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Influences of cracking of coating layer under applied tensile strain on V(voltage)-I(current) curve, critical current, and n-value of DyBa2Cu3O7-δ coated conductor were studied experimentally and analytically. The experimentally measured variations in V-I curve, critical current, and n-value with increasing applied strain and the correlation of n-value to critical current were described well by the partial crack-current shunting model of Fang et al. Also, the variations in the ratio of shunting current to overall critical current and the ratio of voltage developed in the cracked region to overall voltage with extension of crack, and the variation in critical current with the ratio of noncracked area to overall cross-sectional area of superconducting layer were revealed. [ABSTRACT FROM AUTHOR]

The author calculates precisely the induced currents in striated YBa2Cu3O7 coated conductors covered partially by segmented pieces of normal metal, connecting the individual superconducting stripes. It is shown that the induced current density is below the critical current density of the superconducting stripes and the coupling losses are acceptable low, ensuring in addition sufficient current sharing between the stripes. Thus, the proposed structure can be applicable at ac conditions without twisting procedure. The ratio of the current closed between the normal plates to the current flowing in the superconducting stripes and the losses in the substrate are also discussed. The total current flowing through the whole length of the superconductor, which has to be closed at the ends, is also acceptable low. In addition, the frequency range, in which the magnetic flux can fully penetrate both between the stripes and into the normal segments, is given. [ABSTRACT FROM AUTHOR]

[100]-tilt grain boundary Josephson junctions with misorientation of the c-axis directions have been fabricated using epitaxial (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re)-1212] thin films grown on SrTiO3 bicrystal substrates. Two types of the [100]-tilt junctions, that is, the mountain-type junction and the valley-type junction, of which a-b planes formed a mountain shape and a valley shape along the grain boundaries, respectively, were examined for various misorientation angles (θ). Both the types of junctions showed resistively shunted junction-type current-voltage (I-V) characteristics with relatively high characteristic voltages in a wide temperature range from 4.2 to 110 K. The valley-type junctions exhibited properties superior to those for the mountain-type junctions, such as very low excess current and much homogeneous current distribution, which is attributed to different film growth mode near the grain boundaries. They also exhibited the products of the critical current (Ic) and the normal-state resistance (Rn) as high as 3.0–4.2, 1.0–1.4, and 0.2–0.4 mV at 4.2, 77, and 100 K, respectively. The misorientation angle dependences of junction parameters for the [100]-tilt junctions were compared with those for conventional [001]-tilt junctions with misorientation of the a-b plane directions. The Rn and the IcRn products for the [100]-tilt junctions were substantially larger than those for the [001]-tilt junctions. Large hysteresis in the magnetic-field dependence of Ic was observed for the applied field larger than a certain threshold value, suggesting flux penetration between the CuO2 planes. [ABSTRACT FROM AUTHOR]

An as-grown MgB2 crystalline thin film was fabricated at a low temperature of 270°C on an in-plane-lattice near-matched TiZr buffer layer grown on a sapphire Al2O3 (0001) surface. The critical temperature and the superconductivity critical current density of MgB2/TiZr/Al2O3 were found to be high compared with those of MgB2/Al2O3. The film was characterized by using synchrotron x-ray diffraction. The epitaxial relationship in the plane was MgB2[0110]//TiZr[0110]// sapphire [1120]. In-plane-lattice spacings, d//MgB2, d//TiZr, and d//sapphire obtained were 0.268, 0.258, and 0.239 nm for the MgB2(0110), TiZr(0110), and sapphire (1120) planes, respectively. [ABSTRACT FROM AUTHOR]

The spin-polarized current injection (SPCI) experiments, where the spin-polarized current (IS) is injected into a 25 μm wide superconducting NbN bridge from a ferromagnetic Co2MnSi layer by tunneling through MgO barrier, show a large (≈67%) suppression of superconducting critical current (IC) due to IS injection at T/TC ≈ 0.4. This corresponds to a large dynamic gain of ≈36 at 3 K, which is 40 times higher than the gain at 6.5 K. Such a rapid rise of gain at lower temperatures strongly suggests a dominant role of SPCI in IC suppression as compared to the effect of Joule-heating. [ABSTRACT FROM AUTHOR]

We analyze the influence of the magnetic field generated by the supercurrents (self-field) on the current density distribution by numerical simulations. The thickness of the superconducting film determines the self-field and consequently the critical current density at zero applied field. We find an equation, which derives the thickness dependence of the critical current density from its dependence on the magnetic induction. Solutions of the equation reproduce numerical simulations to great accuracy, thus enabling a quantification of the dependence of the self-field critical current density with increasing film thickness. This result is technologically relevant for the development of coated conductors with thicker superconducting layers. [ABSTRACT FROM AUTHOR]

We report on spin dynamics of single magnetic antivortices driven by sudden excitation of a spin-polarized direct current. Using micromagnetic simulations, we find that there is a critical current density where spin dynamics transition occurs. Above the critical value, the core is switched on a time scale of ∼200 ps through two Bloch points injection after fully suppressed by a quadruple-vortices array, not through the well-known process involving an antivortex-vortex pair creation and annihilation. As the current density decreases, the time required to switch the core increases. The state after full relaxation depends on the current density (the excitation parameter). [ABSTRACT FROM AUTHOR]

A composite free layer (CFL) consisting of a soft layer and a hard layer exchange coupled in parallel is proposed. The experimental results showed that the critical current density (Jc) can be reduced from 7.05×106 A/cm2 of strong coupled CoFeB(12.5 Å)/Ru(4 Å)/NiFe(17.5 Å) CFL to 2.65×106 A/cm2 of weak coupled CoFeB(12.5 Å)/Ru(15 Å)/NiFe(17.5 Å) CFL. The macrospin simulations showed that the soft layer of CFL can assist the hard layer of CFL to switch at a lower Jc. These results suggest that by using CFL, it is possible to reduce the Jc of spin torque transfer switching without compromising the thermal stability. [ABSTRACT FROM AUTHOR]

In this work, we report on significantly enhanced critical current density (Jc) in MgB2 superconductor that was easily obtained by doping with a hydrocarbon, highly active pyrene (C16H10), and using a sintering temperature as low as ∼600 °C. The processing advantages of the C16H10 additive include production of a highly active carbon (C) source, an increased level of disorder, and the introduction of small grain size, resulting in enhancement of Jc. [ABSTRACT FROM AUTHOR]

A simple analytical expression is presented for hysteretic ac loss Q of a superconducting strip simultaneously exposed to an ac transport current I0 cos ωt and a phase-different ac magnetic field H0 cos(ωt+θ0). On the basis of the critical state model, the authors calculate Q for small current amplitude I0≤Ic, for small magnetic field amplitude H0≤Ic/2πa, and for arbitrary phase difference θ0, where Ic is the critical current and 2a is the width of the strip. The resulting expression for Q=Q(I0,H0,θ0) is a simple biquadratic function of both I0 and H0, and Q becomes maximum (minimum) when θ0=0 or π (θ0=π/2) [ABSTRACT FROM AUTHOR]

The superconducting grain-boundary (GB) network of coated conductors (CCs) is usually assumed to be a replica of the substrate network. In this letter, we analyze IBAD and RABITS CCs, where such replica either do or do not exist. We have analyzed the effect of GB overgrowth on the critical currents by quantifying the average superconducting grain size and determining the intragrain and grain-boundary critical current densities, JcG and JcGB. We have employed a recently developed inductive methodology enabling the simultaneous determination of these three parameters. We show that the percolative JcGB may be reduced by 50% if the GB networks do not correlate, while JcG and the grain pinning properties appear unaffected. [ABSTRACT FROM AUTHOR]

Switching of superconducting thin-film resistive fault-current limiting devices with alloy shunt layers was studied. Au–Ag alloy thin films, whose room-temperature resistivity is about six times higher than that of pure gold, were sputter deposited on YBa2Cu3O7 films on sapphire substrates with high critical current density of Jc=3.05±0.05 MA/cm2. A small sample, 5 mm wide and 40 mm long, had the capacity of a rated current of 32 Arms in normal operation and withstood a high voltage of 107 Vrms for 0.1 s after switching, resulting in a very high switching power density of ∼1.7 kVA/cm2, which is more than four times higher than conventional devices using gold shunt layers. [ABSTRACT FROM AUTHOR]

In a recent letter, Cao et al. [Appl. Phys. Lett. 88, 251116 (2006)] reported the growth of In+N codoped p-type ZnO films with a low resistivity of 1.58×10-1 Ω cm by a simple sol-gel spin coating method. Unfortunately, this low resistivity value is doubtful based on Hall effect measurement analysis. If the values of carrier concentration and Hall mobility are correct in their experiment, the resistivity value should be 10.62 Ω cm, but not 1.58×10-1 Ω cm. [ABSTRACT FROM AUTHOR]