Critical Current Characteristics and Flux Pinning in Fe-Based Pnictide Superconductor

2013 ◽  
Vol 750 ◽  
pp. 288-292
Author(s):  
Bao Rong Ni ◽  
Edmund S. Otabe ◽  
Masaru Kiuchi ◽  
Yan Wei Ma
Keyword(s):  
Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Flux Pinning ◽  
Ac Susceptibility ◽  
Pinning Mechanism ◽  
Temperature Dependences ◽  
Current Densities ◽  
Current Characteristics

The superconducting Ba1-xKxFe2As2(x = 0.4) single crystals were prepared by the so-called FeAs self-flux method. The critical temperature by ac susceptibility measurement was estimated to be about 36 K. The magnetic field and temperature dependences of critical current densities were investigated by an ac inductive measurement (Campbell’s method). Unlike the phenomenon of co-existence of the global and local critical current densities observed in many polycrystalline Fe-based superconducting pnictides, it was found that only a uniform critical current density (Jc) flows through the whole sample. The value of Jcat 20 K and 1 T was about 5×108A/m2, which is much smaller than the local critical current density observed in polycrystalline samples. This result implies that a dissimilarity of flux pinning mechanism exists between these two kinds of materials. The force-displacement characteristic of fluxoids in sample was investigated. The Labusch parameter was found to increase monotonously with increasing magnetic field, while the interaction distance was proportional to the fluxoid spacing. These results are consistent with the prediction based on a simple flux pinning mechanism.

Critical Current Density and Flux Pinning Properties in Superconducting MgB2 with and without SiC Doping

2013 ◽  
Vol 750 ◽  
pp. 293-297
Author(s):  
Wen Xu Sun ◽  
Bao Rong Ni ◽  
Akiyoshi Matsumoto ◽  
Hiroaki Kumakura
Keyword(s):  
Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
High Magnetic Field ◽  
Current Density ◽  
Flux Pinning ◽  
Critical Magnetic Field ◽  
Pinning Mechanism ◽  
Pinning Potential ◽  
Force Displacement

It is well known that SiC doping in superconducting MgB2 improves the upper critical magnetic field (Bc2) and the critical current density (Jc) under high magnetic field. However, the relationship between SiC doping and the flux pinning mechanism has not been clarified. In this study, several MgB2 samples with and without SiC doping were prepared by the conventional in situ powder-in-tube method. The critical current densities and the force-displacement characteristics of fluxoids in samples were investigated by an ac inductive measurement (Campbell’s method). The Labusch parameter (αL) and the interaction distance (di) were estimated from the obtained force-displacement profile. It was found that SiC doping enhances the values of αL, but does not change the characteristics of the magnetic field dependence of αL apparently. Namely, αL vs. B3/2 characteristics in the pure samples and SiC doped samples are almost the same. Such a result of αL properties implies that the pinning mechanism in the SiC doped samples could be consistent with the conventional pinning theory. On the other hand, di, which is considered to be proportional to the size of pinning potential, decreases rapidly with increasing magnetic field, especially in the pure samples. For high magnetic field region, the variations of di were deduced to be caused by flux creep. The depth of pinning potential, U0, was estimated by using the values of αL and di. The values of U0 give evidence of that SiC doping can prevent the flux bundles moving to another pinning center under high magnetic field.

Critical Current Densities in Bi2Sr2Cacu2O8+D

1989 ◽  
Vol 169 ◽  
Author(s):  
Shunji Nomura ◽  
Yutaka Yamada ◽  
Tomohisa Yamashita ◽  
Eriko Yoneda ◽  
Hisashi Yoshino ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Flux Pinning ◽  
Pinning Force ◽  
Critical Fields ◽  
Current Densities ◽  
Upper Critical Fields ◽  
The Magnetic Field

AbstractCritical current densities and upper critical fields were measured for a single crystal of the high Tc oxide superconductor, Bi2Sr2CaCu2O8+d, within the ab basal plane and along the c axis. The anisotropy in critical current densities was observed to be Jc⊥/Jc//=10 in agreement with the anisotropy in resistivity for the normal state. The magnetic field dependence of the critical current densities can be interpreted by the anisotropy in the upper critical fields. The scaling of the critical current density with the magnetic field was found. The critical current density scaled to zero at fields Bc2 in the ab plane and along the c axis which were in good agreement with the upper critical fields measured by transport.The anisotropy in flux pinning force density along the b axis, Fp//b, and along the a axis, Fp//a, was found to be Fp//b/Fp//a=3. The data provided strong evidence for flux pinning by the modulated structure in this system.

Anisotropic critical current density and flux pinning mechanism of Fe1+yTe0.6Se0.4 single crystals

2021 ◽  
Author(s):  
Yongqiang Pan ◽  
Nan Zhou ◽  
Bencheng Lin ◽  
Jinhua Wang ◽  
Zengwei Zhu ◽  
...  
Keyword(s):  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Current Density ◽  
Flux Pinning ◽  
Magnetic Hysteresis ◽  
Magnetic Hysteresis Loop ◽  
Pinning Force ◽  
Magnetization Relaxation ◽  
Pinning Mechanism

Abstract Fe1+yTe0.6Se0.4 has considerable application potential due to its large critical current density (J c) and high upper critical magnetic field (H c2). However, the uncertainty of the anisotropy of J c and the unclear flux-pinning mechanism have limited the application of this material. In this study, the J c in three directions were obtained from magnetic hysteresis loop measurements. A large anisotropy of J c ab /J c c ~ 10 was observed, and the origin of the anisotropy was discussed in details. Flux pinning force densities (F p) were obtained from J c, and a non-scaling behavior was found in the normalized pinning force f p[F p/F p-max] versus the normalized field h[H/H c2]. The peaks of pinning force shift from a high h to a low h with increasing temperature. Based on the vortex dynamics analysis, the peak shift was found to originate from the magnetization relaxation. The J c and F p at critical states free from the magnetic relaxation were regained. According to the Dew-Hughes model, the dominant pinning type in Fe1+yTe0.6Se0.4 clean single crystals was confirmed to be normal point pinning.

scholarly journals Температурные зависимости критических параметров неоднородных сверхпроводящих пленок

2021 ◽  
Vol 63 (8) ◽  
pp. 1035
Author(s):  
П.И. Безотосный ◽  
К.А. Дмитриева
Keyword(s):  
Magnetic Field ◽  
Critical Temperature ◽  
External Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Superconducting Films ◽  
Critical Magnetic Field ◽  
Temperature Dependences ◽  
Comparison Of The Results

The results of calculating the temperature dependences of the critical current density and critical magnetic field of thin inhomogeneous superconducting films are presented. Comparison of the results obtained for inhomogeneous films with the results of calculations for homogeneous ones showed that in both cases, the decrease in the critical magnetic field occurs according to the root law, and the critical current density changes according to a power law with a degree of 3/2 when approaching the critical temperature. Quantitatively, the critical current density for inhomogeneous films in the absence of an external magnetic field is lower than for homogeneous ones. In turn, the critical magnetic field of inhomogeneous films is much larger than the critical field of homogeneous films.

TRANSPORT CRITICAL CURRENT DENSITIES IN Y–Ag–Ba–Cu–O SUPERCONDUCTORS

1989 ◽  
Vol 03 (13) ◽  
pp. 981-986 ◽  
Author(s):  
M. MAJOROŠ ◽  
F. HANIC ◽  
M. POLÁK ◽  
M. KEDROVÁ
Keyword(s):  
Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
Field Dependence ◽  
Current Density ◽  
Magnetic Field Dependence ◽  
Powder Technology ◽  
Transport Critical Current Density ◽  
Current Densities ◽  
Ag Substitution

The influence of Ag substitution in amount of 2 mol% instead of Y, Ba and Cu in Y 1 Ba 2 Cu 3 O 7−x high temperature superconductor on magnetic field dependence of the critical current density at 77 K was studied. The samples were prepared by powder technology as well as by citrate method. An increase of transport critical current density as well as its smaller magnetic field dependence was found in case of substitution Ag → Y and Ag → Ba for samples prepared by both methods. In the magnetic field 9 T, the transport critical current density of the sample Y 0.98 Ag 0.02 Ba 2 Cu 3 O 7−x was 0.3 A/cm 2. On the other hand, substitution Ag → Cu lowers transport critical current densities in comparison with undoped samples. The effect of Ag substitution was more pronounced in samples prepared by powder technology.

Enhancement of critical current density in YBa2Cu3Ox superconductor by mechanical deformation

1993 ◽  
Vol 8 (2) ◽  
pp. 249-254 ◽  
Author(s):  
V. Selvamanickam ◽  
M. Mironova ◽  
K. Salama
Keyword(s):  
Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Stacking Faults ◽  
Mechanical Deformation ◽  
Dislocation Loops ◽  
Field Orientation ◽  
Pinning Mechanism ◽  
The Magnetic Field

The critical current density of melt-textured YBa2Cu3Ox superconductor has been enhanced by mechanical deformation at a high temperature. Hot deformation at 45° to both the slip plane (001) and the slip directions [100]/[010] has resulted in a high density of dislocation loops and stacking faults. The deformed samples are found to exhibit a critical current density (Jc) at Hc-axis as high as that at Ha-b plane at 1.5 T and 77 K. A Jc of 35300 A/cm2 has been achieved at Hc (1.5 T and 77 K) which is twice as high as that observed in undeformed samples. The enhanced Jc in this magnetic field orientation is attributed to pinning by the defects created by mechanical deformation. This pinning mechanism is found to be effective over a wide angle between the magnetic field and the a-b plane and thus results in a marked reduction in the critical current anisotropy.

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