Confinement of magnetism in quantum oxide layers

At crystalline interfaces where a valence mismatch exists, chemical, electronic and structural interactions may occur to relieve the polar mismatch leading to the stabilization of non-bulk phases. We show that spontaneous reconstructions at polar $LaSrMnO_3$ interfaces are correlated with suppressed ferromagnetism for film thicknesses on the order of a unit cell. We demonstrate the stabilization of ferromagnetic ordering in two-dimensional doped rare earth manganite layers by alleviating the valence mismatch at polar manganite interfaces. Using a combination of synchrotron X-ray scattering and magnetic spectroscopy and temperature dependent magnetometry we find that chemically inserting atomic layers of $La_{0.7}Sr_{0.3}CrO_3$ spacers at $La_{0.7}Sr_{0.3}MnO_3$ interfaces leads to robust long range ferromagnetic ordering for $La_{0.7}Sr_{0.3}MnO_3$ thicknesses down to two unit cells. These results underscore the critical importance of interfacial structural and magnetic interactions in the fabrication of two-dimensional oxide magnetic systems.