• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.161.1-161.1
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• 2008

• 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 Magnetics
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• v.11 no.1
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• pp.25-29
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• 2006

Recent experiments have demonstrated high TMR ratios in MTJs with the MgO barrier [1,2]. The CoFeB/MgO/CoFeB junctions showed better properties than the CoFe/MgO/CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB/MgO [3]. The amorphous CoFeB with 20 at%B starts the crystallization at $340^{\circ}C$ [4] and this crystallization of the CoFeB helps obtaining the high TMR ratio. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization were studied in annealed MTJs. XPS depth profiles were utilized. TEM analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B-oxide was formed at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.293-297
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• 1992

The magnetic properties of the amorphous Fe/sub 32/Ni/sub 36/Cr/sub 14/P/sub 12/B/sub 6/ has been studied by Mossbauer spectroscopy in the temperature range of 88-400K. The analysis of the spectrum of B8K, the magnetic hyperfine field and quadrupole splitting are found to be 140.5kOe and almost zero, which means that the magnetic hyperfine field is randomly oriented with respect to the principal axes of the electric field gradient, respectively. The values of quadrupole splitting in paramagnetic phase with Tc=280K are independent on the changes of temperature. Debye temperature is found to be about 288k from the analysis of recoilless fraction.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.841-845
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• 1995

The effect of small addition of Nb on the electrical resistivity and Hall coeffcient of the amorphous $Fe_{83}Zr_{7}B_{10}$ alloy and annealed ones ones below the crystallization temperature were investigated, which has been considered to be suitable for high frequency core material. At room temperature, their resistivities $\rho$ and the spontaneous Hall coeffcients $R_{s}$ are $~1.6\;{\mu}{\Omega}m$ and $~3{\times}10^{-8}m^{3}/As$, respectively. $R_{s}$ and $\rho$ are decreased with increasing temperature from 100 K to room temperature. Side-jump effect was adopted to analyze the effect of the small variation of conentration and annealing. The quantity of $R_{s}/{\rho}^{2}$ at room temperature, which is directly related to the electronic structure of the mother alloy, remained almost a constant except as quenched one as it can be predicted from the side-jump effect. The unexpected temperature dependence of $R_{s}/{\rho}^{2}$ measured at low fields much below Tc is left as a question.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.772-777
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• 1995

The effect of small addition of Nb on the electrical resistivity and Hall coefficient of the amorphous $Fe_{83}Zr_{7}B_{10}$ alloy and annealed ones below the crystallization temperature were investigated, which has been considered to be suitable for high frequency core material. At room temperature, their resistivities $\rho$ and the spontaneous Hall coefficients $R_{s}$ are $~1.6\;{\mu}{\Omega}m$ and $~3{\times}10^{-8}m^{3}/As$, respectively. $R_{s}$ and $\rho$ are decreased with increasing temperature from 100 K to room temperature. Side-jump effect was adopted to analyze the effect of the small variation of concentration and annealing. The quantity of $R_{s}/{\rho}^{2}$ at room temperature, which is directly related to the electronic structure of the mother alloy, remained almost a constant except as quenched one as it can be predicted from the side-jump effect. We suggested the temperature dependence of $R_{s}/{\rho}^{2}$ can be compared to Ms{T}.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.122-125
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• 1994

The magnetic properties of Nd-Fe-B alloys of containing 4 at.% Nd have been studied for the development of new type rare-earth magnets. The amorphous phase of a melt-spun $Nd_{4}Fe_{85.5}B_{10.5}$ alloy is transformed into the phases which have a small amount of $Nd_{2}Fe_{14}B_{1}$ in ${\alpha}-Fe$ matrix by annealing above their crystallization temperature. The addition of Mo, Nb, V or Cu to $Nd_{4}Fe_{85.5}B_{10.5}$ alloy results in the reduction of grain size and the sub¬sequent improvement of the coercivity. The coercivity of $Nd_{4}Fe_{82}B_{10}M_{3}Cu_{1}$(M = Mo, Nb, V) alloys increases in the order of M = V < Nb < Mo and shows the highest value of 2.7 kOe when M = Mo. On the other hand, the rem¬anence of these alloys shows the opposite trend and the rn>st improved value of 1.35 T is observed when M = V.

• Journal of the Mineralogical Society of Korea
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• v.19 no.4 s.50
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• pp.265-275
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• 2006

It is in its infancy to use bacteria as a novel biotechnology for leaching precious and heavy metals from raw materials. The objective of this study was to investigate biogeochemical processes of iron leaching from magnetite reduction by iron-reducing bacteria isolated from intertidal flat sediments, southwestern part of Korea. Microbial leaching experiments were performed using commercial magnetite, Aldrich magnetite, in well-defined mediums with and without bacteria. Water soluble Fe production was determined by ICP analysis of bioleached samples in comparison to uninoculated controls, and the resulting precipitated solids were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The extent of iron leaching from magnetite in the aerobic conditions (Fe = 107 ppm) was higher than that in the anaerobic environments (Fe = 94 ppm). In the anaerobic conditions, Fe(III) in commercial magnetite was also reduced to Fe(II), but no secondary mineral phases were observed. Amorphous iron oxides formed in the medium under aerobic conditions where there was sufficient supply of oxygen from the atmosphere. SEM observation suggests that the reduction process involves dissolution-precipitation mechanisms as opposed to solid state conversion of magnetite to amorphous iron oxides. The ability of bacteria to leach soluble iron and precipitate amorphous iron oxides from crystalline magnetite could have significant implications for biogeochemical processes in sediments where Fe(III) in magnetite plays an important role in the largest pool of electron acceptor as well as the tool as a novel biotechnology for leaching precious and heavy metals from raw materials.

• Journal of the Korean Magnetics Society
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• v.8 no.4
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• pp.210-215
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• 1998

$Nd_{15}Fe_{77}B_8$ and $Nd_{16}Fe_{76}B_8$ powders were prepared by mechanical alloying in Ar atmosphere, and their phases and magnetic properties were investigated with as a function of the annealing temperature. It was found that the mechanical alloyed $Nd_{16}Fe_{76}B_8$ powder for 450 hours was amorphous phase with a part of $\alpha$-Fe crystallites. The obtained powders at 700 $^{\circ}C$ for 30 minute resulted in two phase of $Nd_2Fe_{14}B$ and $NdB_6$ by the solid-state reaction. The mechanical alloyed $Nd_{16}Fe_{76}B_8$ powder for 450 hour and annealed at 700 $^{\circ}C$ for 30 minute was showed $_iH_c\;of\;9.91\;kOe,\; B_{max}\;of\;12.93\;kG,\;Br\;of\;7.6\;kG\;and\;(BH)_{max}\;10.1\;MGOe$.

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.683-689
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• 2003

The cylindrical ${\gamma}$-alumina pellets were prepared using amorphous alumina and pore generating agent. Its were immersed in aqueous solution of the mixture of Fe(NO$_3$)$_3$.9$H_2O$ and $CH_3$COOH, Fe(NO$_3$)$_3$.9$H_2O$ and $CH_3$COOH and HNO$_3$, and Fe(NO$_3$)$_3$.9$H_2O$ and HNO$_3$. The pellets thus were hydrothermally treated at 20$0^{\circ}C$ for 3 h in autoclave, and were investigated morphologies and changes of crystal pore characteristics, $N_2$ adsorption and desorption isotherms, active sites and mechanical strength etc. According to the preparation method, acicular platelet pseudo-boehmite crystals of 0.1~0.3 ${\mu}{\textrm}{m}$ size were transformed into acicular pseudo-boehmite cristals of 0.5~2 ${\mu}{\textrm}{m}$ size having the same crystal structure. When ${\gamma}$-alumina pellets were immersed in aqueous solution of the mixture of Fe(NO$_3$)$_3$.9$H_2O$ and $CH_3$COOH and then were hydrothermally treated, pore volume between 100 $\AA$ and 1000 $\AA$ was increased from 0.34 ㏄/g to 0.86 ㏄/g, and the gap of $N_2$ adsorption and desorption hysteresis loop was decreased due to increasement of pore size. New active site that could adsorb the C-H functional group was created on the catalist. Also, mechanical strength of catalyst was increased from 1.06 ㎫ to 1.36 ㎫.