Synthesis and characterization of nanosized ferrites from the thermolysis of strontium and barium tris(succinato)ferrate(III) precursors J. Appl. Phys. 109, 07B510 (2011); 10.1063/1.3537949On magnetic properties and domain structure of strontium ferrite particles A series of strontium ferrate compositions ranging from SrFe02.7 to SrFeOa.n have been produced by equilibration at oxygen pressures ranging from 0.2 to 855 atm. The stoichiometric composition SrFeOa.n exhibits a simple cubic perovskite structure (a=3.850 A). Ceramic disks of this material are conductive (p""lQ-a {l.cm) and their temperature dependence is characteristic of metallic conduction. Magnetic measurements indicate that SrFeOs.o is antiferromagnetic below 130 o K. With increasing oxygen deficiency, specimens show increased cell constants and eventually tetragonal distortion. Decrease in the Neel temperature and increased resistivity accompany these changes. 4 H. Wantanabe, J.
Mössbauer spectra were measured at 4°, 78°, and 300°K for the two end members and two intermediate samples of the system SrFeO2.5–3.0. Of primary interest is the spectrum of strontium ferrate (IV) which at 300°K consists of a single unsplit line having a full width at half-intensity of 0.39 mm/sec and an isomer shift relative to copper of —0.171 mm/sec. At 4° and 78°K the spectra consist of six lines with an ISCu of —0.079 mm/sec and an hfs of 331 and 290 kOe, respectively. There is no evidence of quadrupole splitting, consistent with the cubic perovskite structure. The spectra of the pure iron (III) compound are composed of two sets of six-line spectra having ISCu of +0.126 and —0.047 mm/sec and hfs of 489 and 407 kOe, respectively, at 300°K. By analogy with YIG, it was concluded that the structure should contain equivalent amounts of octahedrally and tetrahedrally coordinated iron sites. Subsequent structural analysis confirmed this conclusion and indicated that the phase is isomorphic with brownmillerite. The spectra of the intermediate compounds were found to be more complex and are discussed in terms of accompanying changes in stoichiometry and structure.
Two series of manganate phases have been prepared and their magnetic properties measured. The first series consists, in addition to CaMn0 3 , of three phases having layered structures. In these, tetravalent magnanese ions are contained in single or multiple perovskite layers which are separated from each other by nonmagnetic calcium-oxygen layers. Magnetic exchange of the type Mn 4+ -0-Mn 4+ is disrupted between layers, and decreased Neel temperatures were expected to result. In a second series of phases, the size of of the CaMnOs unit cell was increased by partial substitution of strontium for calcium. Increased separation of manganese ions produced by this means was expected to reduce Neel temperatures. However, contrary to these expectations, Neel temperatures remained approximately constant for the first series of phases and increased for the second.
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