title: Spin-orbital superstructure in strained ferrimagnetic perovskite cobalt oxide.
abstract: We have investigated the Co-3d spin-orbital state in a thin film of perovskite LaCoO3 to clarify the origin of strain induced spontaneous magnetization (T(C)=94 K) by means of x-ray diffraction, optical spectroscopy, and magnetization measurements. A lattice distortion with the propagation vector (1/4 -1/4 1/4) and an anomalous activation of optical phonons coupled to Co-3d orbital are observed below 126 K. Combined with the azimuthal angle analysis of superlattice reflection, we propose that the ordering of Co-3d orbital promoted by an epitaxial strain produces a unique ferrimagnetic structure.
authors.affiliation: Department of Applied Physics and Quantum-Phase Electronics Center, University of Tokyo, Hongo, Tokyo 113-8656, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Fujioka
authors.forename: Y
authors.initials: Y
authors.lastname: Yamasaki
authors.forename: H
authors.initials: H
authors.lastname: Nakao
authors.forename: R
authors.initials: R
authors.lastname: Kumai
authors.forename: Y
authors.initials: Y
authors.lastname: Murakami
authors.forename: M
authors.initials: M
authors.lastname: Nakamura
authors.forename: M
authors.initials: M
authors.lastname: Kawasaki
authors.forename: Y
authors.initials: Y
authors.lastname: Tokura