Sign reversal of the Hall resistance in the mixed-state of La1.89Ce0.11CuO4 and La1.89Ce0.11(Cu0.99Co0.01)O4 thin films

in Physica C (2012), 479

The transport properties of La1.89Ce0.11CuO4(LCCO) and La1.89Ce0.11(Cu0.99Co0.01)O4 (LCCO:Co) superconducting thin films are investigated. When the external field H is applied along the crystallographic c ... [more ▼]

The transport properties of La1.89Ce0.11CuO4(LCCO) and La1.89Ce0.11(Cu0.99Co0.01)O4 (LCCO:Co) superconducting thin films are investigated. When the external field H is applied along the crystallographic c-axis, a double sign reversal of the Hall voltage in the mixed state of LCCO:Co thin films is observed whereas a single sign reversal is detected in LCCO. A double sign reversal of the Hall signal in LCCO can be recovered if the magnetic field is tilted away from the plane of the film. We find that the transition from one to two of the Hall sign reversal coincides with the change in the pinning from strong to weak. This temperature/field induced transition is caused either by the magnetic impurities in LCCO:Co or by the coupling between the pancake vortices and the in-plane Josephson vortices in LCCO. These results are in agreement with early theoretical and numerical predictions. [less ▲]

INVESTIGATION OF THE ELECTRICAL-RESISTIVITY BEHAVIOR BETWEEN THE KOSTERLITZ-THOULESS TEMPERATURE AND THE GINZBURG-LANDAU TEMPERATURE IN SPRAY-DRIED BULK BI2SR2CACU2O8+D - THE ROLE OF 2-DIMENSIONAL FLUCTUATIONS AND DEFECTS

in Physica C (1995), 251(3-4), 337-347

The resistive transition R(T) between the Kosterlitz-Thouless temperature and the Ginzburg-Landau temperature was studied in spray-dried bulk Bi2Sr2CaCu2O8+d superconductors for a magnetic-field range ... [more ▼]

The resistive transition R(T) between the Kosterlitz-Thouless temperature and the Ginzburg-Landau temperature was studied in spray-dried bulk Bi2Sr2CaCu2O8+d superconductors for a magnetic-field range between 0 and 0.3 T. The samples were prepared by the spray-drying technique with Bi2+xSr2-x-yCa2+yCu2O8+d for x = y = 0.05 or 0.1 as a starting composition here. The data analysis was performed assuming various resistive laws previously proposed. When numerically analyzed in terms of a two-dimensional Kosterlitz-Thouless theory the results lead to remarkable quantitative agreement. This implies that the R(T) behavior can be described within a picture of a highly two-dimensional behavior of macroscopic fluctuations of vortex-antivortex depairing type. The role of defects or inhomogeneities in the resistive behavior is outlined. [less ▲]

BI-BASED 2223 SUPERCONDUCTING POLYCRYSTALLINE MATERIALS PREPARED BY EITHER A SOLID-STATE ROUTE OR A GLASSY MATRIX PRECURSOR METHOD - CHEMICAL-ANALYSIS AS WELL AS ELECTRICAL AND THERMAL TRANSPORT-PROPERTIES

in Physica C (1994), 231(3-4), 259-270

Two routes have been followed in order to prepare Bi1.7Pb0.3Sr2Ca2Cu3O(y) superconducting materials. Bi1.7Pb0.3CuO4 is always used as one of the starting basic materials. The first route involves a new ... [more ▼]

Two routes have been followed in order to prepare Bi1.7Pb0.3Sr2Ca2Cu3O(y) superconducting materials. Bi1.7Pb0.3CuO4 is always used as one of the starting basic materials. The first route involves a new experimental procedure based on the solid state synthesis of separate intermediate phases, mixed together in a two (Bi1.7Pb0.3CuO4 + 2SrCaCuO3), three (Bi1.7Pb0.3CuO4+2SrCuO2+2CaCO3) or four (Bi1.7Pb0.3CuO4+(1/12)Sr8Ca6Cu24O41 + (3/2)CaCO3 + (4/3)SrCO3) powder process. Electric resistivity versus temperature measurements are presented. Even though the T(c)(0) of each sample is above 100 K, X-ray diffraction shows that the main phase is the 2212 phase in each case. Relatively pure 2223 materials have, however, successfully been produced by the second method, which starts from a glassy intermediate phase and involves a so-called 'matrix' method. The glass precursor phase is composed of one (Bi1.7Pb0.3CuO4), two (Bi1.7Pb0.3CuO4 + 2CaCO3), and three (Bi1.7Pb0.3CuO4 + (3/2)CaCO3 + (4/3)SrCO3) components as for the solid state routes. The role of both the added alkaline earth crystalline compounds and the glass matrix precursors in this second method turns out to be very important. We propose a schematic structural model in order to explain the selectivity of the starting materials. SrCaCuO3 is found to be a good precursor of the 2212 phase, while SrCuO2 gives rise to the 2223 phase. It seems that the presence of CaCO3 in the glassy intermediate phase, thus acting as a cation reservoir, is very useful for the production of the 2223 phase. Electric resistivity, thermal conductivity and thermopower versus temperature measurements are also presented and discussed in terms of intergrowths and variations of cationic compositions in the Bi-based layers. [less ▲]