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An alternative method for determining the lock-in angle φL for pinning of the vortices on extended defects has been developed. This method does not require any preassumed criterion for defining φL. Highly twinned Sm1+xBa2-xCu3O6+y single crystal was used for demonstrating the method. Appropriate scaling of the hysteresis loops measured for different angles between the field and twin planes in highly twinned SmBaCuO single crystal led to a clear discrimination between two vortex dynamics regimes. From this scaling, the lock-in angle was determined to be 6°±0.1° for the single crystal investigated. This method significantly reduces the uncertainty in determining the lock-in angle when compared to all the other currently employed methods. [ABSTRACT FROM AUTHOR]

Magnetic measurements carried out on MgB2 superconducting round wires have shown that the critical current density Jc(Ba) in wires sheathed by iron can be significantly higher than that in the same bare (unsheathed) wires over a wide applied magnetic field Ba range. The magnetic behavior is, however, strongly dependent on the magnetic history of the sheathed wires, as well as on the wire orientation with respect to the direction of the applied field. The behavior observed can be explained by magnetic interaction between the soft magnetic sheath and superconducting core, which can result in a redistribution of supercurrents in the flux filled superconductor. A phenomenological model explaining the observed behavior is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dramatic structure variations of L10-FePt and superconducting YBCO thin films have been obtained by “simply” varying the laser frequency for pulsed laser deposition of these films, while keeping the thickness of the films constant. [•] The origins of structure variation with laser frequency for both Volmer-Weber mode grown FePt and Straski–Krastanov mode grown YBCO films are discussed and compared. [•] Deposition frequency increase from 1 to 6Hz leads to up to 20-fold enhancement of the coercive field in FePt films of constant thickness obtained by modification of demagnetization mechanism in laser frequency-varied structures (observed with MFM). [•] Varying growth kinetics of YBCO films by laser frequency leads to strong modification of dependence of critical current density on applied magnetic field (J c (B a )) with unexpected J c (B a ) reversal behavior with measurement temperature; such reversal behavior was never reported before; the mechanism of J c (B a ) modification is discussed. [ABSTRACT FROM AUTHOR]

The dependence of properties in YBa2Cu3O7 (YBCO) films grown by pulsed laser deposition at different distances from the target to a substrate has been systematically studied. The target to substrate distance DTS is shown to enable simple means for tunability of the critical current density and microstructure of the YBCO films. The variation of structural and electromagnetic properties in the films as a function of DTS has been explained in terms of laser plume propagation model and thin film formation mechanism. [ABSTRACT FROM AUTHOR]

MgB2 superconductors were made with two processes in this work. In one case, the SiC doped MgB2 pellets were sintered in excessive Mg medium. It is found that the samples sintered in excessive Mg medium present Mg-rich composition comparing with the one sintered in Ar gas. The density is higher and the resistance is lower due to the penetration of the Mg into the pores and grain boundary of MgB2, which is beneficial to the Jc improvement. In the other case, a two-step process was employed to make MgB2. Jc, of the sample with the composition of MgB4 is very low after the first sintering. The Jc. was dramatically improved after the second sintering, but J. of the two-step made sample is still poorer than the MgB2 made with general one step sintering due to the connectivity deterioration caused by the pulverization prior to the second sintering. [ABSTRACT FROM AUTHOR]

Magnetic field and temperature dependencies of the critical current density, J[sub c](Hc, T) were measured by SQUIDmagnetometry, ac magnetic susceptibility, and dc transport current techniques in the single-crystalline epitaxially-grown by offaxis dc magnetron sputtering YBa[sub 2]Cu[sub 3]O[sub 7-δ] (YBCO) films with J[sub c](Hc, 77 K) ≥ 2 · 10[sup 6] A/cm². The mechanism of vortex depinning from growth-induced linear defects, i.e., out-of-plane edge dislocations in low-angle tilt domain boundaries, is shown to describe quantitatively measured J[sub c](Hc, T). The developed model takes into account a statistical distribution of the dislocation domain boundaries ordered in a network as well as the interdislocation spacing within boundaries. Actual structural features of YBCO film known from HREM data turn out to be extracted from J[sub c](Hc, T)-curves by a fitting procedure within the proposed model. [ABSTRACT FROM AUTHOR]

A novel method is proposed to increase the MgB2 core density and, as a consequence, the critical current density of Fe-sheathed MgB2 wires. This method involves two additional stages compared to the usual wire fabrication: post-annealing mechanical deformation and a consecutive heat-treatment. Using this method we obtained denser core structures in 7-filament wire having Jc values larger by a factor of about 4.3 than that found in the initial “in situ” prepared mono-core wire. Independent of the manufacturing procedure, the wires showed a transport property degradation effect after being exposed to the air for 4 months. [Copyright &y& Elsevier]

Much smoother surfaces and significantly improved superconducting properties of relatively thick YBa2Cu3O7 (YBCO) films have been achieved by introducing a multilayered structure with alternating main YBCO and additional NdBCO layers. The surface of thick (1 μm) multilayers has almost no holes compared to YBCO films. Critical current density (Jc) has been drastically increased up to a factor >3 in 1 μm multilayered structures compared to YBCO films over entire temperature and applied magnetic field range. Moreover, Jc values measured in thick multilayers are even larger than in much thinner YBCO films. The Jc and surface improvement have been analyzed and attributed to growth conditions and corresponding structural peculiarities. [ABSTRACT FROM AUTHOR]