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The preparation and manipulation of crystalline yet bendable functional complex oxide membranes has been a long-standing issue for a myriad of applications, in particular, for flexible electronics. Here, we investigate the viability to prepare magnetic and crystalline CoFe2O4 (CFO) membranes by means of the Sr3Al2O6 (SAO) sacrificial layer approach using chemical deposition techniques. Meticulous chemical and structural study of the SAO surface and SAO/CFO interface properties have allowed us to identify the formation of an amorphous SAO capping layer and carbonates upon air exposure, which dictate the crystalline quality of the subsequent CFO film growth. Vacuum annealing at 800 °C of SAO films promotes the elimination of the surface carbonates and the reconstruction of the SAO surface crystallinity. Ex-situ atomic layer deposition of CFO films at 250 °C on air-exposed SAO offers the opportunity to avoid high-temperature growth while achieving polycrystalline CFO films that can be successfully transferred to a polymer support preserving the magnetic properties under bending. Float on and transfer provides an alternative route to prepare freestanding and wrinkle-free CFO membrane films. The advances and challenges presented in this work are expected to help increase the capabilities to grow different oxide compositions and heterostructures of freestanding films and their range of functional properties., This work was funded by MICIN/AEI/10.13039/501100011033/FEDER through the projects Severo Ochoa FUNFUTURE CEX2019-00917-S and PID2020-114224RB-I00. We also acknowledge the financial support from the 2020 Leonardo Grant for Researchers and Cultural Creators BBVA Foundation, the i-link A20346-CSIC project, the National Key RD Program of China (2018YFA0305800), and the Beijing Outstanding Young Scientist Program (BJJWZYJH01201914430039). The project that gave rise to these results received the support of a fellowship from the “la Caixa” Foundation LCF/BQ/DI19/11730026. D.Z. acknowledges the funding and financial support of the Fund of Chemical Industries (Kekulé fellowship) for his Ph.D. research. The authors are thankful to R. Solanas for his help with the RHEED measurements. This work has been done in the framework of the doctorate in material science of the Autonomous University of Barcelona., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).