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Co-Cu 박막의 거대자기저항에 미치는 구조적인자의 영향
이희웅,김익준 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.1
Giant magnetoresistance(GMR) has been investigated for nano-granular Co_xCu_(100-x)(X = 10, 20, 30) sputtered films. Solid solutions were obtained in a wide range of concentration and the microstructure associated with the spinodal decomposition was observed by after-aging. Guinier radii, which were evaluated by small angle neutron scattering, of Co magnetic particles in the Co_xCu_(100-x)(X = 10, 20, 30) films aged at 773K for 1h were 1.3-1.5 ㎚ and the surface-to-volume ratio of Co magnetic particles increased with increasing Co concentration. The MR ratio of Co-Cu films aged at 773K for 1h has the largest value, 7.6%, in 20 at.% Co concentration and decreases in 30 at.% Co concentration. However, the field dependence in low field increased with increasing Co concentration. These behaviours were investigated in terms of the Co particle size, the surface-to-volume ratio and the inter-distance between the Co particles.
Fe3O4 소결체와 Fe 첨가 Fe3O4 소결체의 전기전도 및 자기저항효과
이희웅,김익준 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.5
Electrical transport and magnetoresistance characteristics were investigated for sintered Fe₃O₄-xFe (x = 0, 10, 20 wt.%) specimens. For composition dependence of Fe₃O₄-xFe specimens sintered at 500℃, the largest MR of 3.3% at 10 kOe was obtained in Fe₃O₄-10Fe specimen. It was found that this enhanced MR appears together with the appropriate excess resistance, which regarded as tunneling barrier, in the interparticle of Fe₃O₄. It indicates that the enhanced MR ratio arises from the spin dependent tunneling effect and can be explained with increased interparticle contacts. On the other hand, for the sintering temperature dependence of Fe₃O₄-xFe samples, the MR ratios decrease with the increased sintering temperature. The decreased MR ratios for Fe₃O₄-xFe may be associated with the decreased resistance due to the growth of Fe₃O₄ particles in Fe₃O₄ specimen and inadequately increased tunneling barrier of Fe_(l-x)O particles in Fe₃O₄-10, 20Fe specimens.
Fe₃O₄ 소결체의 자기저항효과 및 감도개선에 관한 연구
이희웅,김익준 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8
Magnetoresistance effects have been investigated for Fe₃O₄ samples sintered with three type Fe₃O₄ powders; commercial Fe₃O₄ powders, Fe₃O₄ powders milled in Ar and ethyl alcohol. The largest MR ratio, 8% at 10kOe, was obtained in Fe₃O₄ sample sintered with powders milled in ethyl alcohol. The enhanced MR ratio appears together with the excess resistance, which regarded as tunneling barriers, at the interface between Fe₃O₄ particles. It indicates that the enhanced MR ratio arises from the spin dependent tunneling effect and can be explained with increased interparticle contacts. On the other hand, high sensitivities of Fe₃O₄ samples at low magnetic fields were achieved by fabricating the rod and ring type hybrid structure, Fe_(19)Ni_(81)/Fe₃O₄/ Fe_(19)Ni_(81). Compared with the MR values, 4%, at 2kOe for single Fe₃O₄ sintered body, same MR values for rod and ring type hybrid structures were obtained at 120Oe and 58Oe, respectively. These high sensitivities at low magnetic fields were attributed to magnetic fields increased by high permeability of Fe_(19)Ni_(81), at the space between the Fe_(19)Ni_(81) bulks.
Fe-Mn-Cr-Ni 계 오스테나이트 스테인리스강에서 질소의 용해거동
이희웅,김봉서,권해웅,김형걸,유경재 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.2
Induction melting method under pressurized nitrogen gas was used to produce austenitic stainless steels dissolved with high content of nitrogen. Fe-Mn-Cr-Ni allay system was melted using Cr-nitride ferrous allay(6wt.% N) as a main additive element. The concentration and dissolution behaviors of nitrogen in as-casted alloys were investigated to clarify the effectiveness of induction melting method under pressurized nitrogen gas and Cr-nitride ferrous alloy in producing high nitrogen austenitic stainless steels having excellent mechanical, corrosion-resistance and non-magnetic properties. Nitrogen concentration in molten alloys was increased with increasing nitrogen pressure up to 1.5 atm. This result can be explained by Sievert's law. The nitrogen concentration of about 6.900 ppm was obtained in a molten alloy when melted at the nitrogen pressure of 1.5 atm. XRD and XPS measurements were carried out to investigate the dissolution behavior of nitrogen in a molten alloy. Although it was failed to detect some nitrides by XRD, XPS measurement revealed the existence of nitride such as Cr₂N. Therefore it can be concluded that the dissolved nitrogen in a molten alloy exists as two states, one is as a solid solution state, the other is as a nitride state. It seems reasonable to conclude the most of nitrogen were dissloved as a solid solution state, and some nitrogen are apt to be formed into a nitride.