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Journal ArticleDOI

Effect of oxygen-induced disorder on magnetic flux dynamics and critical current in a NdBa2Cu3O7-δ single crystal

01 Sep 2000-Superconductor Science and Technology (IOP Publishing)-Vol. 13, Iss: 9, pp 1356-1362
TL;DR: In this article, the magnetic flux dynamics in a large (4.3×3.8 mm3) single crystal NdBa2Cu3O7-δ sample was investigated under fully-oxygenated and oxygen-deficient conditions using vibrating sample magnetometry (VSM) and ac flux profile measurements in the B∥c-axis configuration.
Abstract: The magnetic flux dynamics in a large (4.3×3.4×2.8 mm3) single crystal NdBa2Cu3O7-δ sample was investigated under fully-oxygenated and oxygen-deficient conditions using vibrating sample magnetometry (VSM) and ac flux profile measurements in the B∥c-axis configuration. Using a split coil VSM the anisotropy (Γ) was determined. From the equilibrium magnetization above the irreversibility field (Birr), the London penetration depth (λ) was calculated. While a near total absence of the fishtail effect and more or less a constant J (15 000 A cm-2) in the field range of 1-10 T at 77 K was exhibited by the fully-oxygenated sample, a pronounced fishtail effect with an increase in current with a peak value of 32 000 A cm-2 was observed after oxygen reduction. However, the irreversibility field (Birr), was reduced from 13.1 to 7 T at 77 K after oxygen reduction. A vortex melting transition is indicated by the fully-oxygenated sample, with a marked deviation from this behaviour for temperatures below 86 K. A dynamic phase shift was observed through the superconducting transition which varies with field and exhibits a peak with a maximum around the irreversibility field.
Citations
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Journal ArticleDOI
TL;DR: In this article, the critical currents density and irreversibility field Hirr of (Cu1−xCx) Ba2Can−1CunO2n+4−δ ((Cu,C)-(n−1)n, n=3, 4 and 5) family were determined for the irradiated samples as well as unirradiated samples.
Abstract: For further enhancement of critical currents density Jc and irreversibility field Hirr of (Cu1−xCx) Ba2Can−1CunO2n+4−δ ((Cu,C)-(n−1)n, n=3, 4 and 5) family, pinning centers were introduced by ion and neutron irradiation in these compounds. The polycrystalline samples were irradiated with 3.6×1017 neutrons/cm2 or with Au15+ ions (240 MeV energy) at a fluence of 1×1011 ions/cm2. Jc and Hirr were determined for the irradiated samples as well as unirradiated samples. The intragrain Jc was evaluated from M–H curves using Bean's critical state model. In (Cu,C)-12(n−1)n, Jc (77 K, 1 T) shows a remarkable increase from 3.9×104 to 9.1×105 A/cm2 for neutron irradiated (Cu,C)-1234 and from 3.9×104 to 4.1×106 A/cm2 for heavy-ion irradiated (Cu,C)-1234. These results indicate the possibility of further enhancement of Jc and of achieving a very high Hirr of (Cu,C)-1234 in (Cu,C)-12(n−1)n family.

17 citations

Journal ArticleDOI
TL;DR: In this article, a technique for measuring the isothermal magnetocaloric coefficient (M_T$) is applied to the study of a superconducting NdBa$_2$Cu$_3$O$_7$ single crystal.
Abstract: A recently developed technique for measuring the isothermal magnetocaloric coefficient ($M_T$) is applied to the study of a superconducting NdBa$_2$Cu$_3$O$_7$ single crystal. Results are compared with magnetization ($M$) and specific heat ($C$). In the reversible region both $C$ and $M_T$ follow the scaling law of the 3D-xy universality class. The anomalies connected with flux-line lattice melting are visible on $M_T(B)$ curves as peaks and steps, similar to $C(T)$ curves yet with much smaller background. At lower temperature, in the irreversible region the $M_T(B)$ behaviour resembles more that of $M(B)$, exhibiting the "fishtail" effect. Our results confirm that the peculiarities of the phase diagram known from the high temperature superconductor YBa$_2$Cu$_3$O$_7$, e.g. vortex melting, dominance of critical fluctuations and absence of a $B_{c2}$ critical field line, are a common property of RE-123 systems.

11 citations

Journal ArticleDOI
T. Plackowski1, Yuxing Wang1, Rolf Lortz1, Alain Junod1, T. Wolf 
TL;DR: In this paper, a technique for measuring the isothermal magnetocaloric coefficient (MT) is applied to the study of a superconducting NdBa2Cu3O7 single crystal.
Abstract: A recently developed technique for measuring the isothermal magnetocaloric coefficient (MT) is applied to the study of a superconducting NdBa2Cu3O7 single crystal. Results are compared with magnetization (M) and specific heat (C). In the reversible region both C and MT follow the scaling law of the 3D-xy universality class. The anomalies connected with flux-line lattice melting are visible on MT(B) curves as peaks and steps, similar to C(T) curves yet with much smaller background. At lower temperature, in the irreversible region the MT(B) behaviour resembles more that of M(B), exhibiting the 'fishtail' effect. Our results confirm that the peculiarities of the phase diagram known from the high-temperature superconductor YBa2Cu3O7, e.g.?vortex melting, dominance of critical fluctuations and absence of a Bc2 critical field line, are a common property of RE-123 systems.

11 citations

Journal ArticleDOI
TL;DR: In this paper, the critical current density (J c ) and irreversibility field (H irr ) of (Cu 1− x C x )Ba 2 Ca n −1 Cu n O 2 n +4− δ ( n =4) were introduced by heavy-ion irradiation.
Abstract: To further enhance the critical current density ( J c ) and irreversibility field ( H irr ) of (Cu 1− x C x )Ba 2 Ca n −1 Cu n O 2 n +4− δ ( n =4; hereafter described as (Cu,C)-1234), pinning centers were introduced by heavy-ion irradiation. The polycrystalline samples were irradiated with Au 15+ ions (240 MeV energy) at various fluence of 3.5 × 10 10 , 6.5 × 10 10 , 1 × 10 11 , 2.5 × 10 11 and 5 × 10 11 ions/cm 2 . The intragrain J c was determined from M – H curves using Bean’s critical state model. With increase of the fluence, J c shows a rapid increase and reaches a maximum value, 4.1 × 10 6 A/cm 2 (77 K and 1 T) for the fluence of 1 × 10 11 ions/cm 2 and above which it decreases slowly. The maximum value of H irr (77 K), determined by extrapolating J c curves to a 10 3 A/cm 2 criterion, is about 14.5 T for the 2.5 × 10 11 ions/cm 2 . The α value in equation H irr ( T )= H irr (0)(1− T / T c ) α decreases from 2.97 for un-irradiated sample to 1.87 for the fluence of 1 × 10 11 ions/cm 2 . These results indicate the possibility of J c (77 K and 1 T) enhancement and reaching a high H irr (77 K) at the fluence of the 1.5 × 10 11 ions/cm 2 .

5 citations

Journal ArticleDOI
TL;DR: In this paper, the critical currents density (J c ) and irreversibility field (H irr ) of polycrystalline samples were determined for the irradiated samples as well as unirradiated samples.
Abstract: To enhance or improve critical currents density ( J c ) and irreversibility field ( H irr ) of (Cu,C)Ba 2 Ca 3 Cu 4 O 10.5− δ ((Cu,C)-1234), pinning centers were introduced by heavy-ion irradiation. The polycrystalline samples were irradiated with Au 15+ ions (240 MeV energy) at various fluence of 1×10 11 , 2.5×10 11 and 5×10 11 ions/cm 2 . J c and H irr were determined for the irradiated samples as well as unirradiated samples. J c (77 K, 1 T) increase from 3.9×10 4 A/cm 2 to 4.1×10 6 A/cm 2 for at fluence of 1×10 11 ions/cm 2 of heavy-ion irradiated sample and decreases with further increase of fluence. These results indicate the possibility of further enhancement of J c and of achieving a very high H irr of (Cu,C)-1234 below a fluence of 1×10 11 ions/cm 2 .

1 citations

References
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Journal ArticleDOI
TL;DR: A microstructure is realized which leads to very strong high-temperature flux pinning in YBa and Cu crystals, and causes a considerable enlargement of the irreversibility region in the H-T plane.
Abstract: We report the realization of a microstructure which leads to very strong high-temperature flux pinning in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ crystals. Aligned discontinuous columns of damaged material, about 50 \AA{} in diameter and more than 15 \ensuremath{\mu}m long, are produced by 580-MeV Sn-ion irradiation. The enhancement of flux pinning is largest when the applied magnetic field is aligned with these tracks. At high temperatures and fields the pinning is much greater than that produced by random point defects, and causes a considerable enlargement of the irreversibility region in the H-T plane.

960 citations

Journal ArticleDOI
01 Jul 1990-Nature
TL;DR: The anomalous magnetization characteristic, intra-grain granularity and the magnitude of the flux pinning in single crystals of YBa2Cu307-δ are intimately linked as mentioned in this paper.
Abstract: The anomalous magnetization characteristic, intra-grain granularity and the magnitude of the flux pinning in single crystals of YBa2Cu307–δ are shown to be intimately linked. As the nominal oxygen deficiency δ decreases towards zero, the flux pinning declines and the crystals lose their explicitly granular signature. As δ is seldom specifically controlled at levels below ˜0.05 in even the most carefully made materials, small oxygen deficiencies may contribute significantly to both the flux pinning and the weak-link properties.

620 citations

Journal ArticleDOI
TL;DR: In this paper, a dc magnetization measurement of Nd1+xBa2−xCu3Oy (Nd123) superconductors was performed in a reduced oxygen atmosphere.
Abstract: A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa2Cu3Oy (Nd123) superconductors possessing high superconducting transition temperature (Tc) with a sharp transition and large critical current density (Jc) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O2 in Ar exhibited the Tc of about 95 K and the transition width of 1.5 K with the applied field of 10 Oe. A four‐probe measurement showed the zero resistive transition Tc (R=0) of about 95 K. An anomalous peak effect in the magnetization hysteresis (M‐H) loops was commonly observed and lead to large magnetic Jc of 2×104 A/cm2 at 77 K and 2 T for the applied field H parallel to the c axis of a sample (H∥c). This achievement is attributable to a preferential formation of high Tc phase (x<0.1) among the Nd1+xBa2−xCu3Oy solid solutions in a reduced oxygen atmosphere.

602 citations

Journal ArticleDOI
TL;DR: Current-voltage measurements in clean, untwinned YBa 2 Cu 3 O 7 single crystals with picovolt voltage sensitivity and millikelvin temperature resolution in magnetic fields ranging up to 7 T find evidence for a melting transition in the vortex lattice which is hysteretic in both temperature and magnetic field.
Abstract: We report on current-voltage measurements in clean, untwinned ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ single crystals with picovolt voltage sensitivity and millikelvin temperature resolution in magnetic fields ranging up to 7 T. We find evidence for a melting transition in the vortex lattice which is hysteretic in both temperature and magnetic field. The measured thermal and magnetic hysteresis widths are related by the local slope of the phase boundary. This strongly supports the picture that, in the clean limit, the melting transition of the Abrikosov vortex lattice is a first-order phase transition.

338 citations

Journal ArticleDOI
TL;DR: In this paper, the authors showed that rare earth (RE) ions with large radii exhibit relatively low T c due to the presence of RE-Ba solid solution and that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere.
Abstract: REBa2Cu3Oy superconductors with rare earth (RE) ions with large radii (RE: La, Nd, Sm) exhibit relatively low T c due to the presence of RE-Ba solid solution. We have found that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere. We have also found that critical current densities of these superconductors are higher than those of melt processed YBa2Cu3Oy with fine Y2BaCuO5 inclusions in a high field region. The irreversibility line was also shifted toward the higher H-T region. We believe that flux pinning in these superconductors is ascribable to a finely distributed RE(Ba1-x , REx )2Cu3Oy phase in a good superconductive matrix.

301 citations