• Proceedings of the KIEE Conference
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• 2005.10c
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• pp.50-52
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• 2005

In this paper, the analysis of the eddy current testing(ECT) signals under thc Influence of the ferromagnetic support plate was performed in steam generator(SG) tube of nuclear power plant. In order to remove the influence of the ferromagnetic support plate, a multi-frequency ECT was used. The models which was established for the analysis of the signals is calculated using numerical analysis of finite element method. Through the result of numerical analysis, improved signals is acquired considering the influence of the ferromagnetic support plate using mixing of multi-frequency This paper is presented the residual errors and the phase changes for analysis of the defect signals which should be considered when conducting a ECT using multi-frequency.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.11-13
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• 2006

[ $M\"{o}ssbauer$ ] spectra of $Ti_{1-x-y}Co_xFe_yO_2(0.01{\leq}x,\;y{\leq}0.05)$ prepared with $^{57}Fe$ enriched iron have been taken at various temperatures ranging from 80 to 300K. The Mossbauer spectrum of $Ti0.94Co_{0.03}Fe_{0.03}O_2$ consists of a ferromagnetic (six-Lorentzian), a paramagnetic phase (doublet) and armorphous phase over all temperature ranges. Isomer shifts indicate $Fe^{3+}$ for the ferromagnetic phase and the paramagneic phase of $Ti_{1-x-y}Co_xFe_yO_2$ samples. It is noted that the magnetic hyperfine field of ferromagnetic phase had the value about 1.5 times as large as that of u-fe. The XRB data for $Ti_{1-x-y}Co_xFe_yO_2$ showed mainly rutile phase with tetragonal structures without any segregation of Co and Fe into particulates within the instrumental resolution limit. The magnetic moment per (Co+Fe) atom in $Ti0.94Co_{0.03}Fe_{0.03}O_2$, under the applied field of 1T was estimated to be about $0.332{\mu}_B$ which is ten times as large as that of $Ti0.97Co_{0.03}Fe_{0.03}O_2,\;0.024{\mu}_B$ per Co atom, suggesting a high spin configuration of Co and fe ions.

• Journal of the Korean Magnetics Society
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• v.13 no.6
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• pp.237-242
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• 2003

$Ti_{1-x}$$^{57}$ F $e_{x}$ $O_2$(0.0$\leq$x$\leq$0.07) compounds were fabricated using the sol-gel method, and the crystal structure and magnetic properties were investigated as a function of doped $^{57}$ Fe concentration. X-ray diffraction patterns showed a pure anatase single phase, without any segregation of Fe into particulate. With varying $^{57}$ Fe concentration, we could observe unusual magnetic phenomena in these materials. Doping $^{57}$ Fe into the Ti $O_2$ nonmagnetic semiconductor formed magnetic properties, but the gradual increase of $^{57}$ Fe concentration decreased rapidly the ferromagnetic properties rather than enhanced the ferromagnetic properties. Obvious ferromagnetic behavior was shown for the samples with x$\leq$0.01, while paramagnetic behavior was shown for the sample with x$\geq$0.03. These phenomena could be verified using Mossbauer measurement. Separation of the ferromagnetic phase (sextet) and the paramagnetic phase (doublet) of the samples with different $^{57}$ Fe concentration was characterized. Samples with x$\leq$0.01 have sextet and doublet simultaneously, but samples with x$\geq$0.03 have only doublet at room temperature. This indicates that the sample x$\leq$0.01 have the ferromagnetic phase at room temperature. This result corresponded with the M-H loops referenced above and reveals an interesting feature that there is a critical limit of $^{57}$ Fe concentration (0.01$\leq$0.01 samples was fundamentally attributable to the paramagnetic phase as well as the ferromagnetic phase.e.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.3
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• pp.257-262
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• 2001

Single crystalline films of La doped YIG(yttrium iron garnet) were grown by the liquid phase epitaxy. The lattice constants of films obtained by DCD(double crystalline diffractometer) measurement increased with increasing La contents in films. In particular, lattice constants of films grown wiht Y/La=20 solution were nearly same as those of GGG (gadolinium gallium garnet) substrate. The saturation magnetization measured with VSM (vibrating sample magnetometer) was about 1750Gauss which is the same as that of pure YIG irrespective of La contents in films. FMR(ferromagnetic resonance) linewidth of La doped YIG was smaller than that of pure YIG. Since appropriate La doping decreases the lattice mismatch between film and substrate, the FMR linewidth was Y/La=20 in this experiment.

• Journal of the Korean Magnetics Society
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• v.8 no.4
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• pp.179-184
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• 1998

Colossal magnetoresistance is closely related to (but is not) the abrupt change of electrical resistivity in the vicinity of Curie temperature, which is caused by the temperature dependent paramagnetic-ferromagnetic phase transition and concurrent change of electrical conducting mechanism. A resistivity-temperature equation is presented to fully describe the overall behavior, especially the abrupt change. The main ingredients of the equation are a simple effective media theory and a function for the temperature dependent fraction of ferromagnetic phase. The model fits very well to the measured resistivity-temperature curve of $La_{0.7}Ca_{0.3}MnO_3$.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.703-709
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• 2006

We report on the synthesis of highly uniform, single phase zinc and cobalt thin films prepared by the Liquid Phase Deposition (LPD) method. X-Ray diffraction, TGA and EDX measurements support the assumption that the as deposited films are constituted by a mixture of crystallized FeOOH and amorphous M(OH)$_2$ (M=Co, Zn) which is converted upon heat treatment in air at 600?C into the corresponding zinc ferrites. The films with adjustable chemical compositions are identified with a crystal structure as spinel-type and present a spherical or rod-like microstructure, depending on the both the nature and concentration of the divalent transition metal ions. Zinc ferrite thin films present a superparamagnetic behavior above blocking temperatures which decrease with increasing the Zn content and are ferromagnetic at 5 K with coercivities ranging between 797.8 and 948.5 Oe, whereas the cobalt ferrite films are ferromagnetic at room temperature with magnetic characteristics strongly dependent on the chemical composition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.375-377
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• 1998

The magneto-optical properties of Co/Co$_2$TiSn two-phase magnet films were studied. These films show that relatively large Kerr rotations which are -0.4 deg. at the wavelength of 400 nm, compared to that of pure Co. It is conceivable that the magneto-optical effects may be due to both contributions of ferromagnetic Co matrix and ferromagnetic Co$_2$TiSn Heusler alloy precipitate. The perpendicular magnetization curve domonstrates a typical bubble domain hysteresis loop. the saturation magnetization change of the annealed film is less sensitive to temperature in the low temperature region and the Curie temperature of Co$_2$TiSn Heusler alloy precipitate is a little higher in the annealed film. These can be explained by the increase of the number of Co-Co exchange interaction in Heusler alloy structure resulting from the change of chemical ordering by annealing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.155-159
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• 2003

Polycrystalline $Ti_{1-x}Co_xO_2$ thin films on $SiO_2$ (200 nm)/Si (100) substrates were prepared using liquid-delivery metalorganic chemical vapor deposition. Microstructures and ferromagnetic properties were investigated as a function of doped Co concentration. Ferromagnetic behaviors of polycrystalline films were observed at room temperature, and the magnetic and structural properties strongly depended on the Co distribution, which varied widely with doped Co concentration. The annealed $Ti_{1-x}Co_xO_2$ thin films with $x{\leq}0.05$ showed a homogeneous structure without any clusters, and pure ferromagnetic properties of thin films are only attributed to the $Ti_{1-x}Co_xO_2$ (TCO) phases. On the other hand, in case of thin films above x=0.05, Co clusters formed in a homogeneous $Ti_{1-x}Co_xO_2$ Phase, and the overall ferromagnetic (FM) properties depended on both $FM_{TCO}$ and $FM_{Co}$. Co clusters with about 10nm-150nm size decreased the value of Mr (the remanent magnetization) and increased the saturation magnetic field.

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.12.2-12.2
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• 2008

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.51.1-51.1
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• 2008