Two-dimensional ~La$_{2/3}$Sr$_{4/3}$MnO$_{4}$ Manganite Films Probed by Epitaxial Strain and Cation Ordering

Dimensionality is known to play a central role in the properties of strongly correlated systems. Here we investigate magnetism and transport in thin films of the Ruddlesden-Popper n=1 phase, La$_{1-x}$Sr$_{1+x}$MnO$_{4}$. Within this material, the~MnO$_{6}$-octahedra~form two-dimensional perovskite sheets~separated by an extra rocksalt layer. By fabricating high quality thin films with ozone-assisted molecular beam epitaxy, we study how the effects of epitaxial strain and intentional cation ordering, known as digital synthesis, influence the properties of this 2-dimensional manganite. For example, at the same Mn$^{3+}$:Mn$^{4+}$ ratio (2:1) as its fully spin-polarized 3D manganite counterpart, this two dimensional analog at x=1/3 only displays a spin glass phase below 20K in bulk.~This is believed to result from a competition between superexchange and double exchange, as well as disordered Jahn-Teller distortions.~ However, in our films we find weak ferromagnetic order up to much higher temperatures in addition to a low temperature spin glass phase. We will discuss how strain and cation order effect the presence of this weak ferromagnetism.