Evidence of charge transfer in a bilayer film, LaSrMnO3/YBa2Cu3O7

We study the growth and electronic properties of a high temperature superconductor, YBa$_2$Cu$_3$O$_7$ (YBCO) in proximity of a magnetic material, La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO). High quality single crystalline films of YBCO and LSMO/YBCO were grown epitaxially on SrTiO$_3$ (001) surface. Magnetization data of the LSMO/YBCO bilayer exhibit ferromagnetic ordering with Curie temperature smaller than that of pure LSMO. Measurements at different field directions reveal emergence of an anisotropy at low temperatures with in-plane easy axis; the observed anisotropy is stronger in the superconducting region. Magnetization data of YBCO exhibit onset of diamagnetism at 86 K for the out-of-plane magnetic measurements while the in-plane measurements show onset at a slightly higher temperature of 89 K with much smaller moment. Interestingly, the onset of diamagnetism in LSMO/YBCO film remains at 86 K despite the presence of ferromagnetic LSMO layer underneath. The analysis of Ba 4$d$ and Y 3$d$ core level spectra suggest that the surface and bulk electronic structure in these systems are different; the difference is reduced significantly in the LSMO/YBCO sample suggesting an enhancement of electron density near the surface arising from the charge transfer across the interface, which is consistent with the magnetization data.