Enhanced flux pinning in a high- T C superconducting film by a ferromagnetic buffer layer

A YBa 2 Cu 3 O 7 (30 nm) superconductor layer and a YBa 2 Cu 3 O 7 (30 nm)/ Pr 0.67 Sr 0.33 MnO 3 (30 nm) superconducting/ferromagnetic bilayer were epitaxially grown on the single-crystal (100) SrTiO 3 substrates. Magnetic characterizations on both samples were very carefully performed over wide temperature and field ranges. The enhanced flux pinning by the ferromagnetic layer in the bilayer sample is clearly seen in the comparison of the temperature-dependent magnetization data obtained in the zero-field-cooled and field-cooled processes for both samples. The fact that the temperature-dependent remanent magnetization in the bilayer shows a sharper transition near the T C than that in the YBCO single layer is also consistent with the picture of the enhanced flux pinning. The above observations are confirmed by the enhanced critical current density, J c ∝ Δ M , where Δ M is the magnetic irreversibility in the hysteresis loops.