The perovskite La1/3Sr2/3FeO3−δ was investigated by neutron diffraction, magnetic and Mössbauer spectroscopy measurements. La1/3Sr2/3FeO3−δ undergoes magnetic ordering at T = 190–200 K accompanied by charge disproportionation. Magnetic peaks due to charge ordering are observed below 200 K. The charge ordering is gradually developed below 200 K along with a charge disproportionation, 2Fe4+ ⇒ Fe3+ + Fe5+. La1/3Sr2/3FeO3−δ shows an antiferromagnetic structure at low temperature. Magnetic moments of about 3 and 1.3 μB were obtained from the neutron diffraction data refinement for Fe3+ and Fe5+ at 15 K, respectively, which suggest that both Fe ions are in a low spin state. These values are significantly lower than those reported by Battle et al for La1/3Sr2/3FeO2.98. Mössbauer spectra indicate that full charge ordering might be reached below 20 K with no Fe4+.

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Magnetic interactions in perovskite compounds of the type La 1Ϫx Sr x MO 3Ϫ␦ ͑M ϭ3d transition such as Mn and Fe͒ are presumed to arise through a super exchange between 3d electrons of the magnetic ions via oxygen orbitals. The magnetic structure of La 0.6 Sr 0.4 FeO 3Ϫ␦ has been studied with neutron diffraction. Oxygen vacancies were created by annealing samples under various gases including N 2 , air and mixtures of CO/CO 2 . All La 0.6 Sr 0.4 FeO 3Ϫ␦ compounds maintain the rhombohedral structure ͑space group R3 c͒. The air-or oxygen-annealed samples have almost no oxygen vacancies while those made in the reducing atmosphere show 7%-11% oxygen vacancies. The rhombohedral distortion decreases in the reduced samples. All the samples exhibit antiferromagnetic ordering at room temperature, although a small ferromagnetic moment may also be present. The samples with little or no oxygen vacancies show a room temperature magnetic moment of ϳ1.4 B at the Fe site while those having Ͼ7% oxygen vacancies show a moment of ϳ4.0 B . Magnetization measurements reveal a much higher magnetic ordering temperature in samples with oxygen vacancies

A recent study of (SmGd)Fe14Si3 showed an anomalous x-ray diffraction pattern [P. C. Ezekwenna, G. K. Marasinghe, J.-H. Nam, W. J. James, W. B. Yelon, M. Ellouze, and Ph. I’Héritier, J. Appl. Phys. 87, 6716 (2000)]. Although all observed peaks could be indexed to the rhombohedral 2:17 phase (R-3m) many lines were strongly reduced in intensity. Subsequently, the same phenomenon was seen in neutron diffraction patterns from Nd2−xDyxFe17−ySiy alloys and conventional refinement using the rhombohedral phase left significant residuals. Fourier mapping revealed additional density along the c-axis chains of Fe dumbbells and rare earth atoms. The perfect a-b-c stacking of the CaCu5 layers with regular 1/3 replacement of the rare earth atoms by Fe dumbbells appears to be broken. Detailed analysis shows that excess Fe dumbbells are incorporated into the structure and some reverse substitution is seen. In addition, the weak intensities are associated with a near equivalence of the 9d and 18h Fe sites, as in the parent CaCu5 phase. The relationship of this new structure to the other CaCu5 derived phases is described. The high Fe concentration creates the possibility of high TC and higher remanence than in the ordered 2:17 compounds.

The heavy fermion compound UPdIn is found to absorb deuterium without disproportionation to yield UPdInD 0.7 . Magnetization, heat capacity, x-ray, and neutron-diffraction measurements have been carried out to probe the structural and magnetic properties of this deuteride. It is found that deuterium absorption results in a highly anisotropic lattice expansion, without changing the Fe 2 P-type hexagonal structure of the parent compound. The magnetic ordering temperature is enhanced to 80 K and the low-temperature uranium moment to 2.5 B from their corresponding values of 21 K and 1.5 B , respectively, in the parent compound. Neutrondiffraction studies on the deuteride reveal antiferromagnetic ordering of the uranium moments and doubling of unit cell along the c axis. Heat capacity measurements show a large reduction in the value of electronic specific heat coefficient ␥ from 260 mJ mol Ϫ1 K Ϫ2 in UPdIn to 30 mJ mol Ϫ1 K Ϫ2 in UPdInD 0.7 , indicating a significant reduction in the hybridization between uranium 5 f electrons and those on the surrounding atoms.