Spin and orbital magnetic moments of rhenium in AAЈFeReO 6 double perovskites ͑A , AЈ = Ba, Sr, and Ca͒ have been directly probed employing x-ray magnetic circular dichroism at the Re L 2,3 edges. A considerable orbital magnetic moment is observed in all the compounds studied, which confirm theoretical predictions of unquenched Re orbital moment despite its octahedral coordination. Relative orbital-to-spin moment ratio alters with lattice distortion from m L / m S = −0.285 to − 0.337 from Ba 2 FeReO 6 to Ca 2 FeReO 6 , respectively. Moreover, the spin moment of Re ion scales with Curie temperature, the most relevant property in spin electronics application of the compounds studied. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2234292͔ Ordered double perovskites have recently attracted great interest due to their large spin polarization and Curie temperature ͑T C ͒ much higher than room temperature. These properties are strongly desired in order to realize reasonable magnetoresistance effects at room temperature, which is not only a challenging subject of fundamental science but also an important phenomenon for potential applications in spin electronics. Therefore the first observation of substantial magnetoresistance at room temperature in Sr 2 FeMoO 6 ͑Ref. 1͒ quickly led to production of magnetic tunnel junctions and magnetoresistive potentiometers.Currently, the other ordered double perovskites AAЈBBЈO 6 ͑A , AЈ = Ca, Sr, Ba, La, etc.; BBЈ = FeMo, FeRe, CrRe, CrW, etc.͒ are being intensively studied in order to find a material with optimal performance. 2-7 Among them the Re-based double perovskites are the most promising compounds in terms of high Curie temperature, e.g., 538 and 635 K in Ca 2 FeReO 6 and Sr 2 CrReO 6 , respectively.3 Moreover, Re-based double perovskites are magnetically hard 4,6,8 and reveal large magnetoelastic effects, 9 which can only be explained by a substantial magnetocrystalline anisotropy due to the anisotropy of an unquenched orbital moment of Re.

A systematic study of the valence states of Mn and Co in the perovskite series LaMn 1−x Co x O 3 ͑x = 0 to 1͒ by means of x-ray absorption near edge spectroscopy ͑XANES͒ at the K-edges is presented. The chemical shift and the evolution of the pre-edge features reveal a gradual increase of the average oxidation level of both, Mn and Co ions, with Co doping, which suggests that mixed valence states of Co 2+ /Co 3+ and Mn 3+ /Mn 4+ exist in the whole solid solution range. The relation of the results to the magnetic properties of the compounds is discussed.

The structure of glassy Te(78)Ge(11)Ga(11), Te(79)Ge(16)Ga(5), Te(70)Ge(20)Se(10) and Te(73)Ge(20)I(7)--promising materials for far infrared applications--was investigated by means of x-ray and neutron diffraction as well as extended x-ray absorption fine structure measurements at various edges. Experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo simulation technique. Short range order in Te(85)Ge(15) was reinvestigated by fitting a new x-ray diffraction measurement together with available neutron diffraction and extended x-ray absorption fine structure data. It was found that Te(85)Ge(15) consists mostly of GeTe(4) structural units linked together directly or via bridging Te atoms. Te is predominantly twofold coordinated in Te(85)Ge(15), Te(70)Ge(20)Se(10) and Te(73)Ge(20)I(7) while in Te(78)Ge(11)Ga(11) and Te(79)Ge(16)Ga(5) the Te coordination number is significantly higher than 2. The Te-Te bond length is 2.80 ± 0.02 Å in Te(78)Ge(11)Ga(11) while it is as short as 2.70 ± 0.02 Å and 2.73 ± 0.02 Å in Te(73)Ge(20)I(7) and Te(70)Ge(20)Se(10), respectively. Our results show that the strengths of GeTe(4) (GeTe(3)I, GeTe(3)Se) 'units' are very similar in all glasses investigated but the connection between these units depends on the third component. Differences in the Te coordination number suggest that unlike Se or I, Ga does not build into the Ge-Te covalent network. Instead, it forms a covalent bond with the non-bonding p electrons of Te, which results in an increase in the average Te coordination number.

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