• Journal of the Korean Magnetics Society
• /
• v.17 no.3
• /
• pp.124-127
• /
• 2007

Magnetic tunnel junctions (MTJs), which consisted of amorphous CoFeSiB layers, were investigated. The CoFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with an emphasis given on understanding the effect of the amorphous free layer on the switching characteristics of the MTJs. CoFeSiB has a lower saturation magnetization ($M_s\;:\;560\;emu/cm^3$) and a higher anisotropy constant ($K_u\;:\;2800\;erg/cm^3$) than CoFe and NiFe, respectively. An exchange coupling energy ($J_{ex}$) of $-0.003\;erg/cm^2$ was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the Si/$SiO_2$/Ta 45/Ru 9.5/IrMn 10/CoFe 7/$AlO_x$/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nm) MTJs structure, it was found that the size dependence of the switching field originated in the lower $J_{ex}$ using the experimental and simulation results. The CoFeSiB synthetic antiferromagnet structures were proved to be beneficial for the switching characteristics such as reducing the coercivity ($H_c$) and increasing the sensitivity in micrometer size, even in submicrometer sized elements.

• Journal of the Korean Magnetics Society
• /
• v.6 no.2
• /
• pp.80-85
• /
• 1996

An externally applied magnetic field during annealing the $Nd_{2}Fe_{14}B/Fe_{3}B$ based spring magnet was found to enhance the exchange coupling between the hard and soft magnetic grains. More than 30 % increase in remanence values for melt-spun $Nd_{4}Fe_{73.5}Co_{3}(Hf_{1-x}-Ga_{x})B_{18.5}$(x=0, 0.5, 1.0) alloys was resulted from uniform distribution of $Fe_{3}B$, $\alpha$-Fe as well as $(Nd_{2}Fe_{14}B)$, and also from reduced grain size of those phases by 20 %. The result also showed that there is an optimum grain size exhibiting a high coercivity value which will be discussed in terms of previously simulated exchange coupling parameter.

• Resources Recycling
• /
• v.1 no.1
• /
• pp.44-50
• /
• 1992

The $\alpha$-FeOOH powders were prepared by allkaline and acidic method on the small scale plant from the waste pickling liquor of iron. $\alpha$-FeOOH, $\alpha-Fe_2O_3$, $Fe_3O_4$ and ${\gamma}-Fe_2O_3$ powders were examined by TEM, SEM, TG-DTA, X-ray diffraction, VSM and chemical analysis. The results obtained from the experiment could be summerized as follows : the reaction time for the preparation of $\alpha$-FeOOH was observed to be smaller in the case of alkaline method and the products was acicular with the size of about $0.5\mu\textrm{m}$. The color of $\alpha-FeOOH and $\alpha-Fe_2O_3$was lovely yellow and red, respectively. The magnetic properties of $Fe_3O_4$ obtained by the reduction of $\alpha-Fe_2O_3$in the $H_2$ atomosphere at $370^{\circ}C$ for 1 hour showed 367(Oe) and 82.7(emu/g).

• Carbon letters
• /
• v.13 no.3
• /
• pp.157-160
• /
• 2012

In this work, iron oxide ($Fe_3O_4$) nanoparticles were deposited on multi-walled carbon nanotubes (MWNTs) by a simple chemical coprecipitation method and $Fe_3O_4$-decorated MWNTs (Fe-MWNTs)/polypyrrole (PPy) nanocomposites (Fe-MWNTs/PPy) were prepared by oxidation polymerization. The effect of the PPy on the electrochemical properties of the Fe-MWNTs was investigated. The structures characteristics and surface properties of MWNTs, Fe-MWNTs, and Fe-MWNTs/PPy were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The electrochemical performances of MWNTs, Fe-MWNTs, and Fe-MWNTs/PPy were determined by cyclic voltammetry and galvanostatic charge/discharge characteristics in a 1.0 M sodium sulfite electrolyte. The results showed that the Fe-MWNTs/PPy electrode had typical pseudo-capacitive behavior and a specific capacitance significantly greater than that of the Fe-MWNT electrode, indicating an enhanced electrochemical performance of the Fe-MWNTs/PPy due to their high electrical properties.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.5
• /
• pp.183-189
• /
• 2014

This study was conducted to study the influence of Co and Fe on the color of glaze and diopside crystals in the diopside crystal glaze empirically produced and used by ceramic artists, in case of adding $Co_3O_4$ and $Fe_2O_3$. As a result, the color of glaze was blue when $Co_3O_4$ was added to the diopside crystal glaze and the diopside crystals appeared pastel violet with Co included. When $Fe_2O_3$ was added to the diopside crystal glaze, the color of glaze appeared brown and the color of diopside crystals was goldenrod with Fe included. The crystals precipitated on the surface of diopside consisted of diopside crystals and diopside precursors. With longer retention time, the amount of diopside precursors decreased and the amount of diopside crystals increased. Also, Co was more easily included by the diopside crystals than Fe was and crystallizability of dispside was improved in case of including Co. Including Fe lowered peak intensity of properties and partially dissolved the diopside crystals.

• Journal of the Korean Magnetics Society
• /
• v.5 no.1
• /
• pp.38-41
• /
• 1995

The effects of Nb and Cu additives as will as substitutional Co into $Nd_{4}Fe_{85.5}B_{10.5}$ melt-spun alloy were studied aiming for finding a $\alpha$-Fe based Nd-Fe-B composite alloys with high energy product. The addition of Nb and Cu to $Nd_{4}Fe_{85.5}B_{10.5}$ decreased the average grain size and increased the coercivity up to 207kA/m(2.6kOe), Further-more, the substitution of Co for Fe in $Nd_{4}Fe_{82}B_{10}Nb_{3}Cu_{1}$ alloy resulted in the decrease of the average grain size (<20nm) and improved the hard magnetic properties. The remanence, coercivity and energy product of optimally annealed $Nd_{4}Fe_{74}Co_{8}B_{10}Nb_{3}Cu_{1}$ alloy were 1.345, 219kA/m(2.75kOe) and $95.5kJ/m^{3}$(12MGOe), respectively.

• Journal of the Korean Chemical Society
• /
• v.55 no.3
• /
• pp.463-471
• /
• 2011

A novel $N_2O_2$ Schiff base ligand, N,N'-bis(4-methoxysalicylidene)phenylendiamine(4-$CH_3O$-Salphen), has been synthesized. It has been revealed that the compound is very useful for the spectrophotometric quantification of Fe(II) and Fe(III) ions in aqueous solutions, such as mineral water, hot spring water, sea water, and waste water. The optimum conditions for the quantitative analysis are the followings; [4-$CH_3O$-Salphen]=$4.0{\times}10^{-4}\;M$, DMF/$H_2O$=70/30(v/v), pH=3.4~3.8, T= at $55^{\circ}C$, and prereaction time=1.0 hr. The sample of single valence state was prepared by the preliminary oxidation or reduction using $H_2O_2$ ($5.0{\times}10^{-4}\;M$) and $NH_2OH{\cdot}HCl$ ($5.0{\times}10^{-4}\;M$). The quantitative analyses of Fe(II) and Fe(III) ion were performed by measuring the absorbance at 434 nm and 456 nm, respectively. The estimated mean values agreed well with the standard values within the range of 2.00~6.90%. The limit of detection was 27.9 ng/mL for Fe(II) and 55.8 ng/mL for Fe(III).

• Journal of the Korean Magnetics Society
• /
• v.10 no.5
• /
• pp.210-219
• /
• 2000

The magnetoresistance characteristics of FeN/Co/Cu/Co and FeN/Co/Cu/Co/Cu/Co/FeN multilayers using ferromagnetic iron-nitrides (FeN) has been studied. The microstructure of FeN film is the mixed ${\alpha}$-Fe and $\varepsilon$-Fe$_3$N phase on the condition that the flow rate of N$_2$ gas is over 0.4 sccm. The magnetoresistance effect is observed because of shape magnetic anisotropy induced by needle-shaped $\varepsilon$-Fe$_3$N phase. This magnetoresistance effect changes, because the degree that the shape magnetic anisotropy adheres to the adjacent Co pinned layer is varied according to the flow rate of N$_2$ gas and the thickness of FeN film. The best magnetoresistance effect is obtained on the condition that the thickness of Co free layer is 70 ${\AA}$ and the maximum MR ratio(%) value of 3.2% shows in the FeN(250 ${\AA}$)/Co(70 ${\AA}$)/Cu(25 ${\AA}$)/Co(70 ${\AA}$)/Cu(25 ${\AA}$)/Co(70 ${\AA}$)/FeN(250 ${\AA}$) mutilayer film which is fabricated at the N, gas flow rate of 0.5 sccm and the FeN film thickness of 250 ${\AA}$. Four steps are observed in the magnetoresistance curve owing to this difference of coercive force, because respective magnetic layers in the multilayer possess different coercive forces. These effects observed in these mutilayer films can be expected to application to the memory device the same MRAM as can carry out simultaneously four signals.

• Journal of the Korean Institute of Gas
• /
• v.2 no.2
• /
• pp.40-47
• /
• 1998

This study describes a synthesis of spinel-type $Fe_3O_4$ for decomposition of carbon dioxide, using $Fe_3O_4$ $7H_2O$ and NaOH, at $40^{\circ}C$ for 20 h. with change of their chemical equivalent ratio from 0.50 to 0.75, 1.00, 1.25 and 1.50, respectively. Addition of 0.1-1.00 mole percentage $NiCl_2,\;RhCl_3$ to the particles of $Fe_3O_4$, Prepared by reacting chemical equivalent ratio 1.00, afforced spinel $Fe_3O_4$. The structure of $Fe_3O_4$ and $NiCl_2,\;RhCl_3$-added $Fe_3O_4$ was investigated with XRD and SEM, respectively.

• Journal of Sensor Science and Technology
• /
• v.12 no.1
• /
• pp.10-15
• /
• 2003

$PbTiO_3$/P(VDF/TrFE) thin film for pyroelectric infrared sensor's sensing materials have been fabricated by spin coating technique. 65 wt% VDF and 35 wt% TrFE were for P(VDF/TrFE) powder. $PbTiO_3$ powder was used for a ceramic - polymer composites materials. Surface of composite thin film by ceramic fraction factor was observed by SEM. The $PbTiO_3$/P(VDF/TrFE) thin film capacitancy, dielectric constant and dielectric loss measured by impedence analyzer(HP4192A) and pyroelectric coefficient was measured by semiconductor parameter analyzer(HP4145B).