P. Haibach

Structural and electrical characterization of SrBi2Nb2O9 thin films deposited on YBa2Cu3O7−δ and Nb doped SrTiO3

We have investigated the crystal structure and the ferroelectric properties of SrBi2Nb2O9 (SBN) thin films with YBa2Cu3O7−δ (YBCO) as the bottom and Au as the top electrode. Epitaxial heterostructures of YBCO and SBN were prepared by dc and rf sputtering, respectively, on SrTiO3 substrates. In a second layout we used a semiconducting Nb doped (0.05 wt % Nb) SrTiO3 (N-STO) substrate as the bottom electrode. The crystal structure of the films was characterized by x-ray diffraction. Since the SBN films exhibit a perfect c-axis oriented growth without the (115) phase the hysteresis loop measurements do not indicate ferroelectric behavior of the SBN films. The diode with a N-STO bottom electrode reveals, for a positive and negative applied voltage, a depletion and accumulation of the carrier density, respectively. The time dependent polarization and depolarization current can be described by a power law (Curie-von Schweidler). The conductivity as a function of applied voltage can be explained by the Schottky e...

MgO surface microstructure and crystalline coherence of Co/Pt superlattices

We report the growth of Co/Pt(111) superlattices sputtered onto MgO(111) substrates of different surface quality. Long-range structural coherence in the Pt-seed layers and the superlattices could only be obtained on specially re-polished substrates. In seed layers and superlattices grown on miscut re-polished substrates suppression of abc versus acb stacking was observed.

Absence of correlated flux pinning by columnar defects in irradiated epitaxial Bi2Sr2CaCu2O8 thin films

Abstract Using heavy-ion irradiation, we produced columnar defects of different density and orientation in epitaxial Bi 2 Sr 2 CaCu 2 O 8 thin films. Although this increases the normal state resistivity and the critical temperature is reduced proportionally to the volume fraction of damaged material, pinning-related quantities like critical current density, activation energy and depinning field are enhanced in external magnetic fields. Transport measurements in dependence of the magnetic field and its orientation consistently indicate two-dimensional pinning of pancake vortices at the columnar defects. We observe the absence of correlated flux pinning by columnar defects and compare to heavy-ion-irradiated single crystals and tapes, where line-like correlations have been observed.

Preparation and x-ray pole-figure characterization of DC-sputtered Bi-2201, Bi-2212 and Bi-2223 thin films

Thin films of the three members of the superconducting series , n = 1,2,3, were prepared by diode sputtering. X-ray characterization shows that all the films are single phase and c-axis oriented and in addition they are epitaxially grown. The latter is found by x-ray pole-figure measurements taken with a four-circle diffractometer. These are emphasized in this work. AC susceptibility measurements show that, while the 2201 films are not superconducting until 4 K, the transition temperatures of the 2212 films are 82 K - 90 K and of the 2223 films 84 K - 89 K.

Tunneling into epitaxial UPd2Al3 thin films

Abstract UPd 2 Al 3 –AlO x –Pb Giaever-type tunneling junctions were prepared employing an in vacuo process. The high junction quality is evident by the observation of the well-known superconducting density of states of the Pb counter electrode. For H Pb c2 H ≪ H UPd 2 Al 3 c2 an energy gap for UPd 2 Al 3 along the c -axis is well-resolved. This represents the first direct observation of the superconducting density of states of a heavy-fermion-compound by spectroscopic means.

Transversal thermovoltages of (1 1 9) Bi2Sr2CaCu2O8+δ thin films on vicinal (1 1 0) SrTiO3 substrates

Abstract Biaxial textured (1 1 9) oriented Bi 2 Sr 2 CaCu 2 O 8+δ thin films were fabricated by DC-Magnetron sputtering on vicinal (1 1 0) SrTiO 3 substrates. The crystal orientation and stochiometry of the films were obtained from precise X-ray diffraction measurements in four-circle geometry. According to anisotropic transport measurements, the superconducting transition temperature is approximately 47 K and the normal state resistivities along two perpendicular paths differ by a factor of 13.5. Transversal thermoelectric effects were investigated by measuring thermovoltages transverse to temperature gradients parallel to the surface normal induced by pulsed laser irradiation. At room temperature and energy densities of 15 mJ/cm 2 thermovoltages up to 355 mV were obtained.

Vortex dynamics in Bi2Sr2CaCu2O8-thin films in the presence of columnar defects

AbstractWith heavy ion irradiation we create continous amorphous columnar defects in Bi2Sr2CaCu2O8-thin films. With regard to a reliable comparison of irradiation effects three of four identical striplines on the same samples were exposed to different irradiation procedures. We performed irradiations as well parallel as under different angles with respect to the film

Magnetotransport properties of epitaxial (1 0 0)- and (1 1 1)-oriented CeSb thin films

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