• 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.9 no.5
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• pp.251-255
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• 1999

NiFe(60 $\AA$)/Co(0$\AA$$\leq$x$\AA$$\leq$15$\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valve thin films were prepared on 4$^{\circ}$ tilt-cut Si(111) substrates with a 50 $\AA$ thick Cu underlayer without applying any external magnetic field during the deposition, and the effects of inserted ultrathin Co layer on magnetic anisotropy and GMR properties of the NiFe(60 $\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valves were investigated. As the ultrathin Co layer was inserted into the NiFe/Cu interface of the spin valves, GMR ratio was increased from about 1.5% to 3.5%, and the easy axis of NiFe(60 $\AA$) layer was rotated by 90$^{\circ}$. Accordingly, it was aligned along the same direction with the easy axis of Co(30 $\AA$)layer. Therefore, squared R-H curves was obtained in the spin valves, which is favorable properties for the digital GMR devices such as MRAM. In order to investigate the change of magnetic anisotropy of NiFe layer of the spin valves in more details,XRD measurement was performed using NiFe(500 $\AA$) and NiFe(500 $\AA$)/Co(10 $\AA$) thin films on the same templates. Strong (220) NiFe peak was observed in both films regardless of the inserted Co layer, so it was thought that the variation of magnetic anisotropy of NiFe layer is from the interface effect, the change of interface from NiFe/Cu to NiFe/Co, rather than the volume effect such as the change of magnetocrystalline effect.

• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.192-195
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• 2004

Magnetic properties by exchange biased perpendicular magnetic anisotropy in [Pd(0.8 nm)/Co(0.8 nm)]$_{5}$/FeMn(15 nm) multilayers deposited by dc magnetron sputtering system are investigated. As inserted Pd layer of interface between [Pd/Co] multilayer and FeMn film, the Hex of perpendicular anisotropy was improved from 127 Oe to 145 Oe. But result of an experiment by thermal stability, the Hex of the case that an inserted layer was inserted in decreased from low 20$0^{\circ}C$ in about 5$0^{\circ}C$ more if not inserted. If Ta was a buffer layer, the experiment results along material of buffer layer, the H$_{ex}$ obtained the largest 127 Oe. And if Pd was a buffer layer, H$_{ex}$ obtained the largest 169 Oe. Also, the Hc in buffer layer of Ta and Pd obtained the largest 203 Oe and 453 Oe, respectively.

• Korean Journal of Materials Research
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• v.10 no.10
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• pp.709-714
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• 2000

SAW 소자에 응용 가능한 자성박막재의 개발을 목적으로 RF 스퍼터링법으로 증착한 (Fe(sub)0.6Co(sub)0.4)(sub)89Zr(sub)11/Fe(sub)1-xCo(sub)x)Zr(sub)11(x=0, 0.6, 0.9)<원문잠조> 비정질 다층박막의 자기특성을 조사하였다. 수직자기장중열처리를 행하였을 때 상온에서 비자성 Fe(sub)89Zr(sub)11 층의 삽입에서만 다층박막화의 효과가 나타났다. 일 예로 (Fe(sub)0.6Co(sub)0.4)(sub)89Zr(sub)11(30${\AA}$)/Fe(sub)89-Zr(sub)11(40${\AA}$)<원문참조> 박막시편에 1kHz, 50 mOe의 여기자기장으로 평가된 최대 미분투자율${\mu}$(sub)d.max는 단층막의 750에서 1650으로 2배 이상 증가, 구동 바이어스자기장 Hw는 20 Oe에서 6Oe로 3배 이하로 감소하는 양호한 특성이 얻어졌다. 그러나 다른 중용 특성인 자왜는 34% 정도 감소하는 것으로 추정되었다.

• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.173-177
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• 2006

We have investigated the magnetoresistance (MR) effect of the spin valve structures composed of perpendicularly magnetized Pd/Co multilayers, with changing the space layer (Pd or Cu) thickness, the stacking number of the Pd/Co multilayers, and the Co insertion-layer thickness. The Cu space layer showed larger MR ratio than the Pd space layer. The Co insertion-layer between Cu layer and pinned layer enhanced the MR ratio about three times. The maximum MR ratio of 7.4 % was established in the sample with the Co insertion-layer thickness of 0.62 and 1.01 nm.

• Journal of the Korean Magnetics Society
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• v.27 no.4
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• pp.123-128
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• 2017

The magnetic isotropy property from the magnetoresistance (MR) curve and magnetization (MH) loop for the PtMn based spin valve (SV) multilayer films fabricated with different the bottom structure after post-annealing treatment was investigated. The exchange biased coupling field ($H_{ex}$), coercivity ($H_c$), and MR ratio of Glass/Ta(10 nm)/CoFe(6 nm)/Cu(2.5 nm)/CoFe(3 nm)/Ta(4 nm) SV multilayer film without antiferromagnetic PtMn layer are 0 Oe, 25 Oe, and 3.3 %, respectively. MR curve for the Glass/Ta(10 nm)/CoFe(6 nm)/Cu(2.5 nm)/CoFe(3 nm)/PtMn(6 nm)/Ta(4 nm) SV multilayer film showed $H_{ex}=2Oe$, $H_c=316Oe$, and MR (%) = 4.4 % with one butterfly MR curve having by the effect of antiferromagnetic PtMn layer. MR curve for the dualtype Glass/Ta(10 nm)/CoFe(6 nm)/Cu(2.5 nm)/CoFe(3 nm)/PtMn(6 nm)/CoFe(3 nm)/Cu(2.5 nm)/CoFe(6 nm)/Ta(4 nm) SV multilayer film showed $H_c=37.5Oe$ and 386 Oe, MR = 3.5 % and 6.5 % with two butterfly MR curves and square-like hysteresis MH loops. The anisotropy property in CoFe spin valve-PtMn multilayer is neglected by the effects of a very small value of $H_{ex}$ and a very slightly shape magnetic anisotropy. This result is possible to explain the effect of magnetization configuration spin array of the bottom SV film and the top SV film of PtMn layer.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.130-131
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• 2003

The magnetic and thermal properties of NiFe/IrMn/CoFe with Mn additions have been studied. As grown CoFe pinned-layers with IrMn-Mn have dominantly larger exchange biasing field( $H_{ex}$) and blocking temperature( $T_{b}$) than when pure I $r_{22}$M $n_{78}$ is used. The magnetic properties improve, $H_{ex}$ and $T_{b}$ improve with 77-78 vol% Mn, but drop considerably with more Mn additions, losing magnetic properties of theb NiFe/IrMn/CoFe with addition 0.6 vol % Mn. The average x-ray diffraction peak ratios fcc (111)CoFe of (111)IrM $n_3$ textures for the Mn inserted total vol of 75, 77, and 79 vol% were about 1.4, 0.8, and 0.6, respectively. For the sample without Mn inserted layer, the $H_{ex}$ between I $r_{22}$M $n_{78}$ and CoFe layers is almost nothing. For two multilayer as-grown samples with ultra-thin Mn layers of 77 vol % and 79 vol %, the $H_{ex}$s are 250 Oe and 150 Oe, respectively. In case of IrMn with 77.5 vol% Mn, the $H_{ex}$ was 444 Oe up to 30$0^{\circ}C$ endured of 363 Oe at 40$0^{\circ}C$, respectively. Mn additions improve the magnetic properties and thermal stabilities of NiFe/IrMn/CoFe. Those increase the $H_{ex}$ and $T_{b}$. In applications where higher $H_{ex}$ and $T_{b}$ are accept, proper concentrations of Mn can be used.n can be used.be used.

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.236-239
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• 2004

We studied the specular spin valve (SSV) having the spin filter layer (SFL) in contact with the ultrathin free layer composed of Ta3/NiFe2/IrMn7/CoFel/(NOLl)/CoFe2/Cu1.8/CoFe( $t_{F}$)/Cu( $t_{SF}$ )/(NOL2)/Ta3.5 (in nm) by the magnetron sputtering system. For this antiferromagnetic I $r_{22}$M $n_{78}$-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness ( $t_{F}$) and the SFL thickness ( $t_{SF}$ ) were 1.5 nm, and the MR ratio higher than 11% was maintained even when the $t_{F}$ was reduced to 1.0 nm. It was due to increase of specular electron by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field ( $H_{int}$) between free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer ( $H_{cf}$ ) was significantly reduced as compared to the traditional spin valve (TSV), and was remained as low as 4 Oe when the $t_{F}$ varied from 1 nm to 4 urn. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer.

• Journal of radiological science and technology
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• v.40 no.1
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• pp.93-99
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• 2017

Dose enhancement effects at megavoltage (MV) X and ${\gamma}-ray$ energies, and the effects of different energy levels on incident energy, dose enhancement agents, and concentrations were analyzed using Monte Carlo simulations. Gold, gadolinium, Iodine, and iron oxide ($Fe_2O_3$) were compared as dose enhancement agents. For incident energy, 4, 6, 10 and 15 MV X-ray spectra produced by a linear accelerator and a Co-60 ${\gamma}-ray$ were used. The dose enhancement factor (DEF) was calculated using an ICRU Slab phantom for concentrations of 7, 18, and 30 mg/g. The DEF was higher at higher concentrations of dose enhancement agents and at lower incident energies. The calculated DEF ranged from 1.035 to 1.079, and dose enhancement effects were highest for iron oxide, followed by iodine, gadolinium, and gold. Thus, this study contributes to improving the therapeutic ratio by delivering larger doses of radiation to tumor volume, and provides data to support further in vivo and in vitro studies.

• Microbiology and Biotechnology Letters
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• v.20 no.5
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• pp.574-582
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• 1992

Exo-xylanase encoded by the xylA gene of Bacillus stearothermoPhillus was produced from Escherichia coli ]M109 carrying a recombinant plasmid pMGL Synthesis of the enzyme was observed to be cell-associated, and about 94% of the enzyme synthesized was located in the cytoplasmic region. The maximum production was attained when the E. coli strain was grown at $37^{\circ}C$ for 8 hours on the medium containing 0.5% fructose, 1.0% tryptone, 1.0% sodium chloride, and 0.5% yeast extract. The exo-xylanase was purified to homogeneity using a combination of salting out with ammonium sulfate, DEAE-Sepharose CL-6B ion exchange chromatography, Sephadex G-IOO gel filtration, and Sephadex G-150 gel filtration. The' purified enzyme was most active at pH 6.0 and $45^{\circ}C$. $Ca^{2+}$ and $Co^{2+}$ activated the exo-xylanase activity by about 20% while $Ag^{2+}$, $Fe^{2+}$, $Mg^{2+}$ and $Zn^{2+}$ inhibited the enzyme activity by up to 60%. The $K_m$, value on p-nitrophenyl-$\beta$-D-xylanopyranoside was 2.75 mM. The enzyme had a pI value of 4.7. The estimated molecular weight of the native protein was 200,000 daL SDS-polyacrylamide gel electrophoresis analysis suggested that the native enzyme was a trimer composed of three identical 66,000 da!. polypeptides. The purified enzyme efficiently converted all the xylo-oligosaccharides tested to xylose. It was also confirmed that the enzyme split xylans in an exo-manner even though the degree of hydrolysis was fairly low. The xylanolytic enzyme was, therefore, classified to be one of the few bacterial exo-xylanases lacking transferase activity.