• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.370.1-370.1
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• 2014

Giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), and magnetic random-access memory (MRAM) are currently active areas of research. Magnetite, Fe3O4, is predicted to possess as half-metallic nature, ~100% spin polarization (P), and has a high Curie temperature (TC~850 K). On the other hand, Spinel ferrite CoFe2O4 has been widely studies for various applications such as magnetorestrictive sensors, microwave devices, biomolecular drug delivery, and electronic devices, due to its large magnetocrystalline anisotropy, chemical stability, and unique nonlinear spin-wave properties. Here we have investigated the magneto-transport properties of epitaxial CoxFe3-xO4 thin films. The epitaxial CoxFe3-xO4 (x=0; 0.4; 0.6; 1) thin films were successfully grown on MgO (100) substrate by molecular beam epitaxy (MBE). The quality of the films during growth was monitored by reflection high electron energy diffraction (RHEED). From temperature dependent resistivity measurement, we observed that the Werwey transition (1st order metal-insulator transition) temperature increased with increasing x and the resistivity of film also increased with the increasing x up to $1.6{\Omega}-cm$ for x=1. The magnetoresistance (MR) was measured with magnetic field applied perpendicular to film. A negative transverse MR was disappeared with x=0.6 and 1. Anomalous Hall data will be discussed.

• Bulletin of the Korean Chemical Society
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• 제35권2호
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• pp.494-500
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• 2014

Indium-doped zinc oxide nanocrystals (IZO NCs), capped with stearic acid (SA) of different sizes, were synthesized using a hot injection method in a noncoordinating solvent 1-octadecene (ODE). The ligand exchange process was employed to modify the surface of IZO NCs by replacing the longer-chain ligand of stearic acid with the shorter-chain ligand of butylamine (BA). It should be noted that the ligand-exchange percentage was observed to be 75%. The change of particle size, morphology, and crystal structures were obtained using a field emission scanning electron microscope (FE-SEM) and X-ray diffraction pattern results. In our study, the 5 nm and 10 nm IZO NCs capped with stearic acid (SA-IZO) were ligand-exchanged with butylamine (BA), and were then spin-coated on a thermal oxide ($SiO_2$) gate insulator to fabricate a thin film transistor (TFT) device. The films were then annealed at various temperatures: $350^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$, and $600^{\circ}C$. All samples showed semiconducting behavior and exhibited n-channel TFT. Curing temperature dependent on mobility was observed. Interestingly, mobility decreases with the increasing size of NCs from 5 to 10 nm. Miller-Abrahams hopping formalism was employed to explain the hopping mechanism insight our IZO NC films. By focusing on the effect of size, different curing temperatures, electron coupling, tunneling rate, and inter-NC separation, we found that the decrease in electron mobility for larger NCs was due to smaller electronic coupling.

• 한국자기학회지
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• 제11권5호
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• pp.189-195
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• 2001

ICP 마그네트론 스퍼터를 이용하여 2.5$\times$2.5 $\textrm{cm}^2$ 넓이의 열산화막이 형성된 실리콘 기판에 총 14개의 동일한 간격으로 NiFe(170 )/CoFe(48 )/Al(13 )-O/CoFe(500 )/Ta(50 ) 구조의 junction을 형성하여 자기저항비의 균일성을 알아보았다. 각 층은 ICP 마그네트론 스퍼터를 이용하여 만들고 특히 절연층은 플라즈마 산화법으로 제작하여 TMR 소자를 만들었다. 완성된 각 소자를 외부자기장을 변화시키면서 4단자 측정법으로 기준저항, 자기저항비, 자화반전자장을 측정하였다. 균일한 박막형성에 적합한 ICP스퍼터라도 같은 공정하에서 자기저항비의 표준편차가 2.72 정도의 분포가 있었으며, 위치에 따른 각 기준저항, 자기저항비, 자화반전자장의 유의차는 없었다. 또한 기준저항이 증가함에따라 자기저항비와 자화반전자장이 증가하는 경향이 있었으며, 이러한 현상은 균일하지 못한 절연막의 형성에 기인하는 것으로 판단되었다. 균일한 성막이 가능한 ICP 스퍼터로도 위치별로 절연막층 상태의 국부적 분산에 따라 표준편차가 기준저항의 경우 64.19, 자기저항비의 경우 2.72의 변화가 발생하여 실제적인 소자의 양산을 위해서는 산화막 형성공정의 개선이나 후열처리 등에 의한 균일화 공정이 필요할 것으로 생각되었다.