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Abstract. A series of polycrystalline double perovskites SrLaBIrO6 (B = Ni, Mg, Zn) containing Ir5+ (5d4) was synthesized by solid state reactions and structural, magnetic and electronic properties were investigated. The isotypic fully ordered double perovskites crystallize in space group P21/n and show semiconducting behavior with estimated bandgaps of approximately 0.2 eV for SrLaNiIrO6 and SrLaZnIrO6, and 0.4 eV for SrLaMgIrO6. SrLaNiIrO6 is an antiferromagnet with a Néel temperature of 74 K (μeff = 3.3 μB, θW = -90 K), whereas SrLaMgIrO6 and SrLaZnIrO6 are weakly paramagnetic. All title compounds exhibit a temperature-independent contribution to the measured magnetic susceptibility, which supports the notion for a van-Vlecktype response originating from the Ir5+ (5d4, Jeff = 0) ions. [ABSTRACT FROM AUTHOR]

A layered Sr2Co0.5Ir0.5O4 (space group I4/ mmm) perovskite of the K2NiF4 structure type was synthesized as a single-phase sample. Neutron powder diffraction measurements revealed full site occupancy of oxygen atoms. The Co3+/Ir5+ valence states were evaluated by a combination of X-ray absorption and X-ray photoemission spectroscopy as well as by magnetization measurements, and thus the differences to the parent compounds Sr2CoO4 and Sr2IrO4 with similar structures were confirmed. Co- K edge EXAFS studies indicated a long average Co-O distance of 1.967 Å suggesting a high-spin state of the Co3+ ion in Sr2Co0.5Ir0.5O4. No long-range magnetic ordering down to 4 K was detected by neutron powder diffraction, probably hindered by the random distribution of Co and Ir cations in the Sr2Co0.5Ir0.5O4 structure. High-pressure synchrotron powder diffraction studies showed stability of the Sr2Co0.5Ir0.5O4 structure up to at least 27 GPa at room temperature. A maximum in the c/a ratio at 10 GPa together with an anomaly in the pressure dependence of the unit-cell volume could be a sign of a change in the spin state of the Co ions under pressure. [ABSTRACT FROM AUTHOR]

Low-temperature (200 °C) hydrothermal synthesis of the ruthenium oxides Ca1.5Ru2O7, SrRu2O6, and Ba2Ru3O9(OH) is reported. Ca1.5Ru2O7 is a defective pyrochlore containing RuV/VI; SrRu2O6 is a layered RuV oxide with a PbSb2O6 structure, whilst Ba2Ru3O9(OH) has a previously unreported structure type with orthorhombic symmetry solved from synchrotron X-ray and neutron powder diffraction. SrRu2O6 exhibits unusually high-temperature magnetic order, with antiferromagnetism persisting to at least 500 K, and refinement using room temperature neutron powder diffraction data provides the magnetic structure. All three ruthenates are metastable and readily collapse to mixtures of other oxides upon heating in air at temperatures around 300-500 °C, suggesting they would be difficult, if not impossible, to isolate under conventional high-temperature solid-state synthesis conditions. [ABSTRACT FROM AUTHOR]

• Antiphase-free and full inverted nanopillar thin films of cobalt ferrite inverse-spinel was obtained. • The largest x-ray magnetic circular dichroism signal of divalent cobalt at room temperature was observed. • X-ray absorption spectra and x-ray magnetic circular dichroism spectra were nicely reproduced by full atomic multiplet theory. • The enhanced performance of the cobalt ferrite inverse-spinel nanopillar thin film plausibly comes from its appropriate size. The ongoing quest for defect-free thin films systems that are apt for being used as spin filtering materials for spintronic applications did yet not deliver satisfying results regarding materials that would be up to the pertinent requirements. Using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Co-L 2,3 and Fe-L 2,3 absorption edges, we have investigated the magnetic properties of a nanostructured thin film with self-assembled CoFe 2 O 4 nanopillars embedded in BiFeO 3 , the latter being a well-known system for its combined multiferroic and spintronic properties. In this BiFeO 3 -CoFe 2 O 4 heterostructure we observed a significant XMCD signal at the Co-L 2,3 edges which turns out to be the largest among the presently reported for Co ions at room temperature. A quantitative analysis of the Co-L 2,3 spectra unveils that such a large Co-L 2,3 XMCD signal stems from the impeccable fully inverted spinel ordering of the A- and B-sites in antiphase-free CoFe 2 O 4 nanopillars. This twofold perfect CoFe 2 O 4 ordering feature yields an unprecedented optimization within a multifunctional ferrimagnetic-multiferroic thin film system highly relevant for spintronic applications, also resulting in an equally unprecedented macroscopic magnetic moment for such material as compared to its pure form as well as to technologically relevant thin film compound systems. [ABSTRACT FROM AUTHOR]

A layered Sr2Co0.5Ir0.5O4 (space group I4/ mmm) perovskite of the K2NiF4 structure type was synthesized as a single-phase sample. Neutron powder diffraction measurements revealed full site occupancy of oxygen atoms. The Co3+/Ir5+ valence states were evaluated by a combination of X-ray absorption and X-ray photoemission spectroscopy as well as by magnetization measurements, and thus the differences to the parent compounds Sr2CoO4 and Sr2IrO4 with similar structures were confirmed. Co- K edge EXAFS studies indicated a long average Co-O distance of 1.967 Å suggesting a high-spin state of the Co3+ ion in Sr2Co0.5Ir0.5O4. No long-range magnetic ordering down to 4 K was detected by neutron powder diffraction, probably hindered by the random distribution of Co and Ir cations in the Sr2Co0.5Ir0.5O4 structure. High-pressure synchrotron powder diffraction studies showed stability of the Sr2Co0.5Ir0.5O4 structure up to at least 27 GPa at room temperature. A maximum in the c/a ratio at 10 GPa together with an anomaly in the pressure dependence of the unit-cell volume could be a sign of a change in the spin state of the Co ions under pressure. [ABSTRACT FROM AUTHOR]

Ca1.5Ru2O7 (I), SrRu2O6 (II), and Ba2Ru3O9(OH) (III) are hydrothermally synthesized from aqueous mixtures of KRuO4 and MO2 (M: Ca, Sr, Ba; autoclave, 200 °C, 24 h). [ABSTRACT FROM AUTHOR]