The nanoscale control of disorder-to-order layer-stacking boosts multiferroic responses in an Aurivillius-type layered oxide

The manipulation of layer-stacked interfaces inside layered perovskite oxide structures can lead to collective phenomena and extraordinary functionalities, originating from local structural distortions near correlated interfaces and the broken inversion symmetry of periodically repeating layer cells. In this work, the nanoscale control of disorder-to-order layer stacking was achieved in an Aurivillius-type layered oxide, with the structure of a basic perovskite motif sandwiched between Bi-O layers, through simple stoichiometric ratio control or ion substitution at A- and/or B-sites. Tunable layer structure evolution from a disordered mixed-layer structure composed of 4-layer and 5-layer phases to a homogeneous layer structure was clearly observedviautilizing X-ray diffraction and Raman techniques. Such layer structure modulation induces variable mixed-layer interfaces and special OPB defects, which generate perturbations in local order parameters, such as polarization and strain, thus giving rise to enhanced ferroelectric and magnetic properties, anomalous magnetic behavior, and magnetodielectric effects. More importantly, the use of minor La and Co co-doping in phase-modulated materials can generate much larger magnetic coercive fields, reaching ∼20 kOe at 50-100 K, arising from strong interactions between the anti-ferromagnetic matrix and short-range ferromagnetic clusters. Our findings offer a route to the rational fabrication of functional layered perovskites and shed new light on the design of single-phase multiferroics, with the potential for feature-rich applications.