• Journal of the Korean Chemical Society
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• v.41 no.5
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• pp.271-276
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• 1997

• New Physics: Sae Mulli
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• v.68 no.12
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• pp.1302-1307
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• 2018

The crystallographic, electrical and magnetic behaviors of magnetite powder in the vicinity of its Verwey transition were investigated in this study. Magnetite was prepared by synthesizing a nanoparticle precursor and then annealing it at $800^{\circ}C$ for 1 h under a dynamic vacuum. Crystallographic and morphology analyses were done by using scanning electron microscope (SEM) and X-ray diffraction (XRD). The electrical and the magnetic properties were examined by using $M{\ddot{o}}ssbauer$ spectroscopy, vibrating sample magnetometer (VSM) and resistivity measurement. Both the magnetic moment and the resistivity showed discontinuous changes at the Verwey transition temperature ($T_V$). The temperature dependence of magnetic anisotropy constant showed a monotonic decrease with increasing temperature, with slight dip near $T_V$. $M{\ddot{o}}ssbauer$ spectra showed the superposition of two sextets, one from the tetrahedral (A) and the other from the octahedral (B) sites. The results revealed that identical charge states existed in the B site at temperatures both above and below $T_V$. A coordination crossover resulted in a transition from an inverse to a normal spinel at or close to $T_V$.

• Archives of Pharmacal Research
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• v.8 no.2
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• pp.91-98
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• 1985

Dependence of the flow behavior of aqueous suspension of Young-Il bentonite on the concentration and the type of electrolytes was studied. Viscosity measurements were made was Rion Viscotester, using No. 3 rotor at 62.5 R. P. M. at 25.deg.C. As electrolyte concentration increased, the apparent viscosity was observed to increase. Changes in viscosity were in general agreement with predicted results based on the Hofmeister sequence and the Schulze-Hardy rule. The observed electrolyte effect on the apparent viscosity was discussed in terms of the Verwey-Overbeek theory.

• Journal of the Korean Magnetic Resonance Society
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• v.22 no.4
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• pp.101-106
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• 2018

Magnetite is the oldest magnet material known to mankind. It is getting attention again from solid state physics researchers now a days because it is one of the most strongly correlated electron systems. Spin, charge, and orbital orders are interplaying with lattice and involved in the Verwey transition where magnetization, conductivity, and structure changes suddenly. The peculiar ordering states above and below the transition temperature mainly originate from the coexistence of $Fe^{2+}$ and $Fe^{3+}$ ions in the B site of the inverse spinel structure. In particular, the state of the charge and orbital order was the oldest and most intriguing problem. NMR has made significant contribution to the investigation of this question. A. Abragam stated that there is no doubt that NMR is a very powerful tool for the study of ferromagnetic and antiferromagnetic materials. In this mini-review, a short history of NMR investigation of magnetite is presented, providing a support to Abragam's claim.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.60-60
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• 2011

Giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), and magnetic random-access memory (MRAM) are currently active research areas in spintronics. The high magnetoresistance and the high spin polarization (P) of electrons in the ferromagnetic electrodes of tunnel junction or intermediate layers are required. Magnetite, Fe3O4, is predicted to possess as half-metallic nature, P ~ 100% spin polarization, and has a high Curie temperature (TC~850 K). Experiments demonstrated that the P~($80{\pm}5$)%, ~($60{\pm}5$)%, and ~40-55% for epitaxial (111), (110) and (001)-oriented Fe3O4 thin films, respectively. Epitaxial Fe3O4 films may enable us to investigate the effects of half metals on the spin transport without grain-boundary scattering.In addition, it has been reported that the Verwey transition (TV, a first order metal-insulator transition) of 120 K in bulk Fe3O4 is strongly affected by many parameters such as stoichiometry and stress, etc. Here we report that the growth modes, magnetism and transport properties of Fe3O4 thin films were strongly dependent on the oxygen pressure during film growth. The average roughness decreases from 1.021 to 0.263 nm for the oxygen pressure increase from $2.3{\times}10-7$ to $8.2{\times}10^{-6}$ Torr, respectively. The 120 K Verwey transition in Fe3O4 was disappeared for the sample grown under high oxygen pressure.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.538-543
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• 2014

It is investigated that that the physical properties of Glutathione layer formed on gold surfaces may make an effect on the distribution of either gold particle adsorbed to the $ZrO_2$ surface or vice versa with the adjustment of the electrostatic interactions. For the investigation, the atomic force microscope (AFM) was used to measure the surface forces between the surfaces as a function of the salt concentration and pH value. The forces were quantitatively analyzed with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to estimate the surface potential and charge density of the surfaces for each condition of salt concentration and pH value. The estimated-value dependence on the salt concentration was described with the law of mass action, and the pH dependence was explained with the ionizable groups on the surface. The salt concentration dependence of the surface properties, found from the measurement at pH 4 and 8, was consistent with the prediction from the law. It was found that the Glutathione layer had higher values for the surface charge densities and potentials than the zirconium dioxide surfaces at pH 4 and 8, which may be attributed to the ionized-functional-groups of the Glutathione layer.

• Journal of the Korean Magnetics Society
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• v.25 no.2
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• pp.43-46
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• 2015

$Si(100){\backslash}200nm$ $SiO_2{\backslash}5nm$ $Ta{\backslash}5nm$ $MgO{\backslash}35nm$ $Fe_3O_4$ multi-layers were prepared by using RF-sputtering and ultra-high vacuum molecular beam epitaxy (UHV-MBE) techniques. After post-annealing the multi-layers at $500^{\circ}C$ for 1 hour under the high vacuum of ${\sim}1{\times}10^{-6}Torr$, we observed ferromagnetic properties at room temperature as well as the Verwey transition which is the typical features of magnetite crystals formed. We have carried out a comparative study of the effect of Ta buffered layer on the crystallinity and magnetic properties of $Fe_3O_4$ thin films prepared under different growth and annealing conditions.

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.607-612
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• 2014

The physical properties of mercaptoundecanoic-acid layer formed on gold surfaces, which may affect the distribution of either gold particles adsorbed to the zirconium dioxide surface or vice versa, were investigated. To conduct this investigation, the surface forces were measured between the surfaces with respect to the salt concentration and pH value using atomic force microscope (AFM). The forces were quantitatively converted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to the surface potential and charge density of surfaces. The converted-value dependence on the salt concentration and pH was described with the law of mass action, and the dependence was consistent with the theoretical prediction. It was found that the mercaptoundecanoic-acid layer had higher values for the surface charge densities and potentials than the $ZrO_2$ surfaces, which may be attributed to the ionized-functional-groups of the mercaptoundecanoic-acid layer.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.379-384
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• 2012

It is investigated that that the physical properties of Glutathione layer formed on gold surfaces may make an effect on the distribution of either gold particle adsorbed to the $TiO_2$ surface or vice versa with the adjustment of the electrostatic interactions. For the investigation, the atomic force microscope (AFM) was used to measure the surface forces between the surfaces as a function of the salt concentration and pH value. With the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the forces were quantitatively analyzed to acquire the surface potential and charge density of the surfaces for each salt concentration and each pH value. The surface potential and charge density dependence on the salt concentration was described with the law of mass action, and the pH dependence was explained with the ionizable groups on the surface. The salt concentration dependence of the surface properties, found from the measurement at pH 8 and 11, was consistent with the prediction from the law. It was found that the Glutathione layer had higher values for the surface charge densities and potentials than the titanium dioxide surfaces at pH 8 and 11, which may be attributed to the ionized-functional-groups of the Glutathione layer.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.625-630
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• 2018

The electrostatic interactions were investigated between the zirconia and the 11-Mercaptoundecylphosphoric-acid layer formed on gold surfaces for their complex structures. For the investigation, the atomic force microscope was used to measure the surface forces between the surfaces as a function of the salt concentration and pH value. The forces were analyzed with the Derjaguin-Landau-Verwey-Overbeek theory to estimate the potential and charge density of the surfaces for each condition. The concentration dependence of the surface properties, found from the measurement at pH 4 and 8, was consistent with the prediction from the law of mass action. The pH dependence was explained with the ionizable groups on the surface. It was found that the 11-Mercaptoundecylphosphoric-acid layer had higher values for the surface charge densities and potentials than the zirconia surfaces at pH 4 and 8, which may be attributed to the ionized-functional-groups of the layer.