Structure, magnetism, and spin-phonon coupling in heteroepitaxial La2CoMnO6/Al2O3(0001) films

Double perovskite $\mathrm{L}{\mathrm{a}}_{2}\mathrm{CoMn}{\mathrm{O}}_{6}$ (LCMO) thin films with the monoclinic $P{2}_{1}/n$ structure were grown on hexagonal $c$-cut sapphire substrates by metalorganic aerosol deposition technique. Epitaxial growth of $\mathrm{LCMO}(021)/\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}(0001)$ due to an almost perfect in-plane lattice matching between LCMO and $\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ was evidenced by x-ray diffraction and transmission electron microscopy. A high degree of rock-salt-type Co/Mn ordering was directly visualized by means of high resolution transmission electron microscopy. The $B$-site ordering, influenced by the film growth rate and optimized by small compressive epitaxial strain, results in perfect magnetic properties and strong spin-phonon coupling, both necessary requisites for multiferroic performance.