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Crystals of the compound [Ca.sub.3]LiOs[O.sub.6] are grown by a flux method by using LiCl and KCl, which is followed by single-crystal X-ray diffraction (XRD), low-temperature XRD, and measurements of ac and dc magnetic susceptibility and specific heat. The original superexchange magnetic path Os-O-Os is absent and hence the extended superexchange path (Os-O)-(O-Os) is responsible for the 117 K magnetic order.

In continuation of the series of perovskite oxides that includes 3d4 cubic BaFeO3 and 4d4 cubic BaRuO3, 5d4 cubic BaOsO3 was synthesized by a solid-state reaction at a pressure of 17 GPa, and its crystal structure was investigated by synchrotron powder X-ray diffraction measurements. In addition, its magnetic susceptibility, electrical resistivity, and specific heat were measured over temperatures ranging from 2 to 400 K. The results establish a series of d4 cubic perovskite oxides, which can help in the mapping of the itinerant ferromagnetism that is free from any complication from local lattice distortions for transitions from the 3d orbital to the 5d orbital. Such a perovskite series has never been synthesized at any d configuration to date. Although cubic BaOsO3 did not exhibit long-range ferromagnetic order unlike cubic BaFeO3 and BaRuO3, enhanced feature of paramagnetism was detected with weak temperature dependence. Orthorhombic CaOsO3 and SrOsO3 show similar magnetic behaviors. CaOsO3 is not as conducting as SrOsO3 and BaOsO3, presumably due to impact of tilting of octahedra on the width of the t2g band. These results elucidate the evolution of the magnetism of perovskite oxides not only in the 5d system but also in group 8 of the periodic table. [ABSTRACT FROM AUTHOR]

Carbon-for-nitrogen substitution (51 at% at most) was achieved in the antiferromagnetic metallic host material Mn3ZnN. The various carbon-doped compounds were studied using synchrotron X-ray diffraction, and their electrical resistivities, specific heats, and degrees of magnetization were measured for temperatures of 2--400 K. The sharp antiferromagnetic-to-paramagnetic transition of the host material at 185 K broadened markedly as the carbon content was increased, and a significant ferromagnetic character was found to coexist with the antiferromagnetism when the carbon concentration exceeded 27 at%. This critical magnetic behavior is likely in part due to the increase in the density of states at the Fermi level and the increase in the distance between neighboring Mn atoms. The exact mechanism responsible for the induction of die complicated magnetic state could not be determined. However, the results demonstrate dearly that the chemical tuning of the X site in antiperovskite Mn3AX materials is as useful as that of the A and Mn be used to develop the properties of these materials for practical applications. [ABSTRACT FROM AUTHOR]

The postspinel mineral MgAl2O4 exists only under the severe pressure conditions in the subducted oceanic lithosphere in the Earth's deep interior. Here we report that its analogous oxide CdRh204 exhibits a structural transition to a quenchable postspinel phase under a high pressure of 6 GPa at 1400 °C, which is within the general pressure range of a conventional single-stage multianvil system. In addition, the complex magnetic contributions to the lattice and metal nonstoichiometry that often complicate investigations of other analogues of MgAl2O4 are absent in CdRh204. X-ray crystallography revealed that this postspinel phase has an orthorhombic CaFe204 structure, thus making it a practical analogue for investigations into the geophysical role of postspinel MgAl2O4 Replacement of Mg2+ with Cd2+ appears to be effective in lowering the pressure required for transition, as was suggested for CdGeO3. In addition, Rh3+ could also contribute to this reduction, as many analogous Rh oxides of aluminous and silicic minerals have been quenched from lower-pressure conditions. [ABSTRACT FROM AUTHOR]

Crystals of the newly synthesized compound Ca3LiOsO6 were grown by a flux method using LiCl and KCl, followed by single-crystal X-ray diffraction (XRD), low-temperature powder XRD, and measurements of ac and dc magnetic susceptibility and specific heat. The data indicate that Ca3LiOsO6 has a fully opened electronic gap with an antiferromagnetic ordered state, consistent with suggestions from the first-principles study. The observed magnetic transition temperature is 117 K, too high to be caused only by a direct spin-spin interaction. It appears that the original superexchange magnetic path Os-O-Os is absent; thus, the extended superexchange path (Os-O)-(O-Os) can be expected to be responsible for the 117 K magnetic order. If this is true, Ca3LiOsO6 would be highly valuable to study the nature of extended superexchange magnetic interactions in solids. [ABSTRACT FROM AUTHOR]

5d and 3d hybrid solid-state oxide Ca2FeOsO6 crystallizes into an ordered double-perovskite structure with a space group of P21/n with high-pressures and temperatures. Ca2FeOsO6 presents a long-range ferrimagnetic transition at a temperature of 320 K (Tc) and is not a band insulator, but is electrically insulating like the recently discovered Sr2CrOsO6 (Tc 725 K). The electronic stat of Ca2FeOsO6 is adjacent to a half-metallic state as well as that of Sr2CrOsO6. In addition, the high-Tc ferrimagnetism was driven by lattice distortion, which was observed for the first time among double-perovskite oxides and represents complex interplays between spins and orbitals. Unlike conventional ferrite and garnet, the interplays likely play a pivotal role of the ferrimagnetism. A new class of 5d-3d hybrid ferrimagnetic insulators with high-Tc is established to develop practically and scientifically useful spintronic materials. [ABSTRACT FROM AUTHOR]