Effect of nonstoichiometry on properties of La{sub 1-t}MnO{sub 3+{delta}}. III. Magnetic order studied by power neutron diffraction
- Institutt for energiteknikk, Kjeller (Norway)
- Univ. of Oslo (Norway)
The magnetic order, moments, and ordering temperatures for La{sub 1-t}MnO{sub 3+{delta}} depend strongly on its nonstoichiometry. Powder neutron diffraction samples were obtained via precursor based synthesis, annealing in atmospheres with controlled oxygen partial pressures, and adequate quenching or slow cooling. The samples are representative for most of the nonstoichiometric domain. Three modifications of La{sub 1-t}MnO{sub 3+{delta}} were studied. First, the reduced phase with Jahn-Teller deformed Mn{sup III} is orthorhombic (ORT1) and orders antiferromagnetically (A{sub x} mode), typically T{sub N} {approximately} 140 K and {mu}{sub AF} {approximately} 3.4 {mu}{sub B} (0.00 {le} t {le} 0.08). All samples of this type exhibit parasitic ferromagnetism. Second, the fully oxidized samples have average Mn oxidation state around 3.2, and have rhombohedral (RH) crystal structure with ferromagnetic order at low temperatures; T{sub c} {approximately} 213 {plus_minus} 10 K and {mu}{sub F} = 3.9 {plus_minus} {mu}{sub B} for La{sub 0.96}MnO{sub 3.05}. Third, for intermediate oxygen contents an orthorhombic structure (ORT2) occurs, with minor distortions of the MnO{sub 6}-octahedra. For LaMnO{sub 3.08} of ORT2-type, ferromagnetic order (F{sub y} mode) occurs below T{sub C} = 125 {plus_minus} 10 K. The ordered magnetic moment, {mu}{sub F} = 2.46 {plus_minus} 0.04 {mu}{sub B} is rather small. LaMnO{sub 3.15} also takes the ORT2-type structure at low temperature, as proved by weak super-structure reflections. At 200 {plus_minus} 20 K, LaMnO{sub 3.15} undergoes a first order transition to the RH-type. The ordered magnetic moment, if present, is very small and in any case far from expectations for Mn{sup III}/Mn{sup IV} mixtures. It is proposed that the approximately 3:1 ratio between Mn{sup III} and Mn{sup IV} atoms in LaMnO{sub 3.15} gives rise to a frustrated system with largely spin glass behaviour.
- OSTI ID:
- 390899
- Journal Information:
- Journal of Solid State Chemistry, Vol. 124, Issue 1; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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