Strain engineering of magnetic and orbital order in perovskite LuMnO3 epitaxial films

Epitaxial strain has been extensively used to tailor the functionality of perovskite oxides, in which strain control of magnetism is highly desirable, especially for perovskite manganites. Here on the basis of the first-principles calculations we demonstrated the control of magnetic phase and orbital order in ${\mathrm{LuMnO}}_{3}$ film by epitaxial strain imposed by a square substrate and revealed the surface and interface effects by combining the strain-bulk and heterostructure models. The spiral and $E$ -type multiferroic phases present in perovskite manganites bulks can exist in the tensile strained films, while a ferromagnetic half-metal phase with high Curie temperature and an antiferromagnetic polar-metal phase arise in the range of compressive strain. Increasing compressive strain changes the sign of the ${Q}_{3}$ mode of Jahn-Teller distortion, resulting in the transition of the in-plane stagger orbital order to a uniform orbital order. The reconstruction of Jahn-Teller distortion and orbital order occur in the first two layers near the surface. The symmetry breaking of the crystal field at the surface leads to a uniform ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ type orbital order and surface metallization. The electron accumulation at the interface with ${\mathrm{SrTiO}}_{3}$ substrate has been demonstrated and decreases dramatically with the increase in the number of ${\mathrm{LuMnO}}_{3}$ layers.