title: Neutron-diffraction study of structural transition and magnetic order in orthorhombic and rhombohedral La(7/8)Sr(1/8)Mn(1-γ)O(3+δ).
abstract: We report on a systematic neutron powder diffraction (NPD) study of polycrystalline La(7/8)Sr(1/8)Mn(1-γ)O(3+δ) compounds. We investigated the structural and magnetic phases and transitions in the temperature range between 10 and 900 K for two different samples: an Ar-annealed sample with an orthorhombic Pbnm (Z = 4; O) structure at room temperature and an air-sintered sample with a rhombohedral [Formula: see text] (Z = 2;R) structure at room temperature. At higher temperatures, above 400 K, both samples exhibit a rhombohedral structure. For the Ar-annealed sample, a Jahn-Teller (JT) transition occurs in the orthorhombic phase at about 298 K with very large variations in the Mn-O2' and Mn-O2 bond lengths and Mn-O1-Mn bond angle on cooling from 298 to 180 K. For this sample the ferromagnetic moment at 10 K in the magnetic space group Pb'n'm amounts to 3.22(5) μ(B)/Mn. In contrast, the air-sintered sample undergoes on cooling a structural transition from rhombohedral (R) to orthorhombic (O) with a mixed phase of nearly equal R and O repartition at 120 K. Ferromagnetic order develops in this sample at about 240 K with a low-temperature moment of 3.35(4) μ(B)/Mn at 10 K. The coherent JT distortion in its orthorhombic phase occurs below some 170 K. In addition, we have determined the coherent JT distortion parameter Δ, the tolerance factor t and the one-electron bandwidth W of the e(g)-band.
authors.affiliation: Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
authors.forename: H F
authors.initials: HF
authors.lastname: Li
authors.forename: Y
authors.initials: Y
authors.lastname: Su
authors.forename: J
authors.initials: J
authors.lastname: Persson
authors.forename: P
authors.initials: P
authors.lastname: Meuffels
authors.forename: J M
authors.initials: JM
authors.lastname: Walter
authors.forename: R
authors.initials: R
authors.lastname: Skowronek
authors.forename: Th
authors.initials: T
authors.lastname: Brückel