Emergence of bulk-like ferromagnetism in ultrathin freestanding manganite membranes via sacrifice-layer engineering

The development of freestanding complex oxide membranes, particularly of strongly correlated manganites, opens new avenues for heterointegration and quantum material design. However, a fundamental challenge remains in understanding the strain evolution upon release from the substrate, given the critical role of electron–lattice coupling. Here, we fabricate (001)-oriented freestanding La_0.67Sr_0.33MnO₃ (FS-LSMO) membranes using water-soluble sacrificial layers with distinct lattice constants, Sr₃Al₂O₆ (SAO) and SrCa₂Al₂O₆ (SCAO). We find that SCAO-released LSMO membranes, subjected to smaller initial interfacial stress, retain a significantly larger saturation magnetization and higher Curie temperature (T _C) than SAO-released counterparts. This correlation indicates that the long-range interfacial stress is converted into a short-range internal stress, which may be mediated by morphological adaptation and defect pinning. Most notably, these optimized membranes exhibit a drastically weak thickness dependence, sustaining robust room-temperature ferromagnetism in layers as thin as 8 u.c., overcoming the pervasive “dead-layer” effect. Furthermore, we constructed stacked FS-Pb(Zr_0.52Ti_0.48)O₃ (FS-PZT) on FS-LSMO multiferroic heterostructures, which exhibits excellent ferroelectric properties. Our work establishes a pathway to achieving high-performance, ultrathin manganite membranes for advanced spintronic and quantum architectures.