Magnetic Properties Of Superconductors Research Articles

Fabrication and magnetic properties of SiO2 nanoparticles-doped BSCCO superconducting nanofibers by solution blow spinning

In this work, the magnetic properties of Bi2Sr2CaCu2O8+θ (BSCCO) superconducting nanofibers prepared by solution blow spinning technology were studied systematically. The BSCCO superconductors were doped with SiO2 nanoparticles in order to study the influence of non-superconducting impurities on the microstructure and magnetic properties of superconductors. The results showed that 0.2 wt% SiO2 nanoparticles can improve superconducting performance as efficient magnetic flux pinning centers in BSCCO superconductors. For examples the superconducting transition temperature was increased from 76.5 K to 80.3 K, the critical current density was increased from 0.68 × 108 A m−2 to 1.43 × 108 A m−2, and the pinning strength was increased from 4.4 × 107 N m−3 to 8.1 × 107 N m−3. In addition, it was found that appropriate amount of SiO2 nanoparticles can improve the size of superconducting grains and enhance the connectivity of superconducting grains. Moreover, the pinning mechanism of each sample demonstrated that SiO2 nanoparticles improved the pinning performance of BSCCO. Furthermore, this is the first report on the BSCCO superconductors that doped with SiO2 nanoparticles.

Structural and magnetic properties of superconductor NiBi3/α-Bi2O3 synthesized by mechanical alloying

A nanostructured NiBi3/α-Bi2O3 superconductor composite has been synthesized by the process of mechanical alloying through 19 h of high energy ball milling. The kinetics of formation is analyzed in detail by x-ray diffraction and the Rietveld method. A simple method is proposed to determine the crystallinity of the resulting sample by using the background Rietveld fitting that permits a quantitative analysis of the diffuse x-ray profile taking into account the air and Compton scattering. The diffuse scattering is attributed to the formation of a nanocluster of α-Bi2O3 which is confirmed by high-resolution transmission electron microscopy and Raman measurements. The magnetic measurements show superconducting transition at around 4 K and the existence of NiBi3/α-Bi2O3 nanophases with a low irreversibility field at around 1.01 T at 2 K. Analysis of magnetic susceptibility and isothermal magnetic hysteresis of the NiBi3/α-Bi2O3 nanocomposite indicates the simultaneous existence of bulk superconductivity and ferromagnetism below 4 K.

Conducting a Survey of Research on High Temperature Superconducting Transformers

Given the unique electrical and magnetic properties of superconductors, high temperature superconducting (HTS) transformers will play a central role in the electricity industry in the future. Therefore, identification and analysis of this type of transformers seems necessary and indispensable. To date, many types of development plans for HTS transformers have been carried out by major power companies and important research institutes, and it is expected that this type of transformers will become one of the superconducting power equipments installed at the first stage of commercialization in the power system. However, a review of reports and papers published in this field shows that there is still much work to be done to improve the design and performance of these transformers. This article presented a review classified by subject of previous research to help orient future research into the design, analysis, and manufacturing of this type of transformers.

The Path to Type-II Superconductivity

Following the discovery of superconductivity by Heike Kamerlingh Onnes in 1911, research concentrated on the electric conductivity of the materials investigated. Then, it was Max von Laue who in the early 1930s turned his attention to the magnetic properties of superconductors, such as their demagnetizing effects in a weak magnetic field. As a consultant at the Physikalisch-Technische Reichsanstalt in Berlin, von Laue was in close contact with Walther Meissner at the Reichsanstalt. In 1933, Meisner together with Robert Ochsenfeld discovered the perfect diamagnetism of superconductors (Meissner–Ochsenfeld effect). This was a turning point, indicating that superconductivity represents a thermodynamic equilibrium state and leading to the London theory and the Ginzburg–Landau theory. In the early 1950s in Moscow, Nikolay Zavaritzkii carried out experiments on superconducting thin films. In the theoretical analysis of his experiments, he collaborated with Alexei A. Abrikosov and for the first time they considered the possibility that the coherence length ξ can be smaller than the magnetic penetration depth λ m . They called these materials the “second group”. Subsequently, Abrikosov discovered the famous Abrikosov vortex lattice and the superconducting mixed state. The important new field of type-II superconductivity was born.

Setup for studying nonlinear magnetic properties of high-temperature superconductors with the aid of magnetization harmonics

A setup for measuring cophasal and quadrature components of higher harmonics of an electromotive-force signal of the response of a high-temperature superconductor makes it possible to study nonlinear magnetic properties of superconductors in variable magnetic fields of up to 1 kOe and constant magnetic fields of up to 10 T in the temperature range of 5–300 K. This setup was used to measure the temperature dependences of the absolute values of the real and imaginary parts of the first and third harmonics of the magnetization of textured Yba2Cu3O7 − x polycrystalline samples in the temperature range of 77–220 K at various values of variable and constant magnetic fields. An analysis of resulting data made it possible to reveal the presence of different dynamical modes of the magnetic flux in YBa2Cu3O7 − x that were dominant in different temperature ranges. The nonlinearity of the magnetization of YBa2Cu3O7 − x (the appearance of higher harmonics) was observed up to temperatures in the range of T = 103–112 K, which were substantially higher than the temperature of the transition of this compound to a superconducting state. The observed feature in the magnetization of YBa2Cu3O7 − x was associated with the emergence of a pseudogap state in this compound.

Magnetic properties of deformed superconductors

This communication concerns the geometric effect on magnetic properties of superconductors. The metric description for quantum particles holds only in limited class of medium and the screw-dislocated medium is considered. When the Ginzburg–Landau equation with Maxwellʼs equations was solved based on this description, it was shown that self-adjointness of the operator is guaranteed by specified solutions. As a result, isolated vortex exists at dislocation line.

Simulation of the current dynamics in superconductors: Application to magnetometry measurements

A simple model for simulating the current dynamics and the magnetic properties of superconductors is presented. Short simulation times are achieved by solving the differential form of Maxwell's equations inside the sample, whereas integration is only required at the surface to meet the exact boundary conditions. The procedure reveals the time and position dependence of the current density and the magnetic induction $(B)$ making it very convenient to apply field dependent material parameters for the simulation of magnetization loops, relaxation measurements, etc. Two examples, which are important for standard magnetometry experiments, are discussed. First, we prove that evaluating the critical current density $({J}_{\text{c}})$ from experiment by applying Bean's model reveals almost the exact ${J}_{\text{c}}(B)$ behavior if the evaluation is corrected by a simple numerical expression. Second, we show that the superconducting volume fraction of a sample can be directly determined from magnetization loops by carefully comparing experiment and simulation in the field range, where the current loops are differently oriented within the sample.

Susceptibility of Superconductors via Scattering Approach

The measurement of magnetic properties of superconductors is usually understood in context with flux penetration length and in case of type-II superconductors also with vortex matter. We investigate the behavior of superconductors in very weak magnetic fields, typically μ0H < 1 μT, near the critical temperature. The aim is to explore the details of SN transition and phase diagram (B,T) of vortex matter in extreme type-II superconductors like cuprates. The data recorded on HTS, even if extensively challenged with theory, are hard to understand as a vortex matter behavior. On the other hand, interpretation on the basis of electron conductivity arising from electron scattering is consistent even with data obtained by x-ray diffraction, photoemission, tunnelling spectroscopy and specific heat.

Magnetic properties of superconductors with strong spin-orbit coupling

We study the response of a superconductor with a strong spin-orbit coupling on an external magnetic field. The Ginzburg-Landau free energy functional is derived microscopically for a general crystal structure, both with and without an inversion center, and for an arbitrary symmetry of the superconducting order parameter. As a by-product, we obtain the general expressions for the intrinsic magnetic moment of the Cooper pairs. It is shown that the Ginzburg-Landau gradient energy in a superconductor lacking inversion symmetry has unusual structure. The general formalism is illustrated using as an example CePt$_3$Si, which is the first known heavy-fermion superconductor without an inversion center.

Magneto-Optical Visualization of Magnetic Processes in Superconducting Strip With the Application of Magnetic Fields and Currents

The magneto-optical imaging (MOI) technique is widely employed to characterize the magnetic properties of superconductors and other magnetic materials because it can easily show the variation of flux density over a plane with relatively high resolution. In this paper, flux profiles visualized by the MOI technique will be presented for different experimental conditions. The sample investigated is a high-temperature superconducting single strip. Three cases are investigated: 1) application of external currents; 2) application of external magnetic fields; and 3) simultaneous application of external magnetic field and current. The behavior of complicated vortex penetration into the samples for different conditions will be discussed in detail. The magnetic flux profiles are calculated taking into account the sample thickness, as well as the interval between the sample and the MOI indicator film. The calculated and the experimental results are compared and discussed.

A Torsion Balance for Studying Anisotropic Magnetic Properties of Superconducting Materials

A low-temperature torsion balance for studying magnetic properties of superconductors is described. The device can operate in the modes of the rotation or vibration of an axisymmetric superconducting sample in an external magnetic field. The balance provides for the measurement of a torque τ of 10–8 –1 N·m applied to the sample. The device is highly sensitive to frozen magnetic fluxes even of the order of magnitude of the geomagnetic field (H ≤ 0.5 Oe). To eliminate the effect of frozen magnetic fluxes, two-layer Permalloy shields providing for the cooling of the sample in the field H < 10–3 Oe are used. The capabilities of the developed method for studying critical parameters and the anisotropic magnetic properties of superconductors are described.

Peak effect and giant flux jumps in hard superconductors: the problem of “islands” jumps on H-T diagram

Magnetic properties of superconductors with peak effect were investigated both experimentally and theoretically in frames of the critical state model which incorporates the flux jump instability criterion. Theoretical analyses show some “forbidden” band for flux jumps on the magnetic field axis. Features of H-T diagrams of instability of superconductors with peak effect are discussed.

Introduction to Superconducting Circuits

Preview. AC Properties and Superconducting Energy Gap. Magnetic Properties of Superconductors. Superconducting Materials and Thin--Film Technology. Josephson Devices. Superconducting Digital Circuits. Superconducting Radiation Detectors. Epilogue: Future Prospects for Superconducting Circuits. Bibliography. Appendices. Indexes.

Application of high-TCsuperconductors in electronics

Potential applications of high-temperature superconductors in electronics and communications are described with an emphasis on the relationship to the fundamental superconducting phenomena of zero resistance, magnetic-field expulsion and macroscopic quantum effects. The paper includes a description of the electric and magnetic properties of superconductors, potential microwave applications in filters, resonators, delay lines and superconducting transistors, and of mixers and other detectors. Simple logic circuits, an analogue-to-digital convertor and a SQUID magnetometer are also discussed, using the established conventional superconducting technology as reference point, and assessing the likely impact and importance of high-TC materials.

Phenomenological theory of unconventional superconductivity

This article is a review of recent developments in the phenomenological description of unconventional superconductivity. Starting with the BCS theory of superconductivity with anisotropic Cooper pairing, the authors explain the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional superconductivity. This is used to classify the possible superconducting states in a system with given crystal symmetry, including strong-coupling effects and spin-orbit interaction. On the basis of the BCS theory the unusual low-temperature properties and the (resonant) impurity scattering effects are discussed for superconductors with anisotropic pairing. Using the Ginzburg-Landau theory, the authors study several bulk properties of such superconductors: spontaneous lattice distortion, upper critical magnetic field, splitting of a phase transition due to uniaxial stress. Two possible mechanisms for ultrasound absorption are discussed: collective modes and damping by domain-wall motion. The boundary conditions for the Ginzburg-Landau theory are derived from a correlation function formulation and by group-theoretical methods. They are applied to a study of the Josephson and proximity effects if unconventional superconductors are involved there. The magnetic properties of superconductors that break time-reversal symmetry are analyzed. Examples of current and magnetic-field distributions close to inhomogeneities of the superconducting order parameter are given and their physical origin is discussed. Vortices in a superconductor with a multicomponent order parameter can exhibit various topological structures. As examples the authors show fractional vortices on domain walls and nonaxial vortices in the bulk. Furthermore, the problem of the possible coexistence of a superconducting and a magnetically ordered phase in an unconventional superconductor is analyzed. The combination of two order parameters that are almost degenerate in their critical temperature is considered with respect to the phase-transition behavior and effects on the lower and upper critical fields. Because heavy-fermion superconductors---which are possible realizations of unconventional superconductivity---have been the main motivation for the phenomenological studies presented here, the authors compare the theoretical results with the experimental facts and data. In particular, they emphasize the intriguing features of the compound U${\mathrm{Pt}}_{3}$ and consider in detail the alloy ${\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{Be}}_{13}$.

Measurement of Surface Magnetic Field of Superconductor by Magnetic Resonance

A technique for the measurement of the surface magnetic field by magnetic resonance is presented. Its application to copper oxide superconductors YBa2Cu3O7-x demonstrated that the magnetic properties of superconductors can be conveniently investigated by this technique.

Magnetic properties of superconductors with uniaxial symmetry

AbstractIn type‐II superconductors with uniaxial symmetry the three critical fields (Hc1, Hc2, Hc3) are calculated near the transition temperature Tc using the anisotropic Ginzburg‐Landau equations. It is shown that in general an induced magnetic field δH⊥ perpendicular to the applied magnetic field exists and that the anisotropy removes the degeneracy in the direction of the flux‐line lattice. The pattern and the orientataion of the flux‐line lattice are in good agreement with the experimental results of technetium.

Magnetic properties of superconductors studied by neutron depolarization

A new method is described which allows the study of the magnetic properties of superconductors. Measurements on various niobium and lead samples were taken to study the influence of surface conditions and lattice defects on the formation of the mixed and intermediate states. A strong dependence of flux penetration on surface conditions is found. AboveHC1 the results indicate the formation of a disturbed flux line lattice. The influence of external fields present when the superconductor is cooled throughTc is discussed and evidence for the intermediate state of type II superconductors is presented. Finally a simple model is used to evaluate the mean angle of deviation from the ideal lattice.

Magnetic Properties of Superconductors with Resonance Scattering

Magnetic Properties of Superconductors with Resonance Scattering

The Physical Principles of Magnetism

The Physical Principles of Magnetism