Tracking BO$_{\mathrm{6}}$ Coupling in Perovskite Superlattices to Engineer Magnetic Interface Behavior*

In the past several years, control of BO$_{\mathrm{6}}$ octahedral coupling at ABO$_{\mathrm{3\thinspace }}$perovskite interfaces has emerged as a new tool for engineering of interface properties due to its strong coupling to polar and magnetic properties. High resolution data on tilt transitions at interfaces is instrumental for evaluating the validity of existing theoretical models and developing predictive theories. Recently, we have developed a unique method to investigate BO$_{\mathrm{6}}$ rotation patterns in complex oxides with unit cell resolution. Our method involves column shape analysis in ABF-STEM images of the perovskite heterointerfaces taken in specific orientations. This method will allow us to determine local symmetry between adjacent unit cells, revealing the BO$_{\mathrm{6}}$ coupling behavior at heterointerfaces in 3D. This technique was used to characterize structure and predict properties via a combined STEM and DFT study of magnetic superlattice of La(Ca)MnO$_{\mathrm{3}}$/La(Sr)MnO$_{\mathrm{3}}$ with different periodicities, which exhibit a range of electromagnetic coupling behaviors. We will also discuss the prospects for tilted structure determination using electron ptychography. The correlations among the BO$_{\mathrm{6}}$ rotation, domain size, superlattice periodicity and the electromagnetic coupling will be discussed in detail.