Transport properties of YBa2Cu3O7-δ/La0.7Ca0.3MnO3 multilayers

• Main Authors: Ji-Cheng Chen, 陳智城
• Other Authors: 楊鴻昌
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/34723229558906831097

碩士 === 國立臺灣大學 === 物理學研究所 === 89 === (YBa2Cu3O7-δ/La0.7Ca0.3MnO3) multilayers were in situ grown onto SrTiO3 substrates by an rf magnetron sputtering system. Surface roughness and lattice structures of multilayers are examined by AFM(Atomic Force Microscope) and X-ray diffractions. Resistivity and Hall coefficients of multilayers are measured by a standard four points DC method. Superconductivity of YBa2Cu3O7-δ and negative magneto-resistance of La0.7Ca0.3MnO3 are both kept in multilayers. TC of multilayers are affected by layer thickness of La0.7Ca0.3MnO3. When magnetic fields are applied, resistive broadenings happen in mixed states and negative magneto-resistance occurs above TC. Variations of resistive curves due to applied fields in mixed states can be understood by TAFF(Thermally Activated Flux Flow) behaviors. Pinning energies derived by the Anderson-Kim model are calculated from Arrhenius plots and linear to logarithm of applied fields, which correspond to results of other multilayers. Different width of resistive broadenings when applied magnetic fields are perpendicular or parallel to samples indicates anisotropy and different pinning mechanism of multilayers. Sign reversals of Hall coefficients also occur in mixed states of (YBa2Cu3O7-δ/La0.7Ca0.3MnO3) multilayers. This strange behavior cannot be understood thoroughly by pinning of magnetic fluxes. Other influences on sign reversals should be studied by more experiments.