Diamagnetic and resistive properties of undoped and Na-doped (Ca 1−χSr χ) 1− yNa yCuO 2 ( y=0−0.2) infinite-layer thin films grown by laser molecular beam epitaxy

Abstract

Thin films of Ca 1−χSr χCuO 2 ( x=0.2−1.0) and (Ca 1−χSr χ) 1− y Na y CuO 2 ( x=0−1.0, y=0.2) have been grown by successive deposition of (Ca, Sr, Na) and CuO 2 layers in No 2 ambient. X-ray diffraction analyses have confirmed the formation of the infinite-layer structure of (Ca 1−χSr χ) 1− y Na y CuO 2 with c-axis orientation. For the undoped films, lattice constant c and electrical conductivity increase systematically with increasing Sr/Ca ratio. Clear diamagnetic signals at 90 and 125 K have been observed for the SrCuO 2 and Cu 0.4Sr 0.6CuO 2 thin films, respectively. In contrast to the undoped Ca 1−χSr χCuO 2 films with the sam e Sr/Ca ratio, lattice constant c of the Na-doped films varies linearly and electrical conductivity increases due to the Na substitution. Similarly to the undoped films, the Na-doped (Ca 1−χSr χ) 0.8Na 0.2CuO 2 films show diamagnetic signals at 90 and 130 K. Resistive anomalies at corresponding temperatures are shown to depend on the measuring current and applied magnetic field.