• Applied Chemistry for Engineering
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• v.31 no.1
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• pp.13-18
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• 2020

Iron oxide nanoparticles were microencapsulated using fibroin, a protein polymer of silk fiber, for theragnostic applications. The content of iron oxide was determined to be 4.28% by thermogravimetric analysis and 5.11% by magnetometer. A suspension of murine fibroblast 3T3 cells grown in medium supplemented with iron oxide-microcapsules turned clear in response to the magnetic force and the cells aggregated to the magnet direction. Neodymium magnets placed on the top of the culture dish, and attracted cells to the center of the culture surface. The cells collected on the culture surface aggregated to form a rough spheroid of 2 mm in a diameter after 72 h. In the outer layer of the cell aggregate, cells were relatively large and gathered together to form a dense tissue, but the central part was observed to undergo cell death due to the mass transfer restriction. In the outer layer, iron oxide-microcapsules were lined up like chains in the direction of magnetic force. Using microCT, it was demonstrated that the iron oxides inside the cell aggregate were not evenly distributed but biased to the magnetic direction.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.245-251
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• 2015

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental $Fe_2O_3$-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic ${\alpha}$-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that ${\alpha}$-Fe/MgO composite powders in which MgO is dispersed in ${\alpha}$-Fe matrix are obtained by MA of $Fe_2O_3$ with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the ${\alpha}$-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at $800{\sim}1000^{\circ}C$ under 60 MPa. X-ray diffraction result shows that the average grain size of ${\alpha}$-Fe in ${\alpha}$-Fe/MgO nanocomposite sintered at $800^{\circ}C$ is in the range of 110 nm.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.260-260
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• 2013

Multiferroic materials have attracted much attention due to their fascinating fundamental physical properties and technological applications in magnetic/ferroelectric data-storage systems, quantum electromagnets, spintronics, and sensor devices. Among single-phase multiferroic materials, $BiFeO_3 $ is a typical multiferroic material with a room temperature magnetoelectric coupling in view of high magnetic-and ferroelectric-ordering temperatures (Neel temperature $T_N$~647 K and Curie temperature $T_C$~1,103 K). Rare-earth ion substitution at the Bi sties is very interesting, which induces suppressed volatility of Bi ion and improved ferroelectric properties. At the same time, Fe-site substitution with magnetic ions is also attracting, and the enhanced ferromagnetism was reported. In this study, $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$ (x=0, 0.05 and 0.1) bulk ceramic compounds were prepared by solid-state reaction and rapid sintering. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ or 24 h to produce $Bi_{1-x}Dy_xFe_{0.95}Co_{0.05}O_3$. The samples were immediately put into an oven, which was heated up to $800^{\circ}C$ nd sintered in air for 30 min. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies).

• Journal of Astronomy and Space Sciences
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• v.17 no.1
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• pp.87-98
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• 2000

We examine the relative contributions of the electric field and ionospheric conductance to the auroral electrojets. For this purpose we used magnetometer data obtained from the International Magnetospheric Study (IMS) meridian chains of observatories for March 17, 18, and 19, 1978. Based on the study by Allen & Kroehl (1975), we redefine the AU and AL indices by utilizing the magnetic disturbance data obtained from the AE stations located within limited magnetic local time (MLT) sectors; i.e., $1500\leq MLT\leq1800$ and$0000\leq MLT\leq0300$, respectively. The current densities of the eastward and westward electrojets are calculated based on the AU and AL indices thus defined. Under the assumption that the Hall conductance at the dusk sector is mainly caused by the solar EUV radiation, we estimate the electric field contributin to the AU index. Assuming further that electric field distributins at dawn and dusk sectors are comparable, it is also possible to estimate the contribution of the Hall conductance associated at the dusk sector is mainly caused by the solar EUV radiation, we estimate the electric field contribution to the AU index. Assuming further that electric field distributions at dawn and dusk sectors are comparable, it is also possible to estimate the contribution of the Hall conductance associated with auroral particle precipitation to the AL index. From this study it is noted that the electric fields and Hall conductances thus estimated show significant correlations with the AU and AL indices, respectively, suggesting that the AU and AL indices are closely associated with the directly driven and loading-unloading processes of substorms.

• Geophysics and Geophysical Exploration
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• v.23 no.3
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• pp.208-214
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• 2020

In this study, we have developed a drone magnetic exploration system (proto-type) using a fluxgate magnetic sensor. Hardware of the system consists of a fluxgate magnetometer, an inertial measurement unit (IMU), a GPS, and a communication module. And we have developed monitoring software, which enables it to transmit the measured data to the ground control system (GCS) in real time. The measured magnetic data are finally saved as 1 Hz data after passing through a notch filter and a band-pass filter. For verification of this system, a preliminary test was conducted to check the magnetic responses of a magnetic object first, then the field test was carried out in two iron mines. We tested the developed system on the field test in Pocheon, Gyeonggi and Jeongseon, Gangwon. The magnetic data from the developed drone system was very similar to those from unmanned airship system developed by Korea Institute of Geoscience and Mineral Resources (KIGAM). As a result, preliminary experiment and field test have demonstrated that this system is applicable for outdoor aeromagnetic exploration. It requires more studies to improve filter function and instrument performance to minimize noise in the future.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.33-37
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• 2004

Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ has been studied with Mossbauer spectroscopy, x-ray diffraction, vibrating sample magnetometer (VSM), and magnetoresistance (MR) measurement. The crystal structure was determined to be a cubic spinel with lattice parameter a$_{0}$=9.9880 $\AA$. The MR measurements show a semiconductor behavior below 110 K and metal behaved above 100 K. The temperature dependence of magnetization of Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ was reported. In addition to a large irreversibility between the zero-field-cooling (ZFC) and the field-cooling (FC) magnetization at applied field H=100 Oe, a cusp-like anomaly was observed in both the FC and ZFC curves. It shifted toward the lower temperature region with increasing magnetic field, and then showed convex type maximum at 110 K, under the applied field of 5 kOe. The Mossbauer spectra were measured from 15 K to room temperature. The asymmetric line broadening was observed for the sample Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$, and it was considered to be dynamic Jahn-Teller relaxation. The charge state of Fe ions was ferrous in character. The unusual reduction of magnetic hyperfine field below 110 K was interpreted in terms of cancellation effect between the mutually opposite orbital current field (H$_{L}$) and Fermi contact field (H$_{C}$).

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.86-89
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• 2007

[ $FeCr_2Se_4$ ] prepared under the high pressure (3 GPa) has been studied with x-ray, neutron diffraction techniques, superconducting quantum interference device (SQUID) magnetometer, resistance, and Mossbauer spectroscopy. The temperature dependence of resistance is explained by Mott-VRH and small polaron model for the regions I (T<20 K) and II (T>42 K), respectively. Neutron diffraction results show an antiferromagnetic spin-lattice coupling near the Neel temperature. So finally the distance of atom is enlarged in region (110$FeCr_2Se_4$ shows convex type of temperature dependence.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.183-187
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• 2007

Compounds of multiferroic materials $YMn_{2-x}Fe_xO_5$ (x = 0.00, 0.01) were prepared using the sol-gel method. The crystallographic, magnetic and electric properties are studied using x-ray diffraction (XRD), neutron diffraction, vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The crystalline structure of $YMn_2O_5$ was found to be orthorhombic (Pbam) at room temperature. The lattice constants of $YMn_2O_5$ were determined to be $a_0=7.275\;{\AA},\;b_0=8.487\;{\AA},\;c_0=5.674\;{\AA}$. The lattice constants not changed with Fe concentrations. Our data demonstrate the correlation of magnetic and electric properties in $YMn_2O_5$ materials.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.106-106
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• 2014

SIGMA (Scientific cubesat with Instrument for Global Magnetic field and rAdiation)는 근 지구공간에서 우주방사선량 측정과 자기장 변화 검출의 과학적 목적과 교육적 목적을 가지고 개발하고 있는 초소형 큐브위성이다. $100mm{\times}100mm{\times}340.5mm$의 크기로 약 3.6 kg의 무게를 가지며, 탑재체는 방사선에 대하여 인체와 동일한 산란 흡수 특성을 가진 Tissue Equivalent Proportional Counter (TEPC)와 자기장 측정을 위한 Magnetometer (Mag)이다. 위성체는 구조계, 자세제어계, 전력계, 명령 및 데이터처리계, 통신계로 구성되어있다. 구조계는 위성의 뼈대인 Chassis와 Mag deployer로 이루어져있고, 위성의 안정적인 자세유지를 목적으로 Attitude Control System (ACS) Board와 Torque Coil이 자세제어계로 구성된다. 전력의 생산과 공급 및 충전은 태양전지판과 Electrical Power System (EPS), 리튬 배터리로 구성된 전력계에서 이뤄지며, 명령 및 데이터처리계는 On Board Computer (OBC)와 Instrument Interface board (IIB)를 중심으로 서브시스템의 명령체계와 데이터처리를 다룬다. 통신계는 Uplink인 VHF 안테나와 Downlink인 UHF, S-band 안테나로 구성되며 지상과 명령을 송수신한다. SIGMA는 타임인터럽트 기능을 활용한 Flight Software (FSW)로 운용되며 임무에 따른 6가지 모드의 시나리오로 위성을 운용한다. 이에 SIGMA의 개발과 테스트 결과를 소개한다. 본 큐브위성 개발기술을 바탕으로 향후 천문관측용 위성에도 활용할 예정이다.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.475-482
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• 2005

Zn$_{l-x}$Co$_{x}$O (x = 0.05 - 0.20) films were grown on Coming 7059 glass by sol-gel process. A homogeneous and stable Zn$_{l-x}$Co$_{x}$O sol was prepared by dissolving zinc acetate dihydrate (Zn(CH$_{3}$COO)$_{2}$$\cdot$2H$_{2}$O), cobalt acetate tetrahydrate ((CH$_{3}$)$_{2}$$\cdot$CHOH) and aluminium chloride hexahydrate (AlCl$_{3}$ $\cdot$ 6H$_{2}$O) as solute in solution of isopropanol ((CH$_{3}$)$_{2}$$\cdot$CHOH) and monoethanolamine (MEA:H$_{2}$NCH$_{2}$CH$_{2}$OH). The films grown by spin coating method were postheated in air at 650°C for 1 h and annealed in the condition of vacuum (5 $\times$ 10$^{-6}$ Torr) at 300$^{\circ}C$ for 30 min and investigated the nature of c-axis preferred orientation and physical properties with different Co concentrations. Znl_xCOxO thin films with different Co concentrations were well oriented along the c-axis, but especially a highly c-axis oriented Zn$_{l-x}$Co$_{x}$O thin film was grown at 10 at$\%$ Co concentration. The transmittance spectra showed that Zn$_{l-x}$Co$_{x}$O thin films occur typical d-d transitions and sp-d exchange interaction became activated with increasing Co concentration. The electrical resistivity of the films at 10 at$\%$ Co had the lowest value due to the highest c-axis orientation. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetic properties appeared, respectively. The characteristics of the electrical resistivity and room temperature ferromagnetism of Zn$_{l-x}$Co$_{x}$O thin films suggested the possibility for the application to dilute magnetic semiconductors.