Selective interlayer ferromagnetic coupling between the Cu spins in YBa(2)Cu(3)O(7−x) grown on top of La(0.7)Ca(0.3)MnO(3)

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa(2)Cu(3)O(7−x) (YBCO) superconductor when it is grown on top of ferromagnetic La(0.7)Ca(0.3)MnO(3) (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO(2) but not with La(0.7)Ca(0.3)O interfacial termination. Such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO(2) plane at the La(0.7)Ca(0.3)O and MnO(2) terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.