_2$ single crystals were uniform. As the oxygen flow rates increased, the resistivity, coercive field, and remnant magnetization of the CrO$_2$ thin films on TiO$_2$ single crystals decreased.

• Geophysics and Geophysical Exploration
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• v.23 no.1
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• pp.22-37
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• 2020

We analyze the comprehensive three-dimensional (3D) magnetic structure characteristics from the seafloor to the deep layer of the Tofua Arc (TA) 12 seamount in the Tonga Arc, Southwestern Pacific, using bathymetric and geomagnetic data, and magnetization vector inversion (MVI) results. The seafloor features surrounding TA 12 highlight a NW-SE-oriented elliptical caldera at the summit of the seamount, two small cones in the depressed area. A large-scale sea valley is present on the western flank of the seamount, extending from these caldera cones to the southwestern base of the seamount. TA 12 seamount exhibits a low magnetic anomaly in the caldera depression, whereas a high magnetic anomaly is observed surrounding the low magnetic anomaly across the caldera summit. It is therefore presumed that there may be a strong magnetic material distribution or magma intrusion in the caldera. The 3D MVI results show that the high anomaly zones are mainly present in the surrounding slopes of the seamount from the seafloor to the -3,000 m (below the seafloor) level, with the magnetic susceptibility intensity increasing as the seafloor level increases at the caldera depression. However, small high anomaly zones are present across the study area near the seafloor level. Therefore, we expect that the magma ascent in TA 12 seamount migrated from the flanks to the depression area. Furthermore, we assume that the complex magnetic distribution near the seafloor is due to the remnant magnetization.

• The Journal of the Korea Contents Association
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• v.8 no.12
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• pp.214-221
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• 2008

Terrestrial magnetism has left traces through residues such as fossils of the terrestrial magnetism as time went by. An analysis of archaeological terrestrial magnetism is an estimation of dates of archaeological remains where baked earth is exposed by measuring the change of the past terrestrial magnetism through thermo-remnant magnetization of baked earth. This paper attempts to apply an analysis of the archaeological terrestrial magnetism to archaeological remains using fourteen soil samples extracted from a charcoal kiln with side window located at the Area Ⅰ of Maegokdong. The date of A.D.440${\pm}$15 the analysis of archaeological terrestrial magnetism came up with gives solid evidence, while an archeological chronicle used arrangements of surrounding artifacts because of the absence of remains and assumed uncertainly that a charcoal kiln with side window was from the three kingdom periods. This analysis of archaeological terrestrial magnetism has come to anchor as a main natural scientific analysis because it relatively easily removes pollutants and comes up with highly reliable results owing to its considerably narrow error tolerance of assumed dates.