• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.21-28
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• 2003

M-type hexagonal BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$ (0$\leq$x$\leq$1.0) ferrite powders prepared by a sol-gel method. The crystallographic and magnetic properties were characterized with a x-ray diffraction (XRD), thermogravimetry (TG), differential thermal analysis (DIA), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. The result of XRD measurements show that the a and c lattice parameters increase with increasing x from $\alpha$=5.882 and c=23.215 $\AA$ for $\chi$=0.0, to $\alpha$=5.895 and c=23.295 $\AA$ for $\chi$=1.0. From the Mossbauer results, the $Co^{2+}$- $Ti^{4+}$ site occupancies have been affected the changes in the magnetization and in the coercivity. The Curie temperature linearly decreases with increasing $Co^{2+}$- $Ti^{4+}$ concentration x.

• 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 Magnetics Society
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• v.9 no.4
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• pp.190-195
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• 1999

The crystallographic and magnetic properties of the system of $Fe_{1-x}Co_x$(x=0.2 and 0.4) prepared by microwave arc-melting with the maximum power of 3.5 kW and a iron-foil with thickness of 25 ${\mu}{\textrm}{m}$ have been studied by the methods of X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in three different ways: First, pellet form pressed under the pressure of 9,000 N/$\textrm{cm}^2$. Second, the sheet cold rolled. Third, thin sheet treated with the temperature of 90$0^{\circ}C$. The X-ray diffraction pattern of the sample prepared by the first method shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The iron-foil has the coercivity of 43 Oe and the initial slope of magnetization of 0.328 emu/gOe. The coervicity and magnetization of the sample prepared by the second method increased as the Co content increased. But the initial slop of the magnetization decreased as the Co content increased. This means that the displacement of domain wall is suppressed by the increases of coercivity as the Co content increased. The saturation magnetization of the samples made by the third method increased. On the other hand, the coercivity of these samples decreased. The increase of saturation magnetization of the samples seems to be related to the changes in X-ray intensity after heat treatment. Also some magnetic parameters of the samples were calculated by using a simple model and compared with other values.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.1-6
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• 2002

Al$\^$3+/ substituted garnet Y$_3$Fe$\_$5-x/Al$\_$x/O$\_$12/ (x=0.0, 0.25, 0.5, 0.75, 1.0) was fabricated by sol-gel method. The crystallographic and magnetic properties of Y$_3$Fe$\_$5-x/Al$\_$x/O$\_$12/ have been studied with Mossbauer spectroscopy, x-ray diffraction (XRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA), and vibrating samples magnetometer (VSM). The crystal structure of Y$_3$Fe$\_$5/O$\_$12/ is found to be a cubic with the lattice constant a$\_$0/= 12.381$\pm$0.005 $\AA$. The lattice constants a$\_$0/ decreases linearly from 12.381 to 12.304 A as the Al concentration (x) increases from x=0.0 to 1.0. Mossbauer spectra of measured at Y$_3$Fe$\_$5-x/A1$\_$x/O$\_$12/ various absorber temperatures of 13 to 600 K. Mossbauer spectrum for x = 0.0 is consist of well resolved two sets of six line patterns. While with increasing Al concentration outer sextet patters, which is originating from octahedral sites, broadens widely. These phenomena are interpreted in terms of random probability distributions of Fe$\^$3+/ and Al$\^$3+/ in tetrahedral site.

• 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$_{C}$).