Transport studies of YBa 2Cu 3O y/Y xPr 1− xBa 2Cu 3O y and YBa 2Cu 3O y/ R0.7M0–3MnO 3 superlattices, in which R=La or Nd, and M=Ca or Sr

Abstract

We report the transport studies of YBa 2Cu 3O y /Y x Pr 1− x Ba 2Cu 3O y and YBa 2Cu 3Oy/ R 1− x M x MnO 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 YBa 2Cu 3O y /PrBa 2Cu 3O y superlattices reveals the dimensionality of superlattices. The magnetoresistance ratio (MR), |Δ ρ( H=7 T)−Δ ρ( H=0)|/Δ ρ( H=7 T), of YBa 2Cu 3O y / R 1− x M x MnO 3 superlattices is affected by the layer coupling of R 1− x M x MnO 3 layers. The enhancement of the MR ratio in the tri-layer YBa 2Cu 3O y /La 0.7 M 0.3MnO 3/YBa 2Cu 3O 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.