• 한국자기학회지
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• 제24권2호
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• pp.51-55
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• 2014

$Fe_3O_4$ 나노입자는 hot-injection 제조법에 의해 제조되었으며 반응물질의 injection time에 변화를 주었다. 격자구조는 x-ray diffraction(XRD) 측정을 통해 Fd-3m 공간군을 갖는 cubic inverse spinel 구조로 분석되었으며, $Fe_3O_4$ 나노입자의 형상은 high-resolution transmission electron microscope(HR-TEM)으로 분석하였다. 반응물질을 각각 0.5분, 60분인 젝션시 각각 7.63 nm, 21.73 nm의 $Fe_3O_4$ 나노입자 사이즈를 얻을 수 있었다. $Fe_3O_4$ 나노입자의 자기적 특성은 다양한 온도에서 vibrating sample magnetometer(VSM)과 M$\ddot{o}$ssbauer spectroscopy로 측정하였으며, hyperthermia 측정을 통해 반응물질의 injection time이 60분일 때 50 kHz의 250 Oe에서 $Fe_3O_4$ 나노입자 파우더의 온도가 약 $120^{\circ}C$임을 관측할 수 있었다.

• 한국자기학회지
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• 제8권6호
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• pp.380-387
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• 1998

본 논문에서는 수소($H_2$)의 주입에 따라(자기적 성질)와 strain (elastic 성질)의 변화가 최대가 될 수 있는 Fe/Zr 다층박막으로 구성된 센서재료를 개발하였다. Sputtering (RF diode) 진공 적층 시스템을 이용하여 srqurntial supttering 빙식으로 변조파장($\lambda$)이 $3{\AA}{$\leq}{\lambda}{$\leq}50{\AA}$이고 $Fe_{80}Zr_{20}$의 성분을 가진 compositionally modulated(CM)된 Fe/Zr 다층박막을 적층 시킨 후 전기분해 방법으로 수소를 주입 시켜 수소에 의해 변화된 자화 및 strain 이 최대가 되는 Fe/Zr 박박을 선택하였다. 박막 재료가 수소화된 자기적 성질의 변화는 자화 및 stain 이 최대가 되는 Fe/Zr 박막을 선태하였다. 박막 재료가 수소화된 후의 자기적 성질의 변화는 히스테리시스 graph와 vibrating sample magnetometer (VSM)를 통해, 그리고 strain 의 변화는 laser heterodyne interferometer (LHI)등으로 분서되어 졌다. 선택된 최적의 센서재료는 single-mode 광섬유를 이용한 Michelson interometer의 sensing arm에 직접 coating 되어 주입된 수소의 양을 간접적으로 측정할 수 잇는 Fiber-optic H2 gas 센서에 응용되엇다. 개발된 센서는 진단하고자 하는 구조물 내의 부식(수소화에 의한) 정도를 손쉽고, 정확하게 감지할 수 있을 것으로 기대 되므로 비파괴 검사(non-destrucive test evaluation; NDE) 응용에 사용될 수 있다.

• 새물리
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• 제68권12호
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• pp.1302-1307
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• 2018

마그네타이트 분말에 대해 Verwey 전이 전후에서의 구조적, 전기적 및 자기적 성질을 고찰하였다. 마그네타이트 시료는 고온열분해법으로 합성한 나노입자를 $800^{\circ}C$, 진공을 뽑는 상태에서 1시간동안 열처리하여 얻었다. 시료의 형태학적, 결정학적 분석은 주사전자현미경(scanning electron microscope, SEM)과 X-선 회절(X-ray diffraction, XRD)을 이용하였으며 시료진동형 자기력계(vibrating sample magnetometer, VSM)와 뫼스바우어 분광법, 비저항 측정 등을 통해 미시적/거시적 자성 및 전기적 특성을 각각 관찰하였다. Verwey 전이점에서 비저항과 자기모멘트의 불연속적 온도의존성을 관측하였으며 자기이방성상수가 $T_V$ 부근에서 약간 감소하는 것이 관찰되었다. 뫼스바우어 스펙트럼은 $T_V$ 전후에서 모두 사면체적 (A) 자리와 팔면체적 (B) 자리에 기인하는 2개의 6선 스펙트럼의 중첩으로 나타났으며 B자리에서 철 이온의 원자가에 따른 흡수선의 구분은 불가능하였다. $T_V$ 를 중심으로 하여 저온영역의 정상스피넬(normal spinel)에서 고온영역의 역스피넬(inverse spinel)의 배위교차(coordination crossover)가 발생하였다.

• Korean Chemical Engineering Research
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• 제54권5호
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• pp.636-647
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• 2016

Magnetite nanoparticles ($Fe_3O_4$ NPs) were synthesized by co-precipitating method under optimized condition. The $Fe_3O_4$ NPs coated with sodium dodecyl sulfate-thenoyltrifluoroacetone ($Fe_3O_4$ NPs-SDS-TTFA) were then exerted as the magnetic solid phase extraction (MSPE) adsorbent for the extraction process prior to introducing to a flame atomic adsorption spectrometry (FAAS). The synthesized $Fe_3O_4$ NPs-SDS-TTFA were applied for the extraction of Pb(II) ions from different water samples. The characterization studies of nanoparticles were performed via scanning electron microscopy-energy dispersive micro-analysis (SEM-EDAX), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) techniques. The substantial parameters affecting the extraction efficiency were surveyed and optimized. A dynamic linear range (DLR) of $10-400{\mu}g\;L^{-1}$ was obtained and the limit of detection (LOD, n=7) and relative standard deviation (RSD%, n= 6, $C=20{\mu}g\;L^{-1}$) were found to be $2.3{\mu}g\;L^{-1}$ and 1.9%, respectively. According to the results, the proposed method successfully applied for the extraction of Pb(II) ions from different environmental water samples and satisfactory results achieved.

• Journal of electromagnetic engineering and science
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• 제16권3호
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• pp.150-158
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• 2016

This paper reports on a study of LiNiZn-ferrite composite as a radiation absorbent material (RAM). The electromagnetic (EM) wave absorbers are composed of an EM wave absorbing material and a polymeric binder. The surface morphology, chemical composition, weight percent of the ferrite composite of the toroid sample, magnetic properties, and return loss are investigated using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and network analyzer. For preparing the absorbing sheet, chlorinated polyethylene (CPE) is used as a polymeric binder. The EM wave absorption properties of the prepared samples were studied at 4 - 8 GHz. We can confirm the effects of the thickness of the samples for absorption properties. An absorption bandwidth of more than a 10-dB return loss shifts toward a lower frequency range along with an increase in the thickness of the absorber.

• Journal of Magnetics
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• 제19권3호
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• pp.205-209
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• 2014

$MnBi_{1-x}Ti_x$ (x = 0, 0.4, 0.7, 1) alloys were prepared by arc-melting, followed by heat treatment. X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were used to measure and investigate the phase structure and magnetic properties. The temperature dependent magnetization curves indicate that the phase transitions between LTP and HTP MnBi occur with heating or cooling in $MnBi_{1-x}Ti_x$ ($x{\leq}0.7$) samples. However, MnTi samples are in $Mn_2Ti$ single-phase, with very low magnetic properties. Furthermore, the coercivity exhibits a positive temperature coefficient. The results show that the optimal content of Ti for the coercivity of $MnBi_{1-x}Ti_x$ alloy is x = 0.4. For MnBi sample, the coercivity reaches a maximum value of 1.13 T at 550 K. However, the remanence and energy product show apparent decrease with the addition of Ti in $MnBi_{1-x}Ti_x$ alloys.

• 한국재료학회지
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• 제30권2호
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• pp.74-80
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• 2020

Synthesis of composite powders for the Fe₂O₃-Zn system by mechanical alloying (MA) has been investigated at room temperature. Optimal milling and heat treatment conditions to obtain soft magnetic composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that α-Fe/ZnO composite powders in which ZnO is dispersed in α-Fe matrix can be obtained by MA of Fe₂O₃ with Zn for 4 hours. The change in magnetization and coercivity also reflects the details of the solid-state reduction process of hematite by pure metal of Zn during MA. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at 900 ~ 1,000 ℃ under 60 MPa. Shrinkage change after SPS of sample MA'ed for 5 hrs was significant above 300 ℃ and gradually increased with increasing temperature up to 800 ℃. X-ray diffraction results show that the average grain size of α-Fe in the α-Fe/ZnO composite sintered at 900 ℃ is in the range of 110 nm.

• 한국재료학회지
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• 제34권3호
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• pp.138-143
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• 2024

Ni-CNT nanocomposites were synthesized via the electrical explosion of wire (EEW) in acetone and deionized (DI) water liquid conditions with different CNT compositions. The change in the shape and properties of the Ni-CNT nanopowders were determined based on the type of fluids and CNT compositions. In every case, the Ni nanopowder had a spherical shape and the CNT powder had a tube shape. However, the Ni-CNT nanopowders obtained in DI water exhibited irregular shapes due to the oxidation of Ni. Phase analysis also revealed the existence of nickel oxide when using DI water, as well as some unknown peaks with acetone, which may form due to the metastable phase of Ni. Magnetic properties were investigated using a Vibrating Sample Magnetometer (VSM) for all cases. Nanopowders prepared in DI water conditions had better magnetic properties than those in acetone, as evidenced by the simultaneous formation of super paramagnetic NiO peaks and ferromagnetic Ni peaks. The DI water (Ni:CNT = 1:0.3) sample revealed better magnetic results than the DI water (Ni-CNT = 1:0.5) because it had less CNT contents.

• 한국재료학회지
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• 제25권12호
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• pp.703-707
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• 2015

In this study, we investigated the effect of annealing conditions on the ferromagnetic resonance(FMR) of yttrium iron garnet ($Y_3Fe_5O_{12}$, YIG) thin film prepared on gadolinium gallium garnet ($Gd_3Ga_5O_{12}$, GGG) substrate. The YIG thin films were grown by rf magnetron sputtering at room temperature and were annealed at various temperatures from 700 to $1000^{\circ}C$. FMR characteristics of the YIG thin films were investigated with a coplanar waveguide FMR measurement system in a frequency range from 5 to 20 GHz. X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) were used to characterize the phase formation, crystal structure and composition of the YIG thin films. Field dependent magnetization curves at room temperature were obtained by using a vibrating sample magnetometer(VSM). The FMR measurements revealed that the resonance magnetic field was highly dependent on the annealing condition: the lowest FMR linewidth can be observed for the $800^{\circ}C$ annealed sample, which agrees with the VSM results. We also found that the Fe and O composition changes during the annealing process play important roles in the observed magnetic properties.

• 한국자기학회지
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• 제9권1호
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• pp.29-34
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• 1999

자성 garnet Y2.5La0.5Fe5O12의 분말을 ethylene glycol을 용매로 이용한 sol-gel방식으로 합성하였다. 시료의 결정학적 및 자기적 성질을 x선 회절기(XRD), 진동시료 자화기(VSM), 그리고 Mossbauer 분광기를 이용하여 연구하였다. 분말의 경우 100$0^{\circ}C$에서 단일상의 garnet결정을 얻었으며 결정구조는 cubic구조이며 격자상수는 12.415$\AA$이었다. Mossbauer spectrum은 13K부터 700K까지 측정하였으며 Fe는 모두 +3가 상태로 16(a)와 24(d)site에 존재함을 확인하였다. spin wave 상수는 B3/2=0.32$\pm$0.05, C5/2=0.18$\pm$0.05였으며, Debye 온도는 24(d)site인 경우 382K 그리고 16(a) site인 경우 246K였다. VSM 실험으로부터 상온에서 포화 자화값(Ms)은 25emu/g이었다.