• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.66-70
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• 2006

Magnetite nanoparticles, which have been extensively used in many fields, were encapsulated with a natural polymer, chitosan, to improve their biocompatibility. We have synthesized magnetite $(Fe_3C_4)$ nanoparticles using chemical coprecipitation technique with sodium oleate as surfactant. Nanoparticle size can be varied from 1.2 to 7.4nm 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. High magnetic property chitosan-microsphere particles were prepared from oleate-coated magnetite suspension using spray method. The surftce, and tile morphology of the magnetic chitosan microsphere particles were characterized using optical microscope and scanning electron microscope. Magnetic hysteresis measurement were performed using a superconducting quantum interference device (SQUID) magnetometer at room temperature to investigate the magnetic properties of the chitosan microspheres including magnetite nanoparticles. The SQUID measurements revealed superparamagnetism of nanoparticles.

• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.163-167
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• 2006

Ultrasonic irradiation in a solution during the chemical reaction may accelerate the rate of the reaction and the crystallization at low temperature. We have synthesized nanometer sized magnetite particles using coprecipitation method, sonochemical method without surfactant, and sonochemical method with surfactant, in order to investigate the effect of ultrasonic irradiation and surfactant on the coprecipitates of metal ions. The size of the magnetite nanoparticles prepared by coprecipitation method, and sonochemical method without surfactant showed broad distributions. But we got uniform nanoparticles using a sonochemical method with oleic acid. The average size of the particles can be controlled by the ratio $R=[H_2O]/[surfactant]$. The size of the magnetite nanoparticles prepared by this method showed narrow distributions. We have characterized the nanoparticles using an X-ray diffraction (XRD), a superconducting quantum interference device (SQUID), and atomic force microscope (AFM). The size and distribution of the magnetite nanoparticles were measured by dynamic light scattering (DLS) method.

• Journal of the Korean Magnetics Society
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• v.13 no.5
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• pp.211-215
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• 2003

We fabricated the synthetic ferrimagnetic layers (SyFL) of permalloy/X (X=Ru, V)/permalloy by varying the X thickness, and investigated the changes of coercivity (H$\sub$c/), spin flopping field (H$\sub$sf/), and saturation magnetization field (H$\sub$s/) with a superconducting quantum interference device (SQUID). We also observed the microstructure with a cross sectional transmission electron microscope (TEM). Permalloy SyFL had less than 10 Oe coercivity, and H$\sub$sf/ and H$\sub$s/ could be tuned by varying ruthenium and vanadium layer thickness. The comparatively small exchange coupling in permalloy-V SyFL was caused by the intermixing of permalloy and vanadium decreasing the effective exchange coupling thickness.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2408-2412
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• 2013

We demonstrate herein the synthesis and modification of magnetic nanoparticles and its use in the immobilization of the lipase. Magnetic $Fe_3O_4$ nanoparticles (MNPs) were prepared by simple co-precipitation method in aqueous medium and then subsequently modified with tetraethyl orthosilicate (TEOS) and 3-aminopropyl triethylenesilane (APTES). Silanization magnetic nanoparticles (SMNP) and amino magnetic nanomicrosphere (AMNP) were synthesized successfully. The morphology, structure, magnetic property and chemical composition of the synthetic MNP and its derivatives were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) analysis, X-ray diffraction, superconducting quantum interference device (SQUID) and thermogravimetric analyses (TGA). All of these three nanoparticles exhibited good crystallization performance, apparent superparamagnetism, and the saturation magnetization of MNP, SMNP, AMNP were 47.9 emu/g, 33.0 emu/g and 19.5 emu/g, respectively. The amino content was 5.66%. The AMNP was used to immobilize lipase, and the maximum adsorption capacity of the protein was 26.3 mg/g. The maximum maintained activity (88 percent) was achieved while the amount of immobilized lipase was 23.7 mg $g^{-1}$. Immobilization of enzyme on the magnetic nanoparticles can facilitate the isolation of reaction products from reaction mixture and thus lowers the cost of enzyme application.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.11
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• pp.2137-2142
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• 2016

The electrical current generated by heart creates not only electric potential but also a magnetic field. In this study, the signals obtained magnetocardiogram(MCG) using 61 channel superconducting quantum interference device(SQUID) system, and the clinical significance of various feature parameters has been developed MCG. Neural network algorithm was used to perform the classification of ischemic heart disease. The MCG signal was obtained to facilitate the extraction of parameters through a process of pre-processing. The data used to research the normal group 10 and ischemic heart disease group 10 with visible signs of stable angina patients. The available clinical indicators were extracted by characteristic point, characteristic interval parameter, and amplitude ratio parameter. The extracted parameters are determined to analysis the significance and clinical parameters were defined. It is possible to classify ischemic heart disease using the MCG feature parameters as a neural network input.

• Journal of Biomedical Engineering Research
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• v.27 no.4
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• pp.154-163
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• 2006

A 64-channel magnetocardiogram (MCG) system using low-noise superconducting quantum interference device (SQUID) planar gradiometers was developed for the measurements of cardiac magnetic fields generated by the heart electric activity. Owing to high flux-to-voltage transfers of double relaxation oscillation SQUID (DROS) sensors, the flux-locked loop electronics for SQUID operation could be made simpler than that of conventional DC SQUIDs, and the SQUID control was done automatically through a fiber-optic cable. The pickup coils are first-order planar gradiometers with a baseline of 4 em. The insert has 64 planar gradiometers as the sensing channels and were arranged to measure MCG field components tangential to the chest surface. When the 64-channel insert was in operation everyday, the average boil-off rate of the dewar was 3.6 Lid. The noise spectrum of the SQUID planar gradiometer system was about 5 fT$_{rms}$/$\checkmark$Hz at 100 Hz, operated inside a moderately shielded room. The MCG measurements were done at a sampling rate of 500 Hz or 1 kHz, and realtime display of MCG traces and heart rate were displayed. After the acquisition, magnetic field mapping and current mapping could be done. From the magnetic and current information, parameters for the diagnosis of myocardial ischemia were evaluated to be compared with other diagnostic methods.

• Journal of the Korean Magnetics Society
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• v.9 no.3
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• pp.143-148
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• 1999

Magnetic properties and crystallographic properties of $Cu_{1-x}Ge_{1-y}Fe_{x+y}O_3$ system were studied by using x-ray diffraction, superconducting quantum interference device (SQUID) and Mossbauer spectroscopy. All the samples have orthorhombic structure and the lattice constants some decreased as the substituted iron contents increasing. The spin-Peierls (SP) transition temperature of our samples are about 12.5 K and these temperatures lowered as increasing substituted iron contents. The Mossbauer spectra consisted with two Zeeman sextets and one doublet due to $Fe^{3+}$ ions. The jump up of magnetic hyperfine field of 2nd Zeeman sextet and the increasing of the values of quadrapole splitting and isomer shift of doublet below SP transition temperature could be interpreted with the variation of the superexchange interaction, the symmetry of lattice sites and the covalency of bonds due to the atomic displacements.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1555-1560
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• 2018

$AlFe_2B_2$ produced by using a conventional arc melter has a ferromagnetic material with a Curie temperature ($T_C$) of around 300 K, but the arc-melt generates paramagnetic $Al_{13}Fe_4$ impurities during the synthesis of $AlFe_2B_2$. Impurities are brought to cause a decrease in magnetocaloric effects (MCEs). To investigate the effects of $Al_{13}Fe_4$ impurities on MCEs, we prepared and compared ascast and acid-treated samples, where the acid treatment was performed to remove the $Al_{13}Fe_4$ impurities. For the structural analysis, powder X-ray diffraction was carried out, and the measured data were subjected to a Rietveld refinement. The presence of $Al_{13}Fe_4$ impurities in the as-cast sample was observed in the phase analysis measurements. Magnetic properties were investigated by using Superconducting Quantum Interference Device (SQUID) measurements for the as-cast and the acid-treated $AlFe_2B_2$ samples. From isothermal magnetization measurements, Arrott plots were obtained showing that the transition of $AlFe_2B_2$ has a second-order magnetic phase transition (SOMT). The $T_C$ and the saturation magnetization increased for the acid-treated sample due to removal of the paramagnetic impurities. As a consequence, the magnetic entropy change ($-{\Delta}S$) increased in the pure $AlFe_2B_2$ samples, but the full width at half maximum in the plot of $-{\Delta}S$ vs. T decreased due to the absence of impurities.

• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.155-159
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• 2003

We report on the annealing effect and ferromagnetic characteristics of Zn$_{0.7}$Mn$_{0.3}$O film prepared by sol-gel method on the silicon (100) substrate using field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and superconducting quantum interference device (SQUID) magnetometry. Magnetic measurements show thatZn$_{0.7}$Mn$_{0.3}$O films exhibit ferromagnetism at 5 K revealing the coercive field of ∼110 Oe for as grown sample and 360, 1035 Oe for samples annealed at 700, 800 $^{\circ}C$, respectively. Our experimental evidence suggests that ferromagnetic precipitates of a manganese oxide may be responsible for the observed ferromagnetic behaviors of the film.he film.

• Journal of the Korean Magnetics Society
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• v.18 no.2
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• pp.49-53
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• 2008

Magnetic and crystallographic properties of patterned media fabricated by nanoimprint lithography and Co-Pt electroplating were studied. Thin films of Ru(20 nm)/Ta(5 nm)/$SiO_2$(100 nm) were deposited on Si(100) wafer and then 25 nm hole pattern was fabricated by nanoimprint lithography on substrate. The electroplated Co-Pt nano-dots have the diameter of 35 nm and the height of 27 nm. Magnetic dot patterns of Co-Pt alloy were created using electroplated Co-Pt alloy and then their properties were measured by MFM, SQUID, SEM, TEM and AFM. We observed single domain with perendicular anisotropy for each dot and achieved optimum coercivity of 2900 Oe. These results mean that patterned media fabricated by nanoimprint lithography and electroplating have good properties in view of extending superparamagnetic limit while satisfying the writability requirements with the present write heads.