• Progress in Superconductivity
• /
• v.3 no.1
• /
• pp.23-27
• /
• 2001

We have investigated the mixed-state magnetoresistance of high quality c-axis-oriented MgB2 thin film for magnetic field from 0.5 T to 5.0 T, applied normal to ab-plane. The temperature dependence of magnetoresistance was well described by vortex glass and fluctuation theories for different temperature regimes. We observed glassy exponent of v(z-1)~3 and upper critical field of $H_{c2}$(0)~35 T, which is consistent with previous data obtained from direct $H_{c2}$(0) measurements. Interestingly, the thermally activated flux flow region was observed to be very narrow, suggesting that the pinning strength of this compound is very strong. This finding is closely related to the recent reports that the bulk pinning is dominant in $MgB_2$and the critical current density of $MgB_2$ thin film is very high, comparable to that of cuprate superconductor. The present results further suggest that $MgB_2$is beneficial to technical applications.ons.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.11
• /
• pp.1035-1040
• /
• 2003

High $T_{c}$ superconducting B $i_2$S $r_2$CaC $u_2$ $O_{8+d}$ (BSCCO2212) films were prepared by a metallorganic decomposition (MOD) method. The metal organic solution of BSCCO2212 was spin-coated on MgO (100) substrates at 3000 rpm for 1 min. To achieve a high critical current density, we controlled heat-treatment conditions and atmosphere. The films were annealed at temperature 75$0^{\circ}C$ ∼ 80$0^{\circ}C$ in $O_2$ or air. We obtained c-axis orientated BSCCO thin films on MgO substrates. The annealed sample at 77$0^{\circ}C$ with $O_2$ showed the critical temperature about 77 K and critical current denstity of 1.19 ${\times}$ 10$^{5}$ A/$\textrm{cm}^2$ about 13 K.

• Progress in Superconductivity
• /
• v.5 no.2
• /
• pp.109-113
• /
• 2004

MgB$_2$ and FeTi composites was prepared to study the effect of FeTi particles on superconductivity of MgB$_2$. The sample, which had contained magnesium, boron and FeTi particles, was synthesized by the Commercial Stainless Steel Tube Enveloping Technique(COSSET) at 92$0^{\circ}C$ for 2 hours. The structure and properties of the sample was investigated by XRD, SEM, and SQUID magnetometer. It was found that there was a little change of T$_{c}$ compared with pure MgB$_2$ superconductor in spite of high percentage of FeTi particles, and there was no proof of structure change of MgB$_2$ superconductor due to FeTi particles. But the high porosity which was appeared in the pure MgB$_2$ was disappeared in the composites. We conclude that FeTi particles do not influence the superconductivity of MgB$_2$ and it is expected that fe-Ti material system will be a good material for a tube of the PIT process and for a substrate of the film.m.

• Progress in Superconductivity and Cryogenics
• /
• v.20 no.4
• /
• pp.46-49
• /
• 2018

To improve in-field critical current densities ($J_c$) of $GdBa_2Cu_3O_{7-{\delta}}$ (GdBCO) coated conductors(CCs) fabricated by the reactive co-evaporation by deposition and reaction (RCE-DR) process, employing the nominal composition of Gd:Ba:Cu=1:1:2.5, we tried to refine the $Gd_2O_3$ particles trapped in the GdBCO superconducting matrix. For this purpose, we carefully selected the processing conditions on the stability phase diagram of GdBCO for this composition. By lowering the growth temperature of $Gd_2O_3$ in the liquid, we could refine the average particle size of $Gd_2O_3$ particles trapped in the GdBCO matrix and also achieve the zero-resistive transition temperatures ($T_{c,zero}$) of 92.3~94.2 K. Unfortunately, however, it was unsuccessful to achieve enhanced in-field $J_c$ values from these samples because of an air-contamination of the amorphous precursor film before its conversion into crystalline GdBCO film, suggesting that any exposure of the amorphous precursor film to air is fatal in obtaining high performance GdBCO CCs via the RCE-DR process.

• Progress in Superconductivity
• /
• v.3 no.1
• /
• pp.31-35
• /
• 2001

We investigated the temperature and magnetic field dependent optical properties of a$ MgB_2$ thin film in the far-infrared region. In the superconducting state, i.e. 5 K, we obtained the values of superconducting gap $2\Delta$ ~ 5.2 meV and $2\Delta$ $_{k}$ $B/T_{c}$ ~1.8. Although the value of$ 2\Delta$$B/T_{c}$ was nearly half of the BCS value, the $2\Delta$ seemed to follow the temperature dependence of the BCS formula. Under the magnetic field (H), the superconducting state became suppressed. Interestingly, we found that the normal state area fraction abruptly increased at low field but slowly increased at high field. It did not follow the H-dependences predicted for a s-wave superconductor (i.e. a linear dependence) nor for a s-wave one (i.e. $H^{1}$2/ dependence). We discussed the complex gap nature of $MgB_2$ in comparison with two gap and anisotropic s-wave scenarios.ios.

• Progress in Superconductivity and Cryogenics
• /
• v.26 no.1
• /
• pp.5-9
• /
• 2024

This study investigated the effect of Kr ion beam irradiation on the superconducting properties of Nb thin films, which are known for their high superconducting transition temperature (T_c) at ambient pressure among single elements. Using the Stopping and Range of Ions in Matter (SRIM) program, we analyzed the distribution of Kr ions and displacement per atom (DPA) after irradiation, finding a direct correlation between irradiation amount and DPA. In samples with stronger beam energy, deeper ion penetration, fewer ions remained, and higher DPA values were observed. X-ray diffraction (XRD) revealed that the Nb (110) peak at 38.5° weakened and shifted with increasing irradiation. T_c decreased in all samples after irradiation, more significantly in those with higher beam energy. Irradiation raised resistivity of the film and lowered the residual-resistivity ratio (RRR). AC susceptibility measurements were also consistent with these findings. This research could potentially lead to more efficient and powerful superconducting devices and a better understanding of superconducting materials.

• Progress in Superconductivity and Cryogenics
• /
• v.13 no.1
• /
• pp.6-11
• /
• 2011

The $BaHfO_3$ (BHO) buffer layer on the IBAD MgO template was turned to be effective for a successful fabrication of $GdBa_2Cu_3O_{7-{\delta}}$ (GdBCO) films with high critical current density ($J_c$). Both the BHO buffer layers and GdBCO films were prepared by pulsed laser deposition (PLD). The effects of the PLD conditions, including substrate temperature ($T_s$), oxygen partial pressure ($PO_2$), and deposition time on the in-plane texture, surface roughness, and microstructures of the BHO buffer layers on the IBAD MgO template were systematically studied for processing optimization. The c-axis oriented growth of BHO layers was insensitive to the deposition temperature and the film thickness, while the in-plane texture and surface roughness of those were improved with increasing $T_s$ from 700 to $800^{\circ}C$. On the optimally processed BHO buffer layer, the highest $J_c$ value (77 K, self-field) of 3.68 $MA/cm^2$ could be obtained from GdBCO film deposited at $780^{\circ}C$, representing that BHO is a strong candidate for the buffer layer on the IBAD MgO template.

• Progress in Superconductivity and Cryogenics
• /
• v.14 no.1
• /
• pp.44-47
• /
• 2012

The substantial improvement of the signal-to-noise ratio (SNR) can be achieved with small-size samples or low-field MRI system by high-temperature superconducting(HTS) RF coil. The typical HTS RF coil made of HTS thin film is expensive and is limited the coil geometry to planar surface coil. In this study, commercial Bi-2223 HTS tapes was used as RF coil for a 0.35T permanent MRI system. It has advantages of both much lower cost and easier fabrication over HTS thin film coil. SNR gain of the image obtained from the HTS RF coil over a conventional Cu RF coil at room temperature was about 2.4-fold and 1.9-fold using the spin echo pulse sequence and gradient echo pulse sequence respectively.

• 한국초전도학회:학술대회논문집
• /
• v.11
• /
• pp.19-19
• /
• 2001

• Progress in Superconductivity
• /
• v.4 no.2
• /
• pp.99-103
• /
• 2003

We studied the nonequilibrium superconductivity due to tunnel injection of polaronic quasiparticle (QP) from organic photoconductor. The transport properties of an organic copper (II) phthalocyanine (Cu -Pc)/d-wave superconductor were investigated in dark and under ultraviolet (UV) radiation for performance of a novel $high -T_{c}$ superconducting three terminal device. We observed that the injection of polaronic QP from the organic Cu -Pc film into the $Bi_2$S $r_2$$CaCuO_{8+{\delta}}$ film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. We could increase the current gain by UV excitation of the organic photoconductor injector. The tunneling spectroscopy of a Cu -Pc/BSCCO junction exhibited a small enhancement of the zero bias conductance peak under the W excitation. The above phenomena are of importance in developing optically controlled three terminal superconducting device.e.