  Flexible magnetic materials with robust and controllable perpendicular
magnetic anisotropy (PMA) are highly desirable for developing flexible
high-performance spintronic devices. However, it is still challenge to
fabricate PMA films through current techniques of direct deposition on
polymers. Here, we report a facile method for synthesizing single-crystal
freestanding SrRuO3 (SRO) membranes with controlled crystal structure and
orientation using water-soluble Ca3-xSrxAl2O6 sacrificial layers. Through
cooperative effect of crystal structure and orientation engineering, flexible
SrRuO3 membranes reveal highly tunable magnetic anisotropy from in-plane to
our-of-plane with a remarkable PMA energy of 7.34*106 erg/cm3. Based on the
first-principles calculations, it reveals that the underlying mechanism of PMA
modulation is intimately correlated with structure-controlled Ru 4d-orbital
occupation, as well as the spin-orbital matrix element differences, dependent
on the crystal orientation. In addition, there are no obvious changes of the
magnetism after 10,000 bending cycles, indicating an excellent magnetism
reliability in the prepared films. This work provides a feasible approach to
prepare the flexible oxide films with strong and controllable PMA.
