Optical Properties of Buffer and Superconducting Layers of the YBa_2Cu_3O_(7-delta)/La_(1.75)Ba_(0.25)CuO_4/La_(0.8)Ba_(0.2)MnO_3 Heterostructure for Second-Generation Superconducting Cables on an Ni5 percent W Tape

摘要

An epitaxial YBa_2Cu_3O_(7-delta)/La_(1.75)Ba_(0.25)CuO_4/La_(0.8)Ba_(0.2)MnO_3 heterostructure has been obtained on a biaxially textured tape of an Ni5 percent W alloy. It is shown that when films of a buffer layer of La_(0.8)Ba_(0.2)MnO_3 applied onto a tape of an Ni alloy in a reducing atmosphere are annealed in an oxygen atmosphere it is the compensation of oxygen vacancies that plays the dominant role in the formation of optical and magnetooptical properties of the layer, rather than stresses at the film-substrate interface. The shape of the reflection spectrum of the buffer layer after annealing corresponds to that of an La_(0.8)Ba_(0.2)MnO_3 single crystal, which indicates that the oxygen content is close to the stoichiometric one. The temperature dependences of the transverse Kerr effect and coefficient of light reflection of the films at a fixed wavelength can be used for the evaluation of T_c and the temperature of the optical response of the metal-insulator transition of the buffer layer on the basis of lanthanum manganite.