Evidence for nonlinear flux diffusion from magnetization relaxation in Bi2Sr2CaCu2O8 single crystals

Kozioł, Z.; Châtel, P.F. de; Franse, J.J.M.; Tarnawski, Z.; Menovsky, A.A.

doi:10.1016/0921-4534(93)90494-b

Cited by 6 publications

(2 citation statements)

References 32 publications

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“…Based on the concept of self-organized criticality or avalanche dynamics (Bak et al 1988, Tang and Bak 1988, Tang 1993, Field et al 1995, Wang and Shi (1993) derived an expression J(t) = J c −J c [(k B T /U 0 ) ln(1+βt/τ )] 1/β which is similar to (9.16) and for β = 1 coincides with the Kim-Anderson result, see also the measurements of creep by micro Hall probes by Koziol et al (1993). Good fits to relaxation rates are also achieved by fitting a spectrum of activation energies (Hagen and Griessen 1989, Griessen 1990, Gurevich 1990, Niel and Evetts 1991, Martin and Hebard 1991, Theuss et al 1992, Theuss 1993.…”

Section: Flux Creep and Activation Energysupporting

confidence: 55%

The flux-line lattice in superconductors

1995

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Magnetic flux can penetrate a type-II superconductor in form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons) each carrying a quantum of magnetic flux φ 0 = h/2e. These tiny vortices of supercurrent tend to arrange in a triangular flux-line lattice (FLL) which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-T c superconductors (HTSC's) also by thermal fluctuations. Many properties of the FLL are well described by the phenomenological Ginzburg-Landau theory or by the electromagnetic London theory, which treats the vortex core as a singularity. In Nb alloys and HTSC's the FLL is very soft mainly because of the large magnetic penetration depth λ: The shear modulus of the FLL is c 66 ∼ 1/λ 2 , and the tilt modulus c 44 (k) ∼ (1 + k 2 λ 2 ) −1 is dispersive and becomes very small for short distortion wavelength 2π/k ≪ λ. This softness is enhanced further by the pronounced anisotropy and layered structure of HTSC's, which strongly increases the penetration depth for currents along the c-axis of these (nearly uniaxial) crystals and may even cause a decoupling of two-dimensional vortex lattices in the Cu-O layers. Thermal fluctuations and softening may "melt" the FLL and cause thermally activated depinning of the flux lines or of the two-dimensional "pancake vortices" in the layers. Various phase transitions are predicted for the FLL in layered HTSC's. Although large pinning forces and high critical currents have been achieved, the small depinning energy so far prevents the application of HTSC's as conductors at high temperatures except in cases when the applied current and the surrounding magnetic field are small.

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Section: Flux Creep and Activation Energysupporting

confidence: 55%

The flux-line lattice in superconductors

1995

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“…Other models not included in the above categories have also been proposed. For example, the recent concept of self-organized criticality (Bak et al, 1987) was applied to flux creep in high-temperature superconductors (Koziol et al, 1993;Tang, 1993; see also Richardson et al, 1994;Field et al, 1995;Reichhardt et al, 1995). These approaches are still too premature to be reviewed here.…”

Section: Theoretical Approaches To Magnetic Relaxation In High-tementioning

confidence: 99%

Magnetic relaxation in high-temperature superconductors

1996

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We review experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation. This effect has its origin in motion of flux lines out of their pinning sites due to thermal activation or quantum tunneling. The combination of relatively weak flux pinning and high temperatures leads to rich properties that are unconventional in the context of low temperature superconductivity and that have been the subject to intense studies. The results are assessed from a purely experimental perspective and discussed in the context of present phenomenological theories. [S0034-6861(96)00403-5] CONTENTS I. Introduction 911 II. Basic Concepts 914 A. Flux exclusion and flux lines in superconductors 914 B. The vortex lattice 915 C. Defected superconductors: irreversible magnetic properties 916 D. The critical-state model 917 E. Magnetic relaxation: basic mechanism 918 III. Overview of Magnetic-Relaxation Experiments 920 A. Experimental issues in magnetic-relaxation measurements 920 1. Sample inhomogeneities 920 2. Field inhomogeneities in SQUID magnetometers 921 3. Establishment of a fully penetrated flux distribution 922 4. Complex demagnetizing fields and anisotropy of high-temperature-superconductor crystal platelets 922 5. Complexities of the remanent state 923 6. Determination of the irreversible component of the magnetization 923 7. Step-by-step procedure for measurements of magnetic relaxation 924 B. Summary of experimental results 925 1. Temperature dependence 925 2. Field dependence 927 3. Deviations from time-logarithmic relaxation 928 4. Magnetic relaxation over surface barriers 929 5. Memory effect 930 6. V-I curves 930 7. Experimental determination of U(J) 931 C. Suppression of magnetic relaxation 932 1. Modulation of flux profiles and flux annealing 932 2. Effect of introducing defects 933 IV. Theoretical Approaches to Magnetic Relaxation in High-Temperature Superconductors 934 A. The electrodynamic equation of flux creep 935 B. Linear U(J)-the Anderson and Kim model 936 C. Nonlinear U(J) 937 1. Collective-creep theory 938 2. Logarithmic barrier 939 3. Barrier distribution 939 V. Concluding Remarks 940 Acknowledgments 941 References 941

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Statics and dynamics of the vortex state in type II superconductors

Sengupta¹,

Shi²

1995

High-Temperature Superconducting Materials Science and Engineering

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Evidence for nonlinear flux diffusion from magnetization relaxation in Bi2Sr2CaCu2O8 single crystals

Cited by 6 publications

References 32 publications

The flux-line lattice in superconductors

The flux-line lattice in superconductors

Magnetic relaxation in high-temperature superconductors

Statics and dynamics of the vortex state in type II superconductors

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