Novel orbital ordering induced by anisotropic stress in a manganite thin film

A novel structure of orbital ordering is found in a Nd0.5Sr0.5MnO3 thin film, which exhibits a clear first-order transition, by synchrotron x-ray diffraction measurements. Lattice parameters vary drastically at the metal-insulator transition at 170Â K (=TMI), and superlattice reflections appear below 140Â K (=TCO). The electronic structure between TMI and TCO is identified as A-type antiferromagnetic with a dx2-y2 ferro-orbital ordering. The new type of antiferro-orbital ordering characterized by the wave vector (141412) in cubic notation emerges below TCO. The accommodation of the large lattice distortion at the first-order phase transition and the appearance of the novel orbital ordering are brought about by the anisotropy in the substrate, a new parameter for the phase control.