• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.315-319
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• 2005

To obtain low switching field ($H_{SW}$) we introduced amorphous ferromagnetic $Co_{70.5}Fe_{4,5}Si_{15}B_{10}$ single and synthetic antiferromagnet (SAF) free layers in magnetic tunnel junctions (MTJs). The switching characteristics for MTJs with structures $Si/SiO_2/Ta$ 45/Ru 9.5/IrMn 10/CoFe 7/AlOx/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nm) were investigated and compared to MTJs with $Co_{75}Fe_{25}$ and $Ni_{80}Fe_{20}$ free layers. CoFeSiB showed a lower saturation magnetization of $560 emu/cm^3$ and a higher anisotropy constant of $2800\;erg/cm^3$ than CoFe and NiFe, respectively. An exchange coupling energy ($J_{ex}$) of $-0.003erg/cm^2$ was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the CoFeSiB single and SAF free layer MTJs, it was frond that the size dependence of the $H_{SW}$ originated from the lower $J_{ex}$ experimentally and by micromagnetic simulation based on the Landau-Lisfschitz-Gilbert equation. The CoFeSiB SAF structures showed lower $H_{SW}$ than that of NiFe, CoFe and CoFeSiB single structures. The CoFeSiB SAF structures were proved to be beneficial far the switching characteristics such as reducing the coercivity and increasing the sensitivity in micrometer to submicrometer-sized elements.

• Journal of the Korean Chemical Society
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• v.25 no.5
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• pp.318-324
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• 1981

The effects of$ Fe_2O_3$ aggregation on the sintering of Ba-ferrite (BaFe$_{12}O_{19}$) were studied. $BaCO_3-Fe_2O_3$ mixtures were prepared by partial precipitation mixing and ball-mill mixing method using two different $Fe_2O_3 $powders. Techniques employed were TG, XRD and SEM. X-ray diffraction analysis showed that the over all reaction basically consists of the two consecutive reaction; $BaCO_3 + 6Fe_2O_3\;{\longrightarrow}\;BaFe_2O_3 + 5Fe_2O_3 + CO_2{\uparrow}\;BaFe_2O_4 + 5Fe_2O_3 \;{\longrightarrow}\;BaFe_{12}O_{19}$ It is also shown that the aggregation state of $Fe_2O_3$ raw materials, as well as the mixing method, has a remarkable effect on solid state reaction between $BaCO_3\;and\;Fe_2O_3$.

• Journal of the Korean Magnetics Society
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• v.11 no.5
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• pp.196-201
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• 2001

The dependence of CoFe interfacial layer thickness and plasma oxidation condition on tunneling magnetoresistance (TMR) in Ta/NiFe/FeMn/NiFe/Al$_2$O$_3$/NiFe/Ta tunnel junctions was investigated. As the CoFe layer thickness increases, TMR ratio rapidly increases to 13.7 % and decreases with further increase of the CoFe layer thickness. The increase of TMR with the CoFe thickness up to 25 was thought to be due mails to the high spin-polarization of CoFe. The maximum MR of 15.3% was obtained in the Si(100)/Ta(50 )/NiFe(60 )/FeMn(250 )/NiFe(70 )/Al$_2$O$_3$/NiFe(150 )/Ta(50 ) magnetic tunnel junction with a 16 Al oxidized for 40 sec using a Ar/O$_2$ (1:4) mixture gas.

• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.244-248
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• 1994

Magnetic and Magneto-optical characteristics of NdTbFeCo alloy films and NdTbFeCo/TbFeCo double-layered films have been investigated. It was observed that the Kerr rotation(${\theta}_{k}$) in the short wavelength region increased and the coercivity decreased as the substitutional amount of Nd for Tb in NdTbFeCo film at the constant FeCo content. In spite of the increased ${\theta}_{k}$, a small coercivity of NdTbFeCo film made this medium unsuitable for magneto-optical recording medium at short wavelength. An effort was made to improve coercivity by exchange coupling with TbFeCo film of high coercivity. In the exchange-coupled $Nd_{16.9}Tb_{15.2}Fe_{50.4}Co_{17.5}(150\;{\AA})/Tb_{21.1}Fe_{65.0}Co_{13.9}(300\;{\AA})$ double-layered film, the magnetization reversal switching field and the Kerr rotation angle were increased to about 6.0 KOe and $0.32^{\circ}$ at 500 nm, respectively. This result indicates that exchange-coupled NdTbFeCo/TbFeCo film can be a promising candidate for agneta-optical rerding medium short wavelenhth.

• Journal of the Korean Magnetics Society
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• v.9 no.2
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• pp.104-110
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• 1999

The effect of the composition and the heat treatment on the magnetic and magnetoresistance properties in AgCo alloy films and Fe/AgCo/Fe trilayers prepared by the co-evaporation method were studied. As the alloy film thickness decreases, especially below 50 nm thick, the magnetoresistance decreases and the saturation field increases significantly. The change of the Co content, heat treatment, and deposition of the Fe under/over-layer were effective to prevent the reduction of the and the increasing of the saturation field. For 40 at.%Co sandwiches, the minimum saturation field was obtained in the 20 nm alloy film with 30nm Fe under-over layer annealed at 300 $^{\circ}C$ for 10 min. Its saturation field and the MR ratio were 1.01 kOe 5.16% respectively.

• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.196-202
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• 2000

Top synthetic spin valves with structure Ta/NiFe/CoFe/Cu/CoFe(P1)/Ru/CoFe(P2)/FeMn/Ta on Si(100) substrate with natural oxide were prepared by dc magnetron sputtering system, and investigated on the magnetoresistance properties and effective exchange bias field. As the thickness of FeMn increased above 150 $\AA$, MR ratio was decreased due to the current shunting effect. As the thickness of free layer decreased below 40$\AA$, MR ratio was reduced rapidly. In case of 40 $\AA$ thick of free layer, spin valve film with a structure Si(100)/Ta(50 $\AA$)/NiFe(27 $\AA$)/CoFe(13 $\AA$)/Cu(26 $\AA$)/CoFe(30 $\AA$)/Ru(7 $\AA$)/CoFe(15 $\AA$)/FeMn(100 $\AA$)/Ta(50 $\AA$) exhibited maximum MR ratio of 7.5 % and an effective exchange bias field of 600 Oe, respectively. Thickness difference dependence in this synthetic spin valve structure on effective exchange field was investigated and interpreted by the analytical method. It should be noted that thickness increase of CoFe(P 1) and decrease of CoFe(P2) in synthetic antiferromagnet leaded to the decrease in effective exchange bias field by experimentally and analytically.

• Journal of Powder Materials
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• v.10 no.5
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• pp.333-336
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• 2003

The purpose of this study is the fabrication of nano-sized Fe-Co alloy powders with soft magnetic properties by the slurry mixing and hydrogen reduction (SMHR) process. $FeCl_2$0 and $CoCl_2$ powders with 99.9% purities were used for synthesizing nanostructured Fe-Co alloy powder. Nano-sized Fe-Co alloy powders were successfully fabricated using SMHR, which was performed at 50$0^{\circ}C$ for 1 h in H$_2$ atmosphere. The fabricated Fe-Co alloy powders showed $\alpha$' phase (ordered body centered cubic) with the average particle size of 45 nm. The SMHR powder exhibited low coercivity force of 32.5 Oe and saturation magnetization of 214 emu/g.

• Journal of the Korean Magnetics Society
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• v.22 no.1
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• pp.1-5
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• 2012

We investigate the exchange bias effect in $[Pd/Co]_5$ superlattice structures which are representative system of the perpendicular magnetic anisotropy. We fabricate Si/$[Pd/Co]_5$/FeMn structures, and study the exchange bias variations by measuring hysteresis loop variations with thickness of FeMn layer. In order to optimize the perpendicular magnetic anisotropy, we fix the thickness of Pd with 1.1 nm and investigate the dependence of the perpendicular magnetic anisotropy on the ferromagnetic Co layer thickness. As results, we find that the biggest coercivity in 0.3 nm of Co layer without FeMn layer. The biggest exchange bias field is found for 0.3 nm of Co layer when we change the Co thickness with fixed FeMn thickness. When we vary thickness of FeMn layer, the biggest coercivity is found for 5 nm of FeMn layer. No exchange bias is observed when the FeMn layer is thinner than 3 nm, and the exchange bias field increases with FeMn layer thickness continuously up to 15 nm.

• Applied Chemistry for Engineering
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• v.16 no.2
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• pp.206-211
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• 2005

Mediated electrochemical oxidation (MEO) of polyethylene glycols (PEGs) of molecular weight of 1000, 4000 and 20000, was carried out on both platinum (Pt) and titanium-iridium electrodes in 8.0 M nitric acid solution containing 0.5 M Fe(II) and Co(II) ion. The electrochemical parameters such as current densities, kinds of electrode, electrolyte concentration and removal efficiency were investigated in both Fe(III)/Fe(II) and Co(III)/Co(II) redox systems. The PEGs was decomposed into carbon dioxide by MEO in Fe(III)/Fe(II) and Co(III)/Co(II) redox system during 180 min and 210 min at the current density of $0.67A/cm^2$ on the Pt electrode. Removal efficiency of PEGs by MEO was better in Co(III)/Co(II) redox system than Fe(III)/Fe(II) redox system, indicating mediated electrochemical removal efficiency was 100%.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.2
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• pp.143-150
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• 2002

The thermal behavior of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ prepared by a co-precipitation wasinvestigated for Hz generation by the thermochemical cycle. The reduction reaction of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ started from $480^{\circ}C$, and the weight loss was 1.6 wt% up to $1100^{\circ}C$. At this reaction, $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ was reduced by release of oxygen bonded with the $Fe^{3+}$ ion in the B site of ($CO_{0.5}$ $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$. In the $H_2O$ decomposition reaction, $H_2$ was generated by oxidationof reduced $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$. The crystal structure of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ for reduction reaction maintained spinel structure and the lattice constant of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ ($8.41\AA$) was enlarged to $8.45\AA$. But the lattice constant of $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ after $H_2O$ decomposition reaction did not change to $8.45\AA$. Then, $(Co_{0.5}\;Mn_{0.5})Fe_2O_4$ is excellent material in the thermochemical cyclic reaction due to release oxygen at low temperature for the reduction reaction and produce $H_2$ maintaining crystal structure for redox reaction.