Confinement of magnetism in atomically-thin $La_{0.7}Sr_{0.3}CrO_3$/$La_{0.7}Sr_{0.3}MnO_3$ heterostructures

At crystalline interfaces where a valence mismatch exists, electronic and structural interactions may occur to relieve the polar mismatch leading to the stabilization of non-bulklike phases. We show that spontaneous reconstructions at polar $La_{0.7}Sr_{0.3}MnO_3$ interfaces are correlated with suppressed ferromagnetism for film thicknesses on the order of a unit cell. We investigate the structural and magnetic properties of valence-matched $La_{0.7}Sr_{0.3}CrO_3$ - $La_{0.7}Sr_{0.3}MnO_3$ interfaces using a combination of high-resolution electron microscopy, first principles theory, synchrotron X-ray scattering and magnetic spectroscopy and temperature-dependent magnetometry. A combination of an antiferromagnetic coupling between the $La_{0.7}Sr_{0.3}CrO_3$ and $La_{0.7}Sr_{0.3}MnO_3$ layers and a suppression of interfacial polar distortions are found to result in robust long range ferromagnetic ordering for ultra-thin $La_{0.7}Sr_{0.3}MnO_3$. These results underscore the critical importance of interfacial structural and magnetic interactions in the design of devices based on two-dimensional oxide magnetic systems.