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The electric and magnetic properties of microbridges made from 440 nm thick Y–Ba–Cu–O films prepared on Al2O3 substrates with CeO2 sublayers by the pulsed injection metal organic chemical vapor deposition (MOCVD) method were studied in temperatures ranging from 20 K to 300 K in order to investigate the possibilities of using these microbridges as fast fault current limiters. The application of an external magnetic field () causes the flux flow induced magneto-resistive effect, which is proportional to and to at low and high temperatures, respectively. The experimentally obtained S-shaped I–V characteristic and the change of the microbridge resistance over time when affected by a step-like magnetic field can be well explained using a thermo-electrical model based on Joule heating and the flux flow nature of the resistive state (RS). The transition from the superconducting to the RS, studied using ns duration rectangular waveform electrical pulses able to create up to ≈2106 A cm−2 current densities without rises of microbridge temperatures, demonstrated that the I–V characteristics of the RSs consisting of an assembly of straight lines corresponding to the different pinning centers. At temperatures close to the critical temperature of superconductivity, the number of these lines increases, and the I–V characteristics can be described with high accuracy by a power law. It was concluded that microbridges made from these films can be used as protectors against complicated waveform electromagnetic pulses having short rise times, high voltage peak amplitudes and long low-value over-current 'tails'. [ABSTRACT FROM AUTHOR]

Phase switching in GeTe thin films (grown using a modified metal organic chemical vapor deposition system) upon pulsed femtosecond and nanosecond laser irradiation has been studied. Two in situ methods, i.e., optical microscopy and real-time reflectivity measurements, have been used in order to compare the optical response before and after phase change and to follow the phase change dynamics with a time resolution close to 400 ps. The results show that cycling is possible under irradiation with both fs and ns pulses using single pulses for amorphization and multiple pulses for crystallization. The use of ns pulses favors the crystalline-to-amorphous phase transformation, with a characteristic transformation time of ∼15 ns. The presence of the liquid phase was identified and temporally resolved, featuring a well-defined transient reflectivity state, in between those of the crystalline and amorphous phases. We have also studied the role of material configuration in the phase change dynamics and the mechanisms involved in the re-crystallization process. [ABSTRACT FROM AUTHOR]

Phase changes between amorphous and crystallized states were induced by laser irradiation with nanosecond pulses in GexTey films grown by metal organic chemical vapor deposition. The different phases were obtained by adjusting the pulse energy and could be distinguished by their different optical reflectivities. The corresponding structural changes were studied by Raman spectroscopy, showing marked differences for the two phases. A clear correlation is found between optical reflectivity levels, crystallographic state and the evolution of Ge–Ge, Te–Te, and Ge–Te Raman bands. [ABSTRACT FROM AUTHOR]

High quality epitaxial La1−xSrxMnO3 films were deposited by pulsed injection metal organic chemical vapor deposition, using as precursor materials metal-2,2,6,6-tetramethyl-3,5-heptandionates dissolved in monoglyme. The influence of various deposition conditions, substrate material and film thickness on film properties was investigated. The best films were deposited on LaAlO3 substrates at 825 °C: films exhibited a sharp semiconductor–metal transition and high magnetoresistance (∼40%) at a close-to-room temperature and in a rather low field of 1.5 T. In-situ or ex-situ high-temperature annealing in oxygen increased the temperature of semiconductor–metal transition, but decreased the magnetoresistance and the temperature coefficient of resistance. Biaxial strain imposed by the lattices’ mismatch was clearly observed in thinner La1−xSrxMnO3 films on perovskite substrates. Tensile strain was present in the films on SrTiO3 and compressive strain in the films on LaAlO3 (and less clearly on NdGaO3). Both tensile and compressive strains decreased the temperature of electric transition and the values of magnetoresistance. The strain was completely relaxed in the films more than ∼100 nm thick. [Copyright &y& Elsevier]

A mixed state in dc-biased thin films of II-type superconductors realizes the Abrikosov magnetic vortices/ antivortices, which are the result of the current-self magnetic field penetration into the film at temperatures lower than its critical temperature Tc. A nucleation of vortices/antivortices at the superconducting film's edges, their motion perpendicular to the direction of biasing current, and the annihilation in the film's center originates from a current dissipation in the superconductor and expresses itself in experiments as a dc voltage. This work reports on the results of simulation of current density in a 50 μm wide, 100 μm long, and 0.3 μm thick YBa2Cu3O7-x microbridges containing ¦-shaped 5 μm wide single channel of easy vortex motion fabricated by means of laser-writing technique. Analyzing a two-dimensional-net of resistors and assuming that, due to the Meissner-Ochsenfeld effect, the magnetic flux penetration into superconducting film is nonlinear, we demonstrate that presence of a ¦-shaped channel causes a non-homogeneous distribution of current in the microbridge. [ABSTRACT FROM AUTHOR]

A current-self-induced magnetic field Hj , such that Hc1 < Hj < Hc2 at T < Tc, penetrates a thin-film, type-II superconductor forming the Abrikosov magnetic vortex-antivortex pairs in the film's areas of weakest superconductivity. Our atomic force microscopy and scanning tunneling microscopy images confirm that in 50 μm wide, 100 μm long and 0.3 μm thick YBa2Cu3O7-x superconducting devices magnetic flux penetrates first into a 5 μm wide, ¦-shaped and partially deoxygenated (x ≈ 0:2) channel for easy vortex motion. When the Lorentz force overcomes pinning force in the channel, the flux starts to move and its drift dissipates energy inducing dc voltage. This work reports on the density of coherently moving vortices along the channel vs. temperature in range from 0:93Tc to 0:97Tc. Our simulations show that the vortex density vs. temperature dependence extracted from I-V measurements of our devices follows the temperature dependence of magnetic field penetration depth and the coherence length of the superconductor. [ABSTRACT FROM AUTHOR]

Vortex dynamics in laser-patterned channels for easy motion in YBa2Cu3O7-δ thin-film bridges has been investigated by electric transport and magneto-optical measurements. It has been found that the laser-writing technique, relying on selective deoxygenation of the illuminated areas of YBa2Cu3O7-δ films, enables manufacturing of channels with the decreased field of the first penetration and pinning strength. Current-induced vortices confined in such channels move coherently within a limited temperature and bias ranges. Coherence in vortex motion was confirmed by the direct observation of self-resonant, Josephson-like current steps on the bridge current-voltage characteristics. [ABSTRACT FROM AUTHOR]