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IEEE The current-carrying ability of type II superconductors can be effectively enhanced by introducing certain intelligent defects within the material. These defects can also give rise to other practically and scientifically appealing effects, such as current rectification, flux quantum filtering, and inhomogeneous response to external magnetic field and applied current. One such intelligent defect, which can be artificially fabricated in a controlled manner, is the removal of the superconductor in periodic regions throughout the sample, known as an antidot. In this paper, large scale antidots of the order of 2-3 & #x03BC;m were used in different shapes to discover potentially novel effects due to differing pinning potentials. Different shapes had varying responses to the critical current, some of which enhanced the flux pinning capacity. Large scale antidots were also used to create a ratchet effect by utilising the orientation of triangles in two different samples to pin vortices in unbalanced fashion depending on applied current/magnetic field direction.

A novel mathematical approach has been developed to complete the inversion of the Biot-Savart law in one- and two-dimensional cases from measurements of the perpendicular component of the magnetic field using the well-developed Magneto-Optical Imaging technique. Our approach, especially in the 2D case, is provided in great detail to allow a straightforward implementation as opposed to those found in the literature. Our new approach also refines our previous results for the 1D case [Johansen et al., Phys. Rev. B 54, 16264 (1996)], and streamlines the method developed by Jooss et al. [Physica C 299, 215 (1998)] deemed as the most accurate if compared to that of Roth et al. [J. Appl. Phys. 65, 361 (1989)]. We also verify and streamline the iterative technique, which was developed following Laviano et al. [Supercond. Sci. Technol. 16, 71 (2002)] to account for in-plane magnetic fields caused by the bending of the applied magnetic field due to the demagnetising effect. After testing on magneto-optical images of a high quality YBa 2 Cu 3 O 7 superconducting thin film, we show that the procedure employed is effective.

In this paper the origin of flux-jumps in Nb thin films is established during magnetization measurements using a vibrating sample magnetometer (VSM). Magnetization measurements of the flux avalanche activity show its strong dependence on frequency and amplitude of VSM vibration. In particular, under certain conditions the vibrations induce a transition from a stable superconducting critical state to an undercritical state, accompanied by the 20-fold drop in the magnetic moment. These features allow the elucidation of the origin of the flux-jumps. In contrast to the commonly assumed thermomagnetic instabilities to be responsible for the flux-jumps in Nb films, our results provide solid support for an alternative explanation being due to criticality-built instability well represented by a sandpile. Considering properties of the flux-flow during a flux avalanche regime allows us to estimate nonuniformity of a magnetic field in a VSM sample space developed as a result of vibrations.

IEEE The effects of the additions of powdered titanium carbide (TiC) and polyvalent titanium oxides (Ti-O) to MgB2 (synthesized under high pressure (2 GPa)-high temperature (800 and 1050 & #x00B0;C) conditions) on the critical current density, jc, critical magnetic fields, BC2 and Birr, and the related transformations in the materials structures are reported. The superconducting characteristics are compared with that of MgB2 with titanium (Ti) additions synthesized under the same conditions. The synthesis temperature, the ability of Ti-containing compounds to act as a getter, and the different diffusion rates of Mg and B into grains of these additions influence the distribution of the elements (boron, magnesium and impurity oxygen) in the structures of MgB2-based materials. This in turn affects the formation of pinning centers, the resulting flux pinning and eventually the superconducting properties (jc, BC2, Birr).

Magnetic particles can be used to take advantage of both defect and magnetic pinning in high-temperature superconductors. We combined layers of ferrite+cerium oxide with YBCO to see their effect both on the structure of the YBCO and on flux pinning. The deposition temperature of the ferrite greatly affects its structure and also the saturation magnetization. Combined with YBCO, the magnetic layer distorts the structure of YBCO, although, for example, the critical temperature remains rather unchanged. According to the structural results achieved here, the magnetic pinning layer is best positioned on the top of YBCO. This way, an improvement in Jc(B) is seen in all the field range, and also, a clear improvement of the accommodation field was measured. However, it does not play a huge role whether the ferrite is CoFe2O4, NiFe2O4, or ZnFe2O4, all mixed with CeO2.

We present a novel method for analysis of superconducting thin films using dynamic magneto-optical imaging, revealing hallmarks of flux penetration with temporal resolution around 1 ms (in the present work) or better. This method involves investigation of transient field and dynamic current distributions, which are calculated by an inversion procedure on the Biot-Savart Law, which we show to be valid under dynamic conditions. We compare and discuss the flux front penetration speed and evolution of current distribution in high quality YBa2Cu3O${}_{7-\delta }$ thin films with that of samples deliberately damaged in such a way as to reduce critical current density without causing macroscopic damage.

In this work the effect of vibrations on critical current density ( Jc) of superconductors has been studied. The vibrations are shown to affect Jc of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency ( f ) and/or amplitude (A) leads to progressive reduction of Jc as a function of magnetic field (Ba). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on Jc (Ba) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending Ba is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field (Birr) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of Birr for Jc modeling is demonstrated.

Superconducting Magnetic Energy Storage (SMES) systems have theoretically been considered for model applications in a potentially compact and practical form for domestic sustainable power. Using two different models, we have compared two different types of superconducting solenoids for this purpose. The optimal performance of helically wound solenoids of NbTi (or MgB2) wires are compared with that of pancake solenoids of the YBCO tape. The maximum energy storage of the coils has been obtained for various parameters and dimensions by optimizing core radius, coil length, and magnetic field strength. Helical solenoids made from NbTi wires are shown to somewhat outperform pancake coils made of YBCO-coated conductors. However, this consideration is, respectively, made at operation temperatures of 4.2 and 77 K. The viability of such compact SMES for "domestic" (or some "exotic") sustainable energy systems is discussed.

The glass-like vortex distribution in pulsed laser deposited YBa2Cu3O7 − x thin films is observed by scanning superconducting quantum interference device microscopy and analysed for ordering after cooling in magnetic fields significantly smaller than the Earth's field. Autocorrelation calculations on this distribution show a weak short-range positional order, while Delaunay triangulation shows a near-complete lack of orientational order. The distribution of these vortices is finally characterised as an isotropic vortex glass. Abnormally closely spaced groups of vortices, which are statistically unlikely to occur, are observed above a threshold magnetic field. The origin of these groups is discussed, but will require further investigation.

The influence of laser frequency on the structure and physical properties of thin films grown by pulsed laser deposition has been studied. Different types of thin films, hard ferromagnetic FePt L10 and quasi-single crystal superconducting YBa2Cu3O7 (YBCO), have been used for demonstration of the effect. Significant structural modifications have been obtained for the films with similar thicknesses. These modifications are shown to dramatically control their corresponding properties, providing an instrumental ability for tuning the practical characteristics of the films by changing the laser frequency of their deposition. In particular, 20-fold increase of coercive field and modification of demagnetization mechanism are obtained for FePt films by varying the frequency from 1 Hz to 6 Hz. Over a similar frequency range, a strong dependence on the laser frequency is discovered for the YBCO films for the critical current density behavior as a function of the applied magnetic field [Jc(Ba)] with the unexpected reversal of Jc(Ba) curves with temperature. The mechanisms of structure modifications and corresponding property variations are proposed.

Superlattices formed of two antagonic characteristics have been broadly studied in literature mainly in order to clarify the effects of proximity and interface interactions. Here, we present a study of superlattice introducing an insulator between each superconducting and ferromagnetic layer. The electrical insulator STO, YBCO and LCMO layer are deposited by PLD method. The samples with STO show more intergrowth surface morphology, which favors the application providing better contacts between the grains. The magnetic measurements indicated higher Tc values and high anisotropy for SLs with STO, which is dependent on the relative thickness of LCMO and YBCO.