A reappraisal of irreversible behaviour in the intermediate state of a type-I superconductor
01 Oct 1990-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 170, Iss: 5, pp 431-436
TL;DR: In this article, the octupole moment of the intermediate state of superconductors was identified in the magnetization measurements on a disc-shaped Pb specimen and a quasi-irreversibility temperature was found in the data on a Pb disc.
Abstract: The nonequilibrium behaviour of the intermediate state of non-ellipsoidal specimens of type-I superconductors is well documented. We present the identification of a signal due to an octupole moment of this intermediate state in the magnetization measurements on a disc shaped Pb specimen. We can also identify a quasi-irreversibility temperature, like the HTSC materials, in the magnetization data on a Pb disc. However, its precise value at a given H depends on the orientation of the plane of the disc with respect to the applied field and it cannot be treated as a material characteristics of Pb.
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TL;DR: In this article, the authors describe the properties of the triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and also by thermal fluctuations.
Abstract: Magnetic flux can penetrate a type-II superconductor in the form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons) each carrying a quantum of magnetic flux phi 0=h/2e. These tiny vortices of supercurrent tend to arrange themselves in a triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-Tc superconductors (HTSCs) 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 HTSCs the FLL is very soft mainly because of the large magnetic penetration depth lambda . The shear modulus of the FLL is c66~1/ lambda 2, and the tilt modulus c44(k)~(1+k2 lambda 2)-1 is dispersive and becomes very small for short distortion wavelengths 2 pi /k<< lambda . This softness is enhanced further by the pronounced anisotropy and layered structure of HTSCs, 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 ofthe two-dimensional `pancake vortices` in the layers. Various phase transitions are predicted for the FLL in layered HTSCs. Although large pinning forces and high critical currents have been achieved, the small depinning energy so far prevents the application of HTSCs as conductors at high temperatures except in cases when the applied current and the surrounding magnetic field are small.
866 citations
TL;DR: In this article, the authors describe the properties of the triangular flux-line lattice (FLL), which is more or less perturbed by material inhomogeneities that pin the flux lines and also by thermal fluctuations.
Abstract: Magnetic flux can penetrate a type-II superconductor in form of Abrikosov vortices. These 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-$T_c$ supercon- ductors (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: The shear modulus of the FLL is thus small and the tilt modulus is dispersive and becomes very small for short distortion wavelength. This softness of the FLL 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 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 2D pancake vortices in the layers. Various phase transitions are predicted for the FLL in layered HTSC's. The linear and nonlinear magnetic response of HTSC's gives rise to interesting effects which strongly depend on the geometry of the experiment.
812 citations
TL;DR: A review of magnetic irreversibilities in both conventional and high temperature superconductors can be found in this paper, where a review of recent studies on flux-creep and thermally-activated relaxation is presented.
Abstract: Magnetic measurements in the superconducting state of the high temperature superconductors have been characterized by the feature of irreversibility. Similar effects have been known in the conventional type II superconductors for about three decades now, and have been studied in great detail during the last few years. Recent studies of magnetic irreversibilities, in both conventional and high temperature superconductors, will be reviewed here. Thermally-activated relaxation accompanies such irreversibilities, and studies on flux-creep will also be reviewed.
19 citations
TL;DR: In this article, the authors quantitatively analyzed how the voltage induced in a pick-up coil is related to arbitrarily (i.e. non-uniformly) magnetized samples, arbitrarily large vibration amplitude and arbitrary direction of vibration.
Abstract: It is quantitatively analysed how the voltage induced in a pick-up coil is related to arbitrarily (i.e. non-uniformly) magnetized samples, arbitrarily large vibration amplitude and arbitrary direction of vibration. The influence of errors in the position and in the vibration direction of the sample on the measured magnetization is discussed, and a well known criterion, commonly used to minimize sample position errors, is generalized. The authors propose compensated coil pairs, which are insensitive to either spurious vibrations or to power line pick-up. They also outline a system which realizes a true vector measurement of the three dipole moments as well as a measurement of three of the five quadrupole moments.
17 citations
TL;DR: In this article, the irreversibility (T r, H r ) line via DC and AC magnetization techniques in a few specimens of lead (type I) and niobium (type II) was determined by four different methods, viz., (i) the merger of zero-field-cooled and fieldcooled magnetization curves, (ii) the vanishing of hysteresis in isothermal, DC magnetization, (iii) the appearance of a differential paramagnetic effect (DPE) in the in-phase AC susceptibility χ ′ H (T
Abstract: In our continuing efforts to look for the behavioural similarities between the specimen of high-temperature and conventional superconductors, we have searched for the irreversibility ( T r , H r ) line via DC and AC magnetization techniques in a few specimens of lead (type-I) and niobium (type-II). A comparison has been made of T r and H r values determined by four different methods, viz., (i) the merger of zero-field-cooled and field-cooled magnetization curves, (ii) the vanishing of hysteresis in isothermal, DC magnetization, (iii) the appearance of a differential paramagnetic effect (DPE) in the in-phase AC susceptibility χ ′ H ( T ) measured in DC field, and (iv) the peak in the out-of-phase AC susceptibility χ ″ H ( T ). The first method gives a lower limit of T r ( H ) values whereas the second method appears to give H r ( T ) values smaller than those evident from isothermal χ ′ H data. The identification of peak temperature in χ ″ H ( T ) data with T r ( H ) value is appropriate only if the contribution from the normal state electrodynamics can be isolated and the peaks in χ ″ H ( T ) is narrow. The observation of DPE in χ ′ H ( T ) data is qualitative feature whose presence is adequate to imply reversibility in magnetization response. However, its efficacy to locate very precisely the T r and H r values remains to be established.
11 citations
References
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Book•
11 Jan 2001
TL;DR: The first edition of this book provided an introduction to the many static and dynamic features of magnetic flux structures in what are now called classical or low-temperature superconductors.
Abstract: The first edition of this book provided an introduction to the many static and dynamic features of magnetic flux structures in what are now called classical or low-temperature superconductors. It went out of print not long after the discovery of high-temperature superconductors in 1986 by J.G. Bednorz and K.A. Miiller, a discovery which resulted worldwide in an explosive growth of research and development in the field of superconductivity. Because of this upsurge of activities, a strong demand for this book clearly continued. Since the contents of the fourteen chapters of the first edition are still valid and continue to represent a useful introduction into the various subjects, it was felt that a reprinting of these chapters in this second edition would be highly attractive. In this way, the reader is also able to trace the earlier scienti- fic developments, themselves constituting important ideas sometimes forgot- ten by the new community dealing with high-temperature superconductivity. However, because of the exciting and important recent progress in the field of high-temperature superconductivity, an extensive chapter has been added in this second edition. It provides a summary of the new developments and a discussion of the highlights. Here keywords such as vortex matter, vortex imaging, and half-integer magnetic flux quanta describe surprising new issues.
497 citations
403 citations
79 citations
TL;DR: In this paper, a single crystal of Bi2Sr2CaCu2O8 (Tc similar 84 K) has been exposed to fast neutron irradiation up to a fluence of 6 1017 cm−2 (E > 0.1 MeV).
Abstract: A single crystal of Bi2Sr2CaCu2O8 (Tc similar 84 K) has been exposed to fast neutron irradiation up to a fluence of 6 1017 cm−2 (E > 0.1 MeV). D.c. magnetization measurements made prior to and following irradiation show significant enhancements of irreversibility in the magnetization loops and a shift of the "irreversibility" line to much higher fields and temperatures. This provides evidence for the absence of phase transitions in the flux line lattice and the predominance of depinning phenomena at high fields and temperatures.
61 citations
TL;DR: In this article, the magnetic behavior of cylindrical superconductors in transverse magnetic fields is developed for Landau's branching laminar model of the intermediate state, and for a branching thread model.
Abstract: The magnetic behaviour of cylindrical superconductors in transverse magnetic fields is developed for Landau's branching laminar model of the intermediate state, and for a branching thread model. The main features of the magnetization and resistance curves presented in parts I and II receive qualitative explanation, and expressions are derived for quantitative comparison of experiment with theory.
24 citations