  Tailoring spin-orbit interactions and Coulomb repulsion are the key features
to observe exotic physical phenomena such as magnetic anisotropy and
topological spin texture at oxide interfaces. Our study proposes a novel
platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3
(3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls
the lattice displacement and spin-correlated interfacial coupling through
charge transfer. We report on a tunable and enhanced interface-induced Rashba
spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3
bilayer with change in the underlying magnetic order of LaMnO3. We also
observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to
previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals
the quantitative valence of Mn and their impact on charge transfer. Further, we
performed angle-dependent magnetoresistance measurements, which show signatures
of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of
LaMnO3. Our work thus demonstrates a new route to engineer the interface
induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide
interfaces which makes SrIrO3 an ideal candidate for spintronics applications.
