Orbital Ordering Structures in (Nd, Pr)_<0.5>Sr_<0.5>MnO_3 Manganite Thin Films on Perovskite (011) Substrates(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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Structural study of orbital-ordered manganite thin films has been conducted using synchrotron radiation, and a ground state electronic phase diagram is made. The lattice parameters of four manganite thin films, Nd_<0.5>Sr_<0.5>MnO_3 (NSMO) or Pr_<0.5>Sr_<0.5>MnO_3 (PSMO) on (011) surfaces of SrTiO_3 (STO) or [(LaAlO_3)_<0.3>(SrAl_<0.5>Ta_<0.5>O_3)_<0.7>] (LSAT), were measured as a function of temperature. The result shows, as expected based on previous knowledge of bulk materials, that the films' resistivity is closely related to their structures. Observed superlattice reflections indicate that NSMO thin films have an antiferro-orbital-ordered phase as their low-temperature phase while PSMO film on LSAT has a ferro-orbital-ordered phase, and that on STO has no orbital-ordered phase. A metallic ground state was observed only in films having a narrow region of A-site ion radius, while larger ions favor ferro-orbital-ordered structure and smaller ions stabilize antiferro-orbital-ordered structure. The key to the orbital-ordering transition in (011) film is found to be the in-plane displacement along [011] direction.
社団法人日本物理学会の論文
2008-01-15