• 한국세라믹학회지
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• 제39권12호
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• pp.1119-1123
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• 2002

Nanostructured spinel NiZn ferrites were prepared by the sol-gel method from metal nitrate raw materials. Analyses by X-ray diffraction and scanning electron microscopy showed the average particle size of NiZn ferrite was under 50 nm. The single phase of NiZn ferrites was obtained by firing at 250${\circ}C$, resulting in nanoparticles exhibiting normal ferrimagnetic behavior. The nanostructured $Ni_{1-X}Zn_XFe_2O_4$ (x=0.0∼1.0) were found to have the cubic spinel structure of which the lattice constants ${\alpha}_2$ increases linearly from 8.339 to 8.427 ${\AA}$ with increasing Zn content x, following Vegard's law, approximately. The saturation magnetization $M_s$ was 48 emu/g for x=0.4 and decreased to 8.0 emu/g for higher Zn contents suggesting the typical ferrimagnetism in mixed spinel ferrites. Pure NiZn ferrite phase substituted by Cu was observed before using the additive but hematite phase was partially appeared at $Ni_{0.2}Zn_{0.2}Cu_{0.6}Fe_2O_4$. On the other hand, the hematite phase in this NiZn Cu ferrite was disappeared after using the additive of acethyl aceton with small amount. The saturation magnetization Ms of $Ni_{0.2}Zn_{0.8-y}Cu_yFe_2O_4$(y=0.2∼0.6) as measured was about 51 emu/g at 77K and 19 emu/g at room temperature, respectively.

• 한국자기학회지
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• 제20권6호
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• pp.207-211
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• 2010

우리는 증기전달법(vapor transport method)으로 성장된 $Cr_5S_6$ 단결정의 자기저항 효과를 연구하였다. 상온에서의 X-선 회절 (X-ray diffraction) 연구는 삼방구조(trigonal structure)를 가지는 단결정의 상 형성을 보여주었다. 5 K~400 K 온도영역에서 온도의 함수로 자기장(0.1 T, 5 T)을 걸어주면서 자화를 측정하였다. 자화의 온도의존성 결과로부터 $Cr_5S_6$의 두 가지 상태변화를 확인 할 수 있었다. 첫 번째는 150 K 근처에서 반강자성에서 준강자성으로의 전이가 일어나고, 두 번째는 준강자성에서 상자성으로의 전이가 300 K 근처에서 일어난다. 0 T와 5 T의 자기장에서 측정한 온도에 따른 저항의 변화는 150 K 근처에서 반강자성-준강자성 전이를 보여주면서 금속성을 보여주었다. 자기장의 변화에 따른 자화의 변화를 고정된 온도(100 K, 150 K, 200 K, 그리고 300 K)에서 측정하였다. 200 K과 300 K에서는 M-H 이력 현상을 잘 보여주는 반면에, 100 K과 150 K에서는 이력 현상을 보여주지 않았다. 150 K, 즉 반강자성 전이온도에서 $Cr_5S_6$는 5 T의 자기장 하에서 약 -2%의 음의 자기저항(magnetoresistance)이 관찰되었다.

• 한국세라믹학회지
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• 제39권1호
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• pp.12-15
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• 2002

Ultrafine cadmium ferrite particles have been investigated by X-ray diffractometry, transmission electron microscopy and SQUID magnetometry. All peaks of X-ray diffraction patterns are broad, but correspond to a cubic spinel structure with the lattice constant of 8.65 $\AA$. The average particle size determined by TEM is 9.7 nm and the size distribution of particles is not normal, but lognormal. The maximal magnetization measured at 5 K was 17.7 emu/g. The experimental data show a transi-tion from a disorder ferrimagnetic phase to a spin-glass phase (i.e. reentrant behavior) with a freezing temperature (T$\_$f/) of 30 K. Superparamagnetic behavior of the particles is confirmed by the coincidence of the plots of M vs. H/T for 100 and 300 K.

• Journal of Magnetics
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• 제5권4호
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• pp.111-115
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• 2000

Ultrafine $Co_{0.9}Mn_{0.1}Fe_2O_4$ powders have been fabricated by a sol-gel method. Structural and magnetic properties of the powders were investigated by x-ray diffractometry, transmission electron microscopy (TEM), Mossbauer spectroscopy, and vibrating sample magnetometry (VSM). Co-Mn ferrite powders that were fired at and above 773 K contained only a single spinel phase and behaved ferrimagnetically. Powders fired at 673 and 723 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. The magnetic behavior of Co-Mn ferrite powders fired at and above 873 K showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum saturation magnetization and coercivity of Co-Mn ferrite powders were 66.7 emu/g and 1523 Oe, respectively, Mossbauer spectra of the powder fired at 923 K were taken at various temperatures ranging from 13 to 850 K. The iron ions.at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Nel temperature $T_N$ was found to be 850 $\pm$ 2 K. Debye temperatures far A and B sites were found to be $\Theta_A = 757 \pm$5K and $Theta_B = 282 \pm$5 K, respectively.

• Journal of Magnetics
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• 제18권1호
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• pp.26-29
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• 2013

$Mn_xFe_{3-x}O_4$ powders have been fabricated by using sol-gel methods; their crystallographic and magnetic properties were investigated by using X-ray diffraction, scanning electron microscopy, M$\ddot{o}$ssbauer spectroscopy, and vibrating sample magnetometer. The $Mn_xFe_{3-x}O_4$ ferrite powders annealed at $500^{\circ}C$ had a single spinel structure regardless of the $Mn^{2+}$-doping amount and their lattice constants became larger as the $Mn^{2+}$ concentration was increased. Their Mossbauer spectra measured at room temperature were fitted with 2 Zeeman sextets due to the tetrahedral and octahedral sites of Fe ions, which made them ferrimagnetic. The magnetic behavior of $Mn_xFe_{3-x}O_4$ powders showed that the $Mn^{2+}$-doping amount made their saturation magnetization increase, but there were no severe effects on their coercivities. The saturation magnetization of the $Mn_xFe_{3-x}O_4$ powder varied from 38 emu/g to 70.0 emu/g and their minimum coercivity was 111.1 Oe.

• 한국자기학회지
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• 제13권3호
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• pp.97-102
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• 2003

고집적 TMR소자의 프리층에 적용될 수 있는 인위적페리층(synthetic ferrimagnetic layer : SyFL)인 NiFe/Ru/NiFe박막을 만들고, 결정에너지, 지만에너지, 교환에너지를 고려한 총에너지로부터 평형상태에서의 관계식에서 Ru두께에 따른 보자력( $H_{c}$)변화와, 스핀플로핑자계( $H_{sf}$ ), 포화자계( $H_{s}$)에 대해 알아보았다. Ta(50$\AA$)/NiFe(50$\AA$)Ru(4~20$\AA$)/NiFe(30$\AA$)/Ta(50$\AA$) 구조를 ICP (inductively coupled plasma)형 헬리콘스퍼터로 제작하고, 주어진 Ru두께에서의 시편을 SQUID로 $\pm$15kOe까지 분석하여 M-H루프를 측정하였다. 에너지를 고려한 평형상태 예측은 실험과 잘 일치하였으며, 이방성에너지 $K_{u}$= 1000erg/㎤, 교환에너지 $J_{ex}$= 0.7erg/$\textrm{cm}^2$까지 조절이 가능하였다. 상온에서 $H_{c}$를 10 Oe이하로 만드는 것이 가능하였고, 공업적으로 의미있는 $H_{s}$, $H_{sf}$ 의 범위를 Ru두께 4~10 $\AA$에서 선택이 가능하였다. 또한 50 $\AA$이하의 얇은 NiFe박막에서 자기탄성계수는 0이 아닌 (+)로 작용할 수 있다는 점과 NiFe/Ru 계면 조도를 간접적으로 예상하는 것이 가능하였다.

• Journal of Magnetics
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• 제10권1호
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• pp.5-9
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• 2005

Nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ is fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with XRD, SEM, Mossbauer spectroscopy, and VSM. $Ni_{0.9}Zn_{0.1}Fe_2O_4$ powders annealed at $300{^{\circ}C}$ have a spinel structure and behaved superparamagnetically. The estimated size of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 10 nm. The hyperfine fields at 13 K for the A and B patterns are found to be 533 and 507 kOe, respectively. The ZFC curves are rounded at the blocking temperature ($T_B$)and show a paramagnetic-like behavior above $T_B$. $T_B$ of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 250 K. Nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at 400 and $500{^{\circ}C}$ have a typical spinel structure and is ferrimagnetic in nature. The isomer shifts indicate that the iron ions were ferric at the tetrahedral (A) and the octahedral (B). The saturation magnetization of nanoparticles $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at 400 and $500{^{\circ}C}$ are 40 and 43 emu/g, respectively. The magnetic anisotropy constant of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ annealed at $300{^{\circ}C}$ were calculated to be 1.6 ${\times}$ $10^6$ ergs/$cm^3$.

• 한국자기학회지
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• 제25권5호
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• pp.144-148
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• 2015

스피넬 결정구조를 지니는 $CoMn_2O_4$ 박막을 증착하였으며 이들 박막의 물리적 특성을 후열처리 이전과 이후로 비교 조사하였다. 증착온도인 $720^{\circ}C$보다 낮은 $700^{\circ}C$에서의 후열처리 과정 이후, 열처리 이전의 불분명했던 tetragonal 결정구조가 분명하여졌으며 이는 곧 표면상태의 변화로도 관측되었다. 자성특성의 경우 약 100 K에서 다결정 형태의 벌크에서는 측정할 수 없었던 상전이가 관측되었다. 상전이온도 이상의 온도에서는 전형적인 강자성 특성을 보이는 반면 상전이온도 이하에서는 페리자성 특성을 보였다. 특히 열처리 이후에는 페리자성 특성은 매우 뚜렷하여졌다. 이와 같은 결과는 후열처리과정이 $CoMn_2O_4$ 박막의 물리적 특성을 결정짓는데 필수적임을 의미한다.

• Journal of Magnetics
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• 제21권3호
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• pp.308-314
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• 2016

Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, $MnFe_2O_4$, $Mn_{0.8}Co_{0.2}Fe_2O_4$, $Mn_{0.8}Zn_{0.2}Fe_2O_4$ and $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The $MnFe_2O_4$ ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The $M{\ddot{o}}ssbauer$ spectrum of the $MnFe_2O_4$ ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the $M{\ddot{o}}ssbauer$ spectra of the $MnFe_2O_4$, $Mn_{0.8}Co_{0.2}Fe_2O_4$, and $Mn_{0.8}Zn_{0.2}Fe_2O_4$ ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. However, the $M{\ddot{o}}ssbauer$ spectrum of the $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$ ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the $M{\ddot{o}}ssbauer$ spectra could be used to determine the cation distribution equation, and we also explained the variation in the $M{\ddot{o}}ssbauer$ parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure $MnFe_2O_4$, the saturation magnetizations and coercivities were larger in $Mn_{0.8}Co_{0.2}Fe_2O_4$ and smaller in $Mn_{0.8}Zn_{0.2}Fe_2O_4$, and $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.

• Journal of Magnetics
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• 제11권4호
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• pp.195-207
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• 2006

The recently published and new results on design and fabrication of magnetophotonic crystals of different dimensionality are surveyed. Coupling of polarized light to 3D photonic crystals based on synthetic opals was studied in the case of low dielectric contrast. Transmissivity of opals was demonstrated to strongly depend on the propagation direction of light and its polarization. It was shown that in a vicinity of the frequency of a single Bragg resonance in a 3D photonic crystal the incident linearly polarized light excites inside the crystal the TE- and TM-eigen modes which passing through the crystal is influenced by Brags diffraction of electromagnetic field from different (hkl) sets of crystallographic planes. We also measured the faraday effect of opals immersed in a magneto-optically active liquid. It was shown that the behavior of the faraday rotation spectrum of the system of the opal sample and magneto-optically active liquid directly interrelates with transmittance anisotropy of the opal sample. The photonic band structure, transmittance and Faraday rotation of the light in three-dimensional magnetophotonic crystals of simple cubic and face centered cubic lattices formed from magneto-optically active spheres where studied by the layer Korringa-Kohn-Rostoker method. We found that a photonic band structure is most significantly altered by the magneto-optical activity of spheres for the high-symmetry directions where the degeneracies between TE and TM polarized modes for the corresponding non-magnetic photonic crystals exist. The significant enhancement of the Faraday rotation appears for these directions in the proximity of the band edges, because of the slowing down of the light. New approaches for one-dimensional magnetophotonic crystals fabrication optimized for the magneto-optical Faraday effect enhancement are proposed and realized. One-dimensional magnetophotonic crystals utilizing the second and the third photonic band gaps optimized for the Faraday effect enhancement have been successfully fabricated. Additionally, magnetophotonic crystals consist of a stack of ferrimagnetic Bi-substituted yttrium-iron garnet layers alternated with dielectric silicon oxide layers of the same optical thickness. High refractive index difference provides the strong spatial localization of the electromagnetic field with the wavelength corresponding to the long-wavelength edge of the photonic band gap.