title: Crystal structural, magnetic, and transport properties of layered cobalt oxyfluorides, Sr2CoO(3+x)F(1-x) (0 ≤ x ≤ 0.15).
abstract: The crystal structure of the layered cobalt oxyfluoride Sr(2)CoO(3)F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr(2)CoO(3)F is an antiferromagnetic insulator with the Néel temperature T(N) = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ(B) at 3 K, consistent with the high spin electron configuration for the Co(3+) ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt.
authors.affiliation: International Center for Young Scientists (ICYS) and International Center for Materials Nanoarchitechtonics (WPI-MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan. Tsujimoto.Yoshihiro@nims.go.jp
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Tsujimoto
authors.forename: Clastin I
authors.initials: CI
authors.lastname: Sathish
authors.forename: Kun-Pyo
authors.initials: KP
authors.lastname: Hong
authors.forename: Kengo
authors.initials: K
authors.lastname: Oka
authors.forename: Masaki
authors.initials: M
authors.lastname: Azuma
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Guo
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Matsushita
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yamaura
authors.forename: Eiji
authors.initials: E
authors.lastname: Takayama-Muromachi