# Magnetization study of superconducting grains in Bi2.1Sr1.9CaCu2O8+δ

01 Nov 1995-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 253, Iss: 3, pp 225-230

TL;DR: In this article, the field dependence of DC magnetization was measured on a parallelepiped sample of superconducting Bi 2.1 Sr 1.9 CaCu 2 O 8+δ at different temperatures below T c with a maximum applied field of 160 kA/m. The experimental data extracted from the measured magnetization data was analyzed in terms of the Kim critical state model together with the surface barrier modified equilibrium magnetization.

Abstract: The field dependence of DC magnetization was measured on a parallelepiped sample of superconducting Bi 2.1 Sr 1.9 CaCu 2 O 8+δ at different temperatures below T c with a maximum applied field of 160 kA/m. The experimental intragranular magnetization extracted from the measured magnetization data was analysed in terms of the Kim critical state model together with the surface barrier modified equilibrium magnetization. Even though at low temperature ( T = 5 K) the experimental data could be explained by magnetization derived from the Kim model, the ‘Z’-shaped loops observed at higher temperatures could be explained only by taking into account the surface barrier modified equilibrium magnetization. Material-dependent parameters, such as critical current density as a function of field, fields for first flux entry ( H 1 ) and last flux exit ( H 2 ) and lower critical field ( H c1 ), were estimated. At higher temperatures, the contribution of equilibrium magnetization ( M eq ) is found to be dominating compared to the bulk magnetization. The possible reason for the significant contribution of equilibrium magnetization in granular superconductors is discussed.

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##### References

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IBM

^{1}TL;DR: Strong, anisotropic magnetic relaxation of the field-cooled and zero-field--cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal is reported and interpreted with a thermally activated flux-creep model.

Abstract: We report strong, anisotropic magnetic relaxation of the field-cooled and zero-field-cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal and interpret it with a thermally activated flux-creep model. A simple scaling argument shows that high thermal activation causes magnetic irreversibilities and critical currents to drop below the threshold of detectability at a reduced temperature difference $1\ensuremath{-}t$ proportional to ${H}^{\frac{2}{3}}$, a power frequently observed in experiment and in particular in our crystal.

1,358 citations

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General Electric

^{1}TL;DR: In this article, the interaction between a flux thread and the specimen surfuce of a semi-infinite type-II superconductor with a thread within it lying parallel to the single plane surface is considered to determine any low-field hysteresis in the magnetization curves of well-annealed, single-phase specimens.

Abstract: The interaction between a flux thread (quantized, fluxenclosing, supercurrent vortex) and the specimen surfuce of a semi-infinite type-II superconductor with a flux thread within it lying parallel to the single plane surface is considered to determine any low-field hysteresis in the magnetization curves of well-annealed, single-phase specimens. (R.E.U.)

762 citations

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IBM

^{1}TL;DR: The superconducting critical current in these films at 77 K is in excess of ${10}^{5}$ A/${\mathrm{cm}}^{2}$ and at 4.2 K in addition to this.

Abstract: We have grown epitaxial films of the ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ compound on ${\mathrm{SrTiO}}_{3}$ substrates. The superconducting critical current in these films at 77 K is in excess of ${10}^{5}$ A/${\mathrm{cm}}^{2}$ and at 4.2 K in excess of ${10}^{6}$ A/${\mathrm{cm}}^{2}$.

693 citations

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TL;DR: In this paper, the initial magnetization curves and complete hysteresis loops for hard type-II superconductors were calculated for an infinite orthorhombic specimen with finite rectangular cross section, 2a×2b (a≤b), in which a uniform field H is applied parallel to the infinite axis.

Abstract: We have calculated the initial magnetization curves and complete hysteresis loops for hard type‐II superconductors. The critical‐current density Jc is assumed to be a function of the internal magnetic field Hi according to Kim’s model, Jc(Hi)=k/(H0+‖Hi‖), where k and H0 are constants. As is the case for other critical‐state models, additional assumptions are that bulk supercurrent densities are equal to Jc, and that the lower critical field is zero. Our analytic solution is for an infinite orthorhombic specimen with finite rectangular cross section, 2a×2b (a≤b), in which a uniform field H is applied parallel to the infinite axis. Assuming equal flux penetration from the sides, we reduced the two‐dimensional problem to a one‐dimensional calculation. The calculated curves are functions of b/a, a dimensionless parameter p=(2ka)1/2/H0, and the maximum applied field Hm. The field for full penetration is Hp=H0[(1+p2)1/2−1]. A related parameter is H*m=H0[(1+2p2)1/2−1]. Hysteresis loops were calculated for the di...

579 citations