Transport studies of YBa₂Cu₃O_y/Y_xPr _1-xBa₂Cu₃O_y and YBa₂Cu₃O_y/R_0.7M _0-3MnO₃ superlattices, in which R = La or Nd, and M = Ca or Sr

We report the transport studies of YBa₂Cu₃O_y/Y_xPr _1-xBa₂Cu₃O_y and YBa₂Cu₃Oy/R_1-xM_xMnO ₃ superlattices in magnetic fields in which R = La or Nd, and M = Ca or Sr. The X-ray diffraction of samples shows superlattice structure. The resistive transition in a magnetic field shows thermal activated behavior. The flux pinning is reduced when the coupling strength between YBCO layers is decreased. The angular dependence of the critical current of YBa₂Cu₃O_y/PrBa₂Cu ₃O_y superlattices reveals the dimensionality of superlattices. The magnetoresistance ratio (MR),|Δρ(H = 7 T) - Δρ(H = 0)|/Δρ(H = 7 T), of YBa₂Cu₃O_y/R_1-xM _xMnO₃ superlattices is affected by the layer coupling of R_1-xM_xMnO₃ layers. The enhancement of the MR ratio in the tri-layer YBa₂Cu₃O_y/La_0.7M _0.3MnO₃/YBa₂Cu₃O_y film in the low temperature regime is significant and has a value of 33650% at T = 75 K. We attribute this enhancement of the MR to the ordering of magnetic moment in ferromagnetic layers in magnetic fields. The results are discussed in terms of existing theories.