• Journal of the Korean Magnetics Society
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• v.11 no.5
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• pp.179-183
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• 2001

Magnetoresistance and Planar Hall effect of Glass/Ni$\sub$83/Fe$\sub$17/(2 nm)/[Cu(2 nm)Ni$\sub$83/Fe$\sub$17/(20 nm)]$\sub$50/ multilayer were measured. Repeated saw tooth like planar Hall effect signal was observed in the range of magnetization reversal process, while no sign of such saw tooth was observed in Magnetoresistance diagram. For the reason of saw tooth like signal, it is supposed that subsequent abrupt domain wall motion of each magnetic layer in the process of magnetization reversal process was observed in planar Hall effect in transverse direction to the current direction. This fine structure of planar Hall effect was observed for applied fields in any direction. Magnetoresistance curve did not show this fine structure of magnetization reversal, of course, since only net magnetization of each layer has to do with the resistivity. Extended research on the reason of this sawtooth like signal should be conducted.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.305-308
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• 2006

Magnetic flux leakage (MFL) pigs are traditionally used for the detection of gross corrosion on steel pipelines used for the transmission of natural gas. Alternative nondestructive evaluation (NDE) modalities are required for the detection of stress corrosion cracking (SCC) which tends to exist in colonies oriented axially along the length of the pipeline. This paper describes the use of multiphase rotating magnetic fields in the remote region of the probe as a possible SCC detection mechanism. Details of a prototype pig and test rig are given and the challenges associated with the finite element modeling of the device are discussed. Initial experimental results show that this novel NDE modality is sensitive to axially oriented tight cracks.

• Journal of the Korean Magnetics Society
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• v.8 no.3
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• pp.118-124
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• 1998

$Ni_{0.65}Zn_{0.35}Cu_{0.1}Fe{1.9}O_4$ has been studied with Mossbauer spectroscopy and X-ray diffraction. The crystal structure is found to be a cubic spinel with the lattice constant $a_0=8.390{\AA}$. Mossbauer spectra of $Ni_{0.65}Zn_{0.35}Cu_{0.1}Fe{1.9}O_4$ has been taken at various temperatures ranging from 12 K to 705 K. The isomer shift indicates that iron ions are ferric at tetrahedral [A] and octahedral sites [B], respectively. The Neel temperature is determined to be $T_N=705\;K$. As the temperature increases toward $T_N$ a systematic line broadening effect in the Mossbauer spectrum is observed and interpreted to originate from different temperature dependencies of the magnetic hyperfine fields at various iron sites. The quadrupole splitting just on $T_N$ is 0.41 mm/s whereas the quadrupole shift below $T_N$ vanishes. This implies that the orientation of the magnetic hyperfine field with respect to be principal axes of the electric field gradient is random.

• Journal of Magnetics
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• v.10 no.1
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• pp.5-9
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• 2005

Nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ is fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with XRD, SEM, Mossbauer spectroscopy, and VSM. $Ni_{0.9}Zn_{0.1}Fe_2O_4$ powders annealed at $300{^{\circ}C}$ have a spinel structure and behaved superparamagnetically. The estimated size of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 10 nm. The hyperfine fields at 13 K for the A and B patterns are found to be 533 and 507 kOe, respectively. The ZFC curves are rounded at the blocking temperature ($T_B$)and show a paramagnetic-like behavior above $T_B$. $T_B$ of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 250 K. Nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at 400 and $500{^{\circ}C}$ have a typical spinel structure and is ferrimagnetic in nature. The isomer shifts indicate that the iron ions were ferric at the tetrahedral (A) and the octahedral (B). The saturation magnetization of nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at 400 and $500{^{\circ}C}$ are 40 and 43 emu/g, respectively. The magnetic anisotropy constant of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at $300{^{\circ}C}$ were calculated to be 1.6 ${\times}$ $10^6$ ergs/$cm^3$.

• Journal of Magnetics
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• v.2 no.3
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• pp.76-85
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• 1997

Magnetic and magnetostrictive properties of Tb-Fe and Tb-Fe-B thin films are systematically investigated over a wide composition range from 40.2 to 68.1 at. % Tb. The films were fabricated by rf magnetron sputtering using a composite target which consists of an Fe plate and Tb chips. The microstructure, examined by X-ray diffraction, mainly consists of an amorphous phase and, at high Tb contents, a pure Tb phase also exists. A progressive change in the direction of anisotropy from the perpendicular to in-plane occurs as the Tb content increases and the boundary at which the anisotropy change occurs shifts significantly towards to higher Tb contents with the addition of B. The saturation magnetization exhibits maxima at the Tb contents of 42 and 48 at. % for Tb-Fe and Tb-Fe-B thin films, respectively, and it is decreased by the addition of B. The coercive force, measured in the easy direction, decreases monotonically with the Tb content. Excellent magnetostrictive characteristics, particularly at low magnetic fields, are achieved in both Tb-Fe and Tb-Fe-B thin films; for example, a magnetostriction of 138 ppm is obtained in a Tb-Fe-B thin film at a magnetic field as low as 30 Oe. The excellent magnetostrictive properties of the present thin films are supported by the equally excellent magnetic softness, the coercivity below 10 Oe and a typical squared-loop shape with the saturation field as low as 1 kOe. Due to the excellent low field magnetostrictive characteristics, the present Tb-Fe based thin films are thought to be suitable for Si based microdevices.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.7-16
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• 1999

Stoichiometric and nonstoichiometric $Y_{3-x}Fe_{5+x}O_{12})$ polycrystalline samples (x=0.00, 0.05, 0.10, 0.30, -0.05, -0.10, -0.30) were prepared by solid state reaction method. The magnetic properties of the sample were investigated by FMR (ferromagnetic resonance) technique at microwave frequency 5.11 GHz (G-band) and 23.39 GHz (K-band) respectively. The spectroscopic splitting factor g were estimated to be 2.04~2.35 from the derivative absorption lines. As the samples became yttrium $(Y^{3+})$ excess and iron $(Fe^{3+})$ excess, Magnetizations were decreased. But resonance linewidth were increased. To investigate the anisotropy, the angular dependence of resonance magnetic fields were measured. Angular dependence of effective magnetizations were measured by FMR from 77 K to 300 K at K-band microwave frequency (23.39 GHz) and the saturation magnetizations were measured by VSM. The Bloch coefficients B and C were determined by fitting. $M_{eff}(0)$ was obtained by the extrapolation from 80 K. From this result, the spin wave stiffness constant D $(about\; 162~206 \;eV{\AA}^2)$and average square range of exchange interaction $$$(about \;5.84~12.13\;{\AA}^2)$ were determined.

• Journal of Magnetics
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• v.7 no.1
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• pp.18-20
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• 2002

The charge structures of (LSMO) and of the combined system $(La_{ 0.6}Sr_{0.4}FeO_3$(LSMO) and of the combined system (La_{0.6}Sr_{0.4}MnO_3)_{0.7}(La_{0.6}Sr_{0.4}/FeO_3)_{0.3}$are investigated by using M$\ddot{o}$ssbauer spectroscopy. The antiferromagnetically ordered $(La_{0.6}Sr_{0.4}FeO_3$(LSFO) has possible charges of Fe^{3+} and Fe^{4+}$, which include a low-spin $Fe^{4+}$ state at and above 230 K. The temperature dependences of the M$\ddot{o}$ssbauer spectra for the $(La_{ 0.6}Sr_{0.4}FeO_3$ system and for the combined $(LSMO)_{ 0.7}(LSFO)_{0.3}$ system are fitted as three sets of Zeeman patterns corresponding to $Fe^{3+}$ and $Fe^{4+} below 230 K. At and above 230 K, the fitted M$\ddot{o}$ssbauer spectra for the combined system are the same in all temperature ranges. Above 230 K, $(La_{0.6}Sr_{0.4}FeO_3$ spectrum consists of two sets of six Lorentzians for $Fe^{3+}$ and one line for low spin $Fe^{4+}$. It is worth noting that large fields are induced in the combined system.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.778-781
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• 1995

The mixed ferrite $Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been investigated by X-ray and $M\"{o}ssbauer$ spectoscpy. From the results of X-ray diffraction measurement the structure for this system is spinel, and the lattice constant is in accord with Vegard's law. $M\"{o}ssbauer$ spectra of $Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been taken at various temperature ranging from 13 to 800 K. The isomer shifts indicate that the valence states of the irons at both A(tetrahedral) and B(octahedral) sithe are found to be in ferric high-spin states. The variation of magnetic hyperfine fields at the A and B sites are explained on the basis on A-B and B-B supertransferred hyperfine interactions. It is found that Debye temperatures for the A and B sites of $CoFe_{2}O_{4}$ and $NiFe_{2}O_{4}$ are found to be ${\theta}_{A}=734{\pm}5K,\;{\theta}_{B}=248{\pm}5K,\;and\;{\theta}_{A}=378{\pm}5K,\;{\theta}_{B}=357{\pm}5K$, respectively. Atomic migration of $Ni_{0.3}Co_{0.7}Fe_{2}O_{4}$ starts near 450 K and increases rapidly with increasing temperature to such a degree that 61 % of the ferric ions at the A site have moved over to the B site by 700 K.

• Journal of the Korean Magnetics Society
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• v.5 no.6
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• pp.968-973
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• 1995

In order to investigate the annealing effect for RF magnetron sputtered $Ni_{83}Fe_{17}$ thin films, we have studied the spin wave rehaviors by FMR after annealing the samples at $135^{\circ}C,\;225^{\circ}C$ in air and at $160^{\circ}C,\;220^{\circ}C,\;330^{\circ}C,\;390^{\circ}C\;and\;420^{\circ}C$ in argon gas for one hour respectively. In FMR spectra for the films annealed in argon gas and the assputtered film at perpendicular resonance, only odd numrer spin waves are observed. But even numrer spin waves are observed for the film annealed in air at $225^{\circ}C$ recause of the large difference retween both surface magnetic anisotropy. In the case of the sample annealed at $420^{\circ}C$ in argon gas, the spin waves are shifted toward high field, can due to the increase of saturation magnetization during annealing. The spacings retween the spin wave resonance fields are narrowed rapidly, this is thought that the magnetic homogeneity increased in the film after annealing at high temperature.

• Journal of Magnetics
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• v.5 no.4
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• pp.120-123
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• 2000

Co-Ni-Fe-N thin films were fabricated by a $N_2$ reactive rf magnetron sputtering method. The nitrogen partial pressure ($P_{N2}$) was varied in the range 0~10% . As$P_{N2}$ increases in this range, the saturation magnetization $B_s$ linearly decreases from 19.8 kG to 14 kG and the electrical resistivity ($\rho$) increases from 27 to 155 $\mu\Omegacm$. The coercivity $H_c$ exhibits the minimum value at 4% $P_{N2}$. The magnetic anisotropy fields ($H_k$) are in the range of 20$\sim$50 Oe. High frequency characteristics of $(Co_{22.2}Ni_{27.6}Fe_{50.2})_{100-x}N_x$ films are excellent in the range of 3$\sim$5% of $P_{N2}$. In particular, the effective permeability of the film fabricated at 4% $P_{N2}$ is 800, which is maintained up to 600 MHz. This film also shows Bs of 17.5 kG, $H_c$/ of 1.4 Oe, resistivity of 98$\mu\Omegacm$ and $H_k$ of about 25 Oe. Also, the corrosion resistance of $(Co_{22.2}Ni_{27.6}Fe_{50.2})_{100-x}N_x$ films was imp roved with increasing N concentration.