Search

Inter-granular Sn particles affect transport and magnetic properties both in the normal and superconducting states of polycrystalline GdBa2Cu3O7−δ (GdBCO) superconductors drastically. Normal state resistivity at 300 K increases ~ 18.0 times as the concentration of Sn is increased. An unusual upturn in resistivity as a function of temperature curve with a dip is observed in GdBCO with 3.0 wt% of Sn in which suppression of superconducting phase transition has been observed. Current-voltage (IV) curves below Tc exhibit nonlinear features in composites of GdBCO and Sn. Magnetization (M) as a function of magnetic field (H) curves at 2.0 –20.0 K in GdBCO shifts strongly with the addition of 1.0 wt% Sn. We have extracted irreversible magnetization, lower critical field (Hc1) and magnetic critical density (Jcm) as a function of H at several T. The maximum pinning force density is 0.4 GN/m3 in GdBCO which is reduced in the Sn added GdBCO. [ABSTRACT FROM AUTHOR]

Both the transport critical current density at the zero magnetic field and magnetic critical current density in a composite system consisting of bulk YBCO superconductor and insulating BaTiO3 (BTO) have been studied using current–voltage (IV) and magnetization (M) as a function of magnetic field (H), respectively. Vortex pinning by insulating nanoparticles of BTO from the inter-granular network is investigated up to the magnetic field of 7.0 T. By analyzing magnetic critical current density the possibility of crossover from collective pinning (CP) to strong pinning (SP) and how it is affected by BTO have been explored based on the framework of Larkin–Ovchinnikov (LO) theory. Possible scenario of the strong pinning (SP) induced by insulating nanoparticles has also been studied using an exponent. [ABSTRACT FROM AUTHOR]

YBa 2 Cu 3 O 7−δ (YBCO) nanocomposite films were fabricated by low-fluorine metal-organic deposition (LF-MOD) route, combining self-seeding and multi-doping strategies with elements of Zr, Hf, Sn and Mn. Under the same growth conditions, due to the self-seeding layer as a template for the c -axis growth of doped films, all the multi-doped films with 200 nm self-seeding layers exhibit good c -axis orientation, even for the heavy doping of 16 mol%. EDS confirmed the four doping elements in the multi-doped YBCO films appear independently, leading to higher density of nano-scale heterogeneous phases than the case of Zr single doping. The pinning force density (F p) and critical current density (J c) are improved significantly, which indicates that the optimal doping content is achievable as high as 12 mol% in the case of multi-doping. The multi-12% YBCO films have the highest Fp,max of 6.13 GN/m3 at 77 K, which is about 3.3 times higher than that of the undoped films, and the Jc can reach 4.3 MA/cm2 at 30 K, compared to 3.1 MA/cm2 for the undoped films. [ABSTRACT FROM AUTHOR]

The critical current density, Jc, for Mg1−xTixB2 (0 ≤ x ≤ 0.1) samples has been calculated from magnetic hysteresis loop using Bean's model at different doping level and temperatures. The x = 0.075 sample shows the highest Jc compared with the other Ti-doped samples for all temperatures below 30 K. The reduced field dependence of normalized volume pinning forces has been analyzed at different temperatures and doping level. Fietz et al. and Eisterer scaling procedures have been used to analyze the pinning forces and determine the dominant pinning mechanism in all Ti-doped samples. The grain boundary pinning is found to be the dominant pinning mechanism in all the doped and undoped samples. The magnetic field at the pinning force peak was found to increase with the increase in Ti doping level. Moreover, we observed a suppression of anisotropy from clean to the dirty limit with increasing Ti concentrations. [ABSTRACT FROM AUTHOR]

Abstract In this paper we aimed at investigating the flux pinning property of MgB 2 films on hastelloy tapes which are buffered on various thicknesses of SiC layers. We have observed that the increase in thickness of the SiC buffer layer is very closely related with the systematic improvement of the field dependence of the critical current densities (J c) of MgB 2 tapes while the values of J c decreased. According to the analysis of the pinning force density (F p), there exist two pinning sources both in the pure MgB 2 and in the MgB 2 film with the thinnest SiC buffer layer. On the while, the pinning source observed in the MgB 2 films with thicker SiC buffer layers appears to be different from those previously mentioned. The different pinning behaviors of MgB 2 films may suggest that there be an additional pinning center working on the MgB 2 films with thick SiC buffer layers. The microstructural analyses of MgB 2 films confirmed that intra-granular defects and columnar grain boundaries may be a dominant pinning mechanism in the pure MgB 2 and the MgB 2 film with 170 nm-thick SiC buffer layer. For the MgB 2 films with thicker SiC buffer layers, carbon diffusion into the MgB 2 film, which is defined by the Auger electron spectroscopy, may be the origin of the additional pinning mechanism. Highlights • MgB 2 films were deposited on hastelloy substrate with different thickness of SiC buffer layer. • As the SiC buffer layer is thicken, pinning mechanism has changed. • Carbon diffusion into MgB 2 film seems to be an additional pinning source. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of laser irradiation on the superconducting properties of MgB, a pellet-shaped sample was produced and cut into two pieces. The dot-shaped molten patterns, with the distance of 100 µm between them, were formed on the surface of one of the pieces by using an Nd:YVO laser. The grains of the irradiated sample were significantly grown due to the laser-induced sintering. The modified surface appeared to have dense and compacted grains as a result of increasing interconnectivity among the superconducting grains. The critical current densities at 5 K in a field of 3 T were found to be 5.38 × 10 and 8.96 × 10 A cm for the reference and the irradiated samples, respectively. The increment of critical current density for the irradiated sample is presumably connected with the changing of pinning mechanism after the laser irradiation. For the irradiated sample which showed a higher value of critical current density at 5 K under high fields, Δ κ pinning was obtained as a dominant pinning mechanism, while the normal point pinning was dominant for the reference one. These results point out that the superconducting properties of bulk MgB can be changed and improved via laser irradiation in a short time. [ABSTRACT FROM AUTHOR]

The present study focuses on the effects of standby time of the MgB 2 samples immersed in synthetic engine oil on the critical current density (  J c ( H )), magnetic field dependence of the pinning force density f p ( b ) and T c performances of MgB 2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB 2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB 2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB 2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB 2 sample because of the number of the pinning centers. The MgB 2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The J c value for the pure sample is 2.0 × 10 3 A/cm 2 , whereas for the MgB 2 sample immersed at 300 min standby time in engine oil the J c is enhanced to 4.8 × 10 3 A/cm 2 at 5 K and 3 T. The superconducting transition temperature ( T c ) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300 min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB 2 superconductors. It was found that all MgB 2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB 2 bulk superconductors makes MgB 2 samples immersed in synthetic engine oil a good candidate for industrial applications. [ABSTRACT FROM AUTHOR]

Abstract: YBa2Cu3O7−δ–BaTiO3 (4wt.%) (YBCO–BTO (4%)) composite bulk polycrystalline sample has been synthesized by solid state reaction method. The structure of composite sample has been investigated by X-ray diffraction and magnetization measurements were carried out using MPMS SQUID VSM. The superconducting transition temperature of the YBCO–BTO (4%) sample was similar to that of pure YBCO. The critical current density (Jc ) for YBCO–BTO (4%) sample increases significantly as compared to pure YBCO sample. The enhancement of the critical current density in the YBCO–BTO (4%) sample has been attributed to the presence of BaTiO3 nanoparticles acting as artificial pinning centres. The introduction of BaTiO3 particles in YBCO increases pinning force density from 0.71GN/m2 to 1.41GN/m2 at 4K and 0.33MN/m2 to 0.97MN/m2 at 77K. [Copyright &y& Elsevier]

To improve on present critical current ( Jc) performance, multifilamentary Ag/Bi-2223 tapes with a large range of reduction rates were manufactured. The relative core mass density D was calculated, dependent on the measured geometric dimensions of the tapes. Experimental results, D vs. Jc, D vs. maximum pinning force density F max, and D vs. irreversible magnetic field Birr, are quantitatively formatted. In particular, the magnetic field dependence of Jc is critically dependent on its core density. If the core density increases by 10%, Jc of the tapes in this experiment is enhanced by as much as 100%. Therefore, in the present state of the technological process for manufacturing Ag/Bi-2223 tape, increasing the core density is clearly a significant strategy in improving the electronic and magnetic properties of the tapes and enhancing the capacity for carrying current at high magnetic fields. The limit of the bulk self-field- Jc can be calculated by the relationships of Jc vs. D. The limit is estimated to be on the order of 200 kA/cm2 for multifilamentary Bi-2223 tapes, which was supported by magneto-optical (MO) magnetization measurements results. It is a hard task to approach this limit with the present state of the art in manufacturing Ag/Bi-2223 tape, and it is the time to suggest some new ideals for Bi-2223 tapes to promote large-scale applications. [ABSTRACT FROM AUTHOR]

We present magnetization properties of magnesium diboride (MgB2). MgB2 polycrystals were fabricated by using the vapor transport method inside a sealed stainless tube. The critical current density Jc was estimated from the magnetization hysteresis ΔM by using the Bean model. The temperature dependence of Jc(T) showed a linear behavior below 15 K and deviated from such behavior in the higher temperature region. This behavior indicates that a flux creep effect influences the wide temperature range for the MgB2 polycrystals. Furthermore, small values of ΔM show that the pinning force density Fp is very weak. The temperature dependence of the upper critical field Hc2(T) was also obtained and revealed a linear behavior far from Tc. From our experimental results, we conclude that the MgB2 polycrystals are of good quality with less pinning centers, compared to the commercially available MgB2 powder. [Copyright &y& Elsevier]

DC magnetic properties of aligned (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ single crystals have been measured for the first time using a SQUID magnetometer in field up to 5 T and in the temperature range from 5 K to 150 K. The results confirm the existence of a broad temperature and field regime with completely reversible magnetization for these crystals. The temperature dependence of the irreversibility field H*(T) is determined from both M-H and M-T curves with fields oriented perpendicular to the ab plane of the crystal lattice. A strong field dependence of critical current density has been observed in these pristine single crystals with very weak pinning. These observations emphasize the importance of artificially introducing pinning sites in BSCCO material used for applications. Non-linear scaling models have been used to fit our experimental results to estimate the elemental pinning force density and the effective pinning potential. [ABSTRACT FROM PUBLISHER]

We made thin film multilayers of Nb/sub 0.37/Ti/sub 0.63//Nb and Nb/sub 0.37/Ti/sub 0.63//Ti (d/sub NiTi/=14-27 nm and d/sub N/=4-11 nm) to examine geometries and materials relevant to flux pinning in commercial NbTi conductors. Samples were characterized by transport measurements between 4.2 K and T/sub c/, in magnetic fields nearly parallel to the layers, up to 6 T. For some multilayers, pinning forces had a large peak at intermediate fields whose onset occurred near /spl sim/0.2 H/sub c2/. We suggest this peak effect is caused by a change in the vortex lattice structure, driven by the strong intrinsic pinning. We have measured the highest pinning force density (113 GN/m/sup 3/ at 4.2K and 5 T) ever achieved in the NbTi system. [ABSTRACT FROM PUBLISHER]

Abstract: The irreversibility line and flux pinning properties of high-Tc superconductor SmFeAsO0.85 were studied using DC magnetization data. Polycrystalline SmFeAsO0.85 was prepared in a high pressure synthesis apparatus under the pressure of 6GPa. The results of DC susceptibility showed the superconducting transition at about 55K. A critical current density Jc (B) was calculated using Bean’s critical state model. At low temperatures (⩽20K), Jc (B) showed a relatively high value with weak dependence on an applied magnetic field. At higher temperatures, a stronger dependence of the magnetic field was observed, which resulted from decrease in a critical current density probably due to the flux creep effect. The irreversibility line (IL) agreed well with the flux creep theory of Matsushita et al. A comparison of normalized pinning force density with the theoretical models showed that the irreversible behavior in SmFeAsO0.85 is dominated mainly by normal point pinning (δTc ) and surface pinning mechanisms. [Copyright &y& Elsevier]