• Korean Journal of Materials Research
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• v.4 no.1
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• pp.55-62
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• 1994

Co(A $I_{1- X}$C $u_{X}$ ) (0$\leq$0.40)합금계의 결정구조 및 자기적 특성을 X-선 회절분석기, 주사전자현미경 그리고 진동 시료형 자력계를 이용하여 조사하였다. X-선 결정구조 및 상분석 결과, 전조성 범위에서 주상은 격자상수가 약 2.86$\AA$인 규칙화한 B2(CsCI)구조를 가지고 있었으며, x $\geq$0.10범위에서는Cu함량이 많은 제 2상이 존재하였고 격자상수가 약 3.63$\AA$인 FCC 구조이었다. 자화측정결과 x $\geq$0.25범위에서는 강자성, x$\leq$0.10에서는 상자성 그리고 x=0.15, 0.20에서는 초상자성의 특성을 나타내었다. Cu함량(x)이 증가함에 따라 자화값은 증가하는 현상을 보여주었다. 본 합금계의 측정한 분자당 스핀자기 모멘트 값은 국부환경모델을 이용하여 각 조성에서 계산된 Co원소에 대한 스핀자기 모멘트 값과 잘 일치함을 보여주었다.다.

• Journal of the Korean Chemical Society
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• v.27 no.3
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• pp.224-232
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• 1983

The effects of ball-milling time on solid state reactions in the system $BaCO_3-Fe_2O_3$ and the magnetic properties of Ba-ferrite 4(BaFe_{12}O_{19})$ have been studied. $BaCO_3-Fe_2O_3 $mixtures were prepared by ball-milling for varying lengths of time; 5, 15, 30, 80 and 200 hours. Techniques employed were thermogravimetry, X-ray diffraction analysis, scanning electron microscopy and B-H curve tracer. It is shown that the aggregation states and superparamagnetic size fractions obtained by increasing ball-milling time have remarkable effects on solid state reactions and magnetic properties of Ba-ferrite.

• Korean Journal of Materials Research
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• v.2 no.2
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• pp.143-150
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• 1992

Crystal structures and magnetic properties of annealed Co-(Al-Fe) alloys have been investigated. Annealed specimens showed superparamagnetism when x=0.05 and ferromagnetism when $x{\geq}0.10$. Magnetization increased as x increased. X-ray diffraction data revealed that specimens were single-phase in B2(CsCl) structure with constant lattice parameter $2.87{\AA}$. The experimental results were analized on the point of view of the local environmental effect of magnetic atoms.

• Journal of Biomedical Engineering Research
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• v.35 no.4
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• pp.105-110
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• 2014

For the combination of MRI and magnetic particle hyperthermia(MPH), we investigated the relative heating efficiency with respect to the strength of the static magnetic field under which the magnetic nanoparticles are to be heated by RF magnetic field. We performed nanoparticle heating experiments at the fringe field of 3T MRI magnet with applying the RF magnetic field perpendicularly to the static magnetic field. The static field strengths were 0T, 0.1T, 0.2T, and 0.3T. To prevent the coil heat from conducting to the nanoparticle suspension, we cooled the heating solenoid coil with temperature-controlled water with applying heat insulators between the solenoid coil and the nanoparticle container. We observed significant decrease of heat generation, up to 6% at 0.3T(100% at 0T), due to the magnetic saturation of the nanoparticles of 15 nm diameter under the static field. We think MPH is still feasible at low magnetic field lower than 0.3T if stronger RF magnetic field generation is permitted.

• Journal of the Korean Magnetics Society
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• v.24 no.5
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• pp.135-139
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• 2014

Iron-oxide nanopowders were synthesized by a pulsed wire evaporation (PWE) in various ambient gas conditions. SEM measurement indicates that the spherical iron nanoparticles are about 50 nm in diameter. The phase analysis for the produced iron-oxide powders was systematically investigated by using $M\ddot{o}ssbauer$ spectra and the results show that classified phases of $Fe_2O_3$ and $Fe_3O_4$ can be controlled by regulating the oxygen concentration in the mixed gas during the PWE process. A quadrupole line on the center of $M\ddot{o}ssbauer$ spectrum represents the superparamagnetic phase of 12 % from ${\gamma}-Fe_2O_3$ phase.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.23-28
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• 1999

${\Alpha}-Fe_2O_3$ was accomplished by chemical method as low temperature as possible and the crystallographic and magnetic properties have been studied by Mossbauer spectroscopy and X-ray diffraction. The sample heated at 15$0^{\circ}C$ is found to have a Corundums symmetry with the hexagonal lattice constant a=8.26$\pm$0.05$\AA$, c=8.75$\pm$0.05$\AA$. The M$\"{o}$ssbauer spectra between the 4.2K and the room temperature show that the ${\Alpha}-Fe_2O_3$ crystallized with a single phase and fine sizes. The particle size distribution has the Gaussian distribution center at 98$\AA$ and the half width of 32$\AA$.TEX>.

• Korean Journal of Soil Science and Fertilizer
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• v.30 no.1
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• pp.3-15
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• 1997

Iron oxide compounds in 8 selected Cheju Island soil samples have been analized by X-ray fluorescence spectrometer(XRF), X-ray diffractometry(XRD), selected chemical techniques, and $M{\ddot{o}}ssbauer$ spectroscopy. The result of this analysis by XRF shows that the rate of quantity of $Fe_2O_3$ in 8 soil samples was from 8.03wt.%(Daejeong paddy soil) to 18.21wt.%(Songag soils). Songag, Heugag and Gueom soils were detected to have lower peaks of intensity of hematite by XRD. In addition, these soils were not detected to have hematite and goethite peaks. Ferrihydrite, which is a short-range-order mineral commonly present in volcanic ash soil, was not detected by XRD due to low concentration and/or poor cristallinity. Ferrihydrite contents estimated from Feo values were 8.8~35.2g/kg for volcanic ash soils and 0.85g/kg for the Daejeong soil. Most of the soil samples represented by the paramagnetic $Fe^{3+}$ doublet obtained from $M{\ddot{o}}ssbauer$ spectra at room temperature and 18K were considered to arise from the presence of ferrihydrite, superparamagnetic goethite, and silicate minerals. Also the paramagnetic $Fe^{2+}$ doublets are attributable to primary minerals such as olivine, illite, chlorite, augite, biotite, and hornblende. Goethite and hematite were identified as the dominant crystalline iron oxides in these soils from $M{\ddot{o}}ssbauer$ spectra obtained at room temperature and 18K. All the soil samples exhibited strong superparamagnetic relaxation. Collapse of the $M{\ddot{o}}ssbauer$ magnetic hyperfine splitting at room temperature was due to the small size(${\sim}180{\AA}$) of the oxide particles and/or Al-subsituted goethite.

• Journal of the Korean Magnetics Society
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• v.9 no.4
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• pp.177-183
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• 1999

Ultrafine $CoFe_{1.9}Bi_{0.1}O_4$ particles were fabricated by using a sol-gel method and their magnetic and structural properties were investigated with an x-ray diffractometer (XRD), a vibrating sample magnetometer (VSM), and a M$\"{o}$ssbauer spectrometer. The result of x-ray diffraction and M$\"{o}$ssbauer spectroscopy showed that the powders fired at and above 523 K had only cubic spinel structures. M$\"{o}$ssbauer spectra measurements showed that the powders annealed at 523,723 and 823 K possessed ferrimagnetic nature and paramagnetic nature due to superparamagnetism, simultaneously at room temperature and the powders annealed at and above 923 K behaved ferrimagnetically. In the case of the powder annealed at 923 K, the lattice constant was $a_0=8.398$\pm$0.005{\AA}$ and the hyperfine fields were $H_{hf}(A)=479kOe,\; H_{hf}(B)=502kOe$. The isomer shifts indicate that the iron ions are ferric at tetrahedral[A] and octahedral sites [B], respectively. The magnetization as a function of annealing temperature increased as increasing annealing temperature. The largest coercivity values were $H_C=1368\;Oe$ AT 923 K annealing temperature. In the case of the powder annealed at 1123 K, the magnetization value was $M_S=75\;emu/g$ and this value was similler to that of $CoFe_2O_4$.Fe_2O_4$.

• Journal of the Korean Chemical Society
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• v.38 no.8
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• pp.547-551
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• 1994

A series of samples in the $Nd_{1-x}Ba_xFeO_{3-y}$ system has been prepared by heating the reactants to$1200^{\circ}C$ under an ambient atmosphere, and the solid solutions were identified by X-ray power diffraction analysis. The crystal systems of samples with x = 0.00 and 0.25 were found to be orthorhombic whose local symmetry is similiar to the distorted octahedral with orthoferrite type one, whereas those with x = 0.50 and 0.75 to be the cubic system. Since Fe ions in the solid solutions are a mixed valence state between $Fe^{3+}\;and\;Fe^{4+}$ ions, the nonstoichiometric chemical formulas could be determined from the mole ratio of $Fe^{4+}$ ion and oxygen vacacies. According to the Mossbauer spectroscopic analysis, the presence of 5-coordinated $FeO_5$ was evidenced only in the barium compounds along with $FeO_6,\;and\;FeO_4$, but not in the strontium and calcium compounds. The samples with x = 0.25 and 0.50 show a spectrum of superparamagnetism, which might be due to the formation of a domain of the ferromagnetic interaction between the $Fe^{3+}\;and\;Fe^{4+}$ ions. The electrical conductivities of all samples are within semiconducting range. Since the $Fe^{4+}$ ion acts as an electron acceptor level during the electron transfer between the Fe through intermediate $O^{2-}$ ions, the activation energy of the compounds decreases with the increment of $Fe^{4+}$ content.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.102-106
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• 2006

Magnetic nanoparticles can be used for a variety of biomedical applications. They can be used in the targeted delivery of therapeutic agents in vivo, in the hyperthermic treatment of cancers. in magnetic resonance (MR) imaging as contrast agents and in the biomagnetic separations of biomolecules. We have synthesized magnetite $(Fe_3O_4)$ nanoparticles using chemical coprecipitation technique with sodium oleate as surfactant. Nanoparticle size can be varied from 2 to 8nm by controlling the sodium oleate concentration. Magnetite phase nanoparticles could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with sodium oleate and chitosan have been prepared. Nanoparticles, both oleate-coated and chitosan-coated, have been characterized by several techniques. Atomic farce microscope (AFM) was used to image the coated nanoparticles. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the magnetite nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles.