Neutron-diffraction study of structural transition and magnetic order in orthorhombic and rhombohedral La7/8Sr1/8Mn1-γO3+δ
Abstract
We report on a systematic neutron powder diffraction (NPD) study of polycrystalline La7/8Sr1/8Mn1-γO3+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 R\bar
{3}c (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) μB/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) μB/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 eg-band.- Publication:
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Journal of Physics Condensed Matter
- Pub Date:
- April 2007
- DOI:
- 10.1088/0953-8984/19/17/176226
- Bibcode:
- 2007JPCM...19q6226L