Diffusion-controlled complex superconducting transition in (YBa2Cu3O7-δ)0.9/(La2/3Sr1/3MnO3)0.1 core-shell composites

The superconductor (SC)/ferromagnetic (FM) systems have shown tremendous attention due to their amazing phenomena at the SC/FM interfaces such as the inverse proximity effect, triplet superconducting pair generation and the non-dissipation spintronics, which exhibit a great potential on scientific development and applications. To explore these unique characteristics, possible unknown effect and seeking for potential capabilities in bulk SC/FM systems, this study focuses on the bulk composites made of the high-T_C superconductor YBa₂Cu₃O_7-δ (YBCO) and the highly spin-polarized La_2/3Sr_1/3MnO₃ (LSMO). The (YBCO)_0.9/(LSMO)_0.1 composites were annealed at short (Comp₂hr) and longer (Comp₁8hr) annealing time. We found that the composites form a distinct core-shell structure. The LSMO grains and the outer layer of YBCO interdiffuse into each other and reconstruct in a way to form off-stoichiometric thin shells. Due to the limited interdiffusion speed, a clear white diffusion-limited-boundary separates the shell and core and protects the pure YBCO phase. This core-shell structure modifies the superconducting behavior to appear complex resistivity and magnetization with temperature such as a second transition due to the tunneling of Cooper pairs at low temperature.