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RANOTMAHIPAL,성원경,정순길,강원남 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.6
Superconducting MgB2 thick films were fabricated on top of Ag or Cu/Al2O3 substrates at 560 ℃ by using hybrid physical-chemical vapor deposition (HPCVD). The Ag- or Cu-impurity layers were deposited on c-cut Al2O3 substrates at room temperature by using pulsed laser deposition (PLD). The influence of the thickness of the Ag- or the Cu-impurity layers on the microstructure and on the flux-pinning properties of the MgB2 films has been investigated. Scanning electron microscopy analysis revealed that MgB2 films grown on a thick impurity layer of Ag or Cu were denser than those grown on a thin layer. MgB2 films with Ag- or Cu-impurity layers showed a significant increase in the critical current density, Jc, as compared to the pure MgB2 film. The enhanced critical current density results from flux pinning caused by grain boundaries and by other type of defects introduced by the Ag- or the Cu-impurity layers. The peak position of the normalized flux-pinning force density, fp(b), curve shifts to lower reduced field with decreasing temperature for Ag- or Cu-doped films. This behavior indicates that different types of pinning centers and pinning mechanisms exist in the samples.
Fabrication details of Ba1-xKxFe2As2 films by pulsed laser deposition technique
이남훈,정순길,RANOTMAHIPAL,강원남 한국초전도.저온공학회 2014 한국초전도저온공학회논문지 Vol.16 No.3
Among Fe-based superconductors, potassium doped BaFe2As2 is favorable for applications because of its relatively hightransition temperature and low anisotropy. To study the superconducting properties and the applicable aspects, high quality thinfilms of potassium doped BaFe2As2 should be fabricate. However, the high volatility of potassium makes it difficult to fabricate thinfilms of this compound. In this paper, we discuss the details of the experimental conditions used to fabricate Ba1-xKxFe2As2 films byex situ PLD method. In the first set of samples, barium ratio in the target was controlled to make films with various potassiumdoping rate. However, in the second set of samples, the amount of potassium was controlled to find out optimal conditions formaking high quality Ba1-xKxFe2As2 films
강원남,정순길,성원경,N. H. Lee,RANOTMAHIPAL 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
We have investigated the flux pinning force in MgB2 thick films with columnar structures. Three types of thick lms with different grain sizes were prepared on c-cut Al2O3 substrates by using the hybrid physical-chemical vapor deposition method at 520, 540 and 560 ℃. For all of the samples, the pinning force densities showed an unusual double-peak behavior with two types of irreversible fields, H*, separating the peaks. This double-peak behavior of the pinning forces did not obey any flux pinning scaling laws, but could be well scaled by using separate pinning forces with the reduced irreversible fields bH H=Hirr and bL H=H*. These results suggest that these double-peak features are associated with two different pinning mechanisms, such as point defects in intragrains and planar defects between columnar grains. The latter pinning sources were observed to be stronger pinning centers compared to the former ones.
N.H. Lee,정순길,성원경,Eun-Mi Choi,RANOTMAHIPAL,강원남,Jinho Joo 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
High-quality MgB2 thin films have been fabricated by using the laser-assisted chemical vapor deposition (LACVD) method. For the in-situ LACVD process, we used a Mg target, Mg pieces, and a mixture of 5% B2H6 gas in H2. The Mg and the B sources were obtained from pulsed laser ablation and the inlet B2H6 gas, respectively. The MgB2 thin films were grown on Al2O3 (0001) substrates at various temperatures in the range of 160 – 400 C under pressures from 100 to 200 mTorr. As-grown samples showed superconducting transition temperatures (Tc) of 27 – 40 K. We obtained the best quality MgB2 thin film with a maximum Tc of 40 K at a substrate temperature of 400 C. The residual resistivity ratio (RRR) was observed to be about 4.4, which is similar to that of single-crystalline MgB2.
Ranot, Mahipal,Duong, P.V.,Bhardwaj, A.,Kang, W.N. The Korea Institute of Applied Superconductivity a 2015 한국초전도저온공학회논문지 Vol.17 No.2
$MgB_2$ thin films with superior superconducting properties are very promising for superconducting magnets, electronic devices and coated conductor electric power applications. A clear understanding of flux pinning mechanism in $MgB_2$ films could be a big aid in improving the performance of $MgB_2$ by the enhancement of $J_c$. The fabrication advancement and the understanding of flux pinning mechanism of $MgB_2$ thin and thick films fabricated by using hybrid physical-chemical vapor deposition (HPCVD) are reviewed. The distinct kind of $MgB_2$ films, such as single-crystal like $MgB_2$ thin films, $MgB_2$ epitaxial columnar thick films, and a-axis-oriented $MgB_2$ films are included for flux pinning mechanism investigation. Various attempts made by researchers to improve further the flux pinning property and $J_c$ performance by means of doping in $MgB_2$ thin films by using HPCVD are also summarized.
A safe and cost-effective PMMA carbon source for MgB<sub>2</sub>
Ranot, Mahipal,Jang, S.H.,Shinde, K.P.,Sinha, B.B.,Bhardwaj, A.,Oh, Y.S.,Kang, S.H.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.1
Carbon is proven to be very effective in pinning the magnetic vortices and improving the superconducting performance of $MgB_2$ at high fields. In this work, we have used polymethyl methacrylate (PMMA) polymer as a safe and cost effective carbon source. The effects of molecular weight of PMMA on crystal structure, microstructure as well as on superconducting properties of $MgB_2$ were studied. X-ray diffraction analysis revealed that there is a noticeable shift in (100) and (110) Bragg reflections towards higher angles, while no shift was observed in (002) reflections for $MgB_2$ doped with different molecular weights of PMMA. This indicates that carbon could be substituted in the boron honeycomb layers without affecting the interlayer interactions. As compared to undoped $MgB_2$, substantial enhancement in $J_c(H)$ properties was obtained for PMMA-doped $MgB_2$ samples both at 5 K and 20 K. The enhancement could be attributed to the effective carbon substitution for boron and the refinement of crystallite size by PMMA doping.
Ranot, Mahipal,Shinde, K.P.,Oh, Y.S.,Kang, S.H.,Jang, S.H.,Hwang, D.Y.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.3
Carbon coating approach is used to prepare carbon-doped $MgB_2$ bulk samples using low-cost naphthalene ($C_{10}H_8$) as a carbon source. The coating of carbon (C) on boron (B) powders was achieved by direct pyrolysis of naphthalene at $120^{\circ}C$ and then the C-coated B powders were mixed well with appropriate amount of Mg by solid state reaction method. X-ray diffraction analysis revealed that there is a noticeable shift in (100) and (110) Bragg reflections towards higher angles, while no shift was observed in (002) reflections for $MgB_2$ doped with carbon. As compared to un-doped $MgB_2$, a systematic enhancement in $J_c(H)$ properties with increasing carbon doping level was observed for naphthalene-derived C-doped $MgB_2$ samples. The substantial enhancement in $J_c$ is most likely due to the incorporation of C into $MgB_2$ lattice and the reduction in crystallite size, as evidenced by the increase in the FWHM values for doped samples.
Ranot, Mahipal,Jang, S.H.,Oh, Y.S.,Shinde, K.P.,Kang, S.H.,Chung, K.C. The Korea Institute of Applied Superconductivity a 2016 한국초전도저온공학회논문지 Vol.18 No.1
We have investigated the addition effect of NiO magnetic nanoparticles on crystal structure, microstructure as well as superconducting properties of $MgB_2$. NiO-added $MgB_2$ samples were prepared by the solid-state reaction method. The superconducting transition temperature ($T_c$) of 37.91 K was obtained for pure $MgB_2$, and $T_c$ was found to decrease systematically on increasing the addition level of NiO. X-ray diffraction (XRD) analysis revealed that no substitution of Ni for Mg in the lattice of $MgB_2$ was occurred. The microstructural analysis shows that the pure $MgB_2$ sample consists of plate shape $MgB_2$ grains, and the grains get refined to smaller size with the addition of NiO nanoparticles. At 5 K, high values of critical current density ($J_c$) were obtained for small amount NiO-added $MgB_2$ samples as compared to pure sample. The enhancement in $J_c$ could be attributed to the refinement of $MgB_2$ grains which leads to high density of grain boundaries in NiO-added $MgB_2$ samples.