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.

•Polycrystalline bulk compound LaZnAsO was synthesized for the first time.•Oxygen deficiency was introduced up to 35 at.% under a high pressure of 6 GPa.•The semiconductivity was highly robust against the oxygen deficiency up to 25 at.%.LaZnAsO has been studied mainly in the thin film form that was indicated as a wide-gap insulator with the gap size of ∼2.3 eV. We herein report the synthesis of polycrystalline bulk LaZnAsO compound for the first time under a high pressure of 6 GPa. Effect of oxygen deficiency on the electric and magnetic properties of the compound was also investigated by synchrotron X-ray diffraction and measurements of electrical resistivity, magnetic susceptibility, isothermal magnetization, and specific heat. The bulk LaZnAsO crystallized into the ZrCuSiAs-type structure with the space group P4/nmm, isostructural with the layered LaFeAsO. It is semiconducting with a thermal activation energy of ∼0.8 eV, and the semiconductivity was highly robust against oxygen deficiency up to 25 at.%. The virtue will benefit the development of a diluted magnetic semiconductor.Graphical abstract

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.

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 the complicated magnetic state could not be determined. However, the results demonstrate clearly that the chemical tuning of the X site in antiperovskite Mn3AX materials is as useful as that of the A and Mn sites and can be used to develop the properties of these materials for practical applications.

Na doping of post-spinel CdRh2O4 was achieved over the full composition range to NaRh2O4 using high-pressure and high-temperature synthesis conditions. X-ray diffraction analysis confirmed that Na occupies the Cd site and that the host structure is retained, in sharp contrast to what was observed for spinel CdRh2O4, where Na was not accommodated at all. As the Na content was increased, the electrically insulating state changed to a conducting state at a critical composition close to x = 0.75 in Cd1−xNaxRh2O4. The specific heat data confirm that the density of electronic states at the Fermi level was enhanced around this composition, suggesting that the metal–insulator transition is likely induced by band filling. In addition, unusual antiferromagnetism was observed in several compounds with intermediate Na concentrations, and this phenomenon was seemingly independent of the metal–insulator transition.Graphical abstractHighlights► Full-range substitution of Na for Cd was achieved in post-spinel CdRh2O4. ► The host structure was retained for all Na concentrations. ► In contrast Spinel CdRh2O4 does not accommodate Na under similar conditions. ► The Na substitution caused a metal–insulator transition.

Single-crystal Ca10(Pt4As8)(Fe1.8Pt0.2As2)5 superconducting (SC) nanowhiskers with widths down to hundreds of nanometers were successfully grown in a Ta capsule in an evacuated quartz tube by a flux method. Magnetic and electrical properties measurements demonstrate that the whiskers have excellent crystallinity with critical temperature of up to 33 K, upper critical field of 52.8 T, and critical current density of Jc of 6.0 × 105 A/cm2 (at 26 K). Since cuprate high-Tc SC whiskers are fragile ceramics, the present intermetallic SC whiskers with high Tc have better opportunities for device applications. Moreover, although the growth mechanism is not understood well, the technique can be potentially useful for growth of other whiskers containing toxic elements.

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 CdRh2O4 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 CdRh2O4. X-ray crystallography revealed that this postspinel phase has an orthorhombic CaFe2O4 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.

The antiperovskite Mn3ZnN is studied by neutron diffraction at temperatures between 50 and 295 K. Mn3ZnN crystallizes to form a cubic structure at room temperature (C1 phase). Upon cooling, another cubic structure (C2 phase) appears at around 177 K. Interestingly, the C2 phase disappears below 140 K. The maximum mass concentration of the C2 phase is approximately 85% (at 160 K). The coexistence of C1 and C2 phase in the temperature interval of 140–177 K implies that phase separation occurs. Although the C1 and C2 phases share their composition and lattice symmetry, the C2 phase has a slightly larger lattice parameter (Δa ≈ 0.53%) and a different magnetic structure. The C2 phase is further investigated by neutron diffraction under high-pressure conditions (up to 270 MPa). The results show that the unusual appearance and disappearance of the C2 phase is accompanied by magnetic ordering. Mn3ZnN is thus a valuable subject for study of the magneto-lattice effect and phase separation behavior because this is rarely observed in nonoxide materials.

The superconducting and lattice properties of δ-MoC0.681 were studied by electromagnetic measurements, synchrotron X-ray diffraction, neutron diffraction, and electron diffraction. The superconducting properties (Tc=12 K) of δ-MoC0.681 were well characterized by a weak coupling model. The carbon vacancies present in the host cubic structure were found to be robust, although the material was synthesized from stoichiometric carbon and Mo powder under a high-pressure of 6 GPa. A thermodynamically-stable structure with ordered vacancies did not account for the robust features of δ-MoC0.681 since the vacancies are unlikely to be ordered in long range in the host structure. A model based on inherent phonon instability theoretically predicted for a stoichiometric MoC phase might be responsible for the robust features of δ-MoC0.681.Graphical AbstractThe cubic molybdenum carbide shows an excellent superconductivity with robust carbon vacancies. Inherent phonon instability theoretically predicted for a stoichiometric MoC phase might be responsible for the vacancies rather than a thermodynamically-stable structure with vacancies ordering Highlights► The 12 K superconductivity is well characterized by a weakly coupling model. ► Carbon vacancies are robust and disordered in the cubic host structure. ► Inherent phonon instability might be responsible for the robust carbon vacancies in δ-MoC0.681.

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.

Na2OsO4 crystals were grown by a NaCl flux method under high pressure. It crystallizes in the Ca2IrO4-type structure without having additional elements or metal vacancies, which are usually accommodated. It appears that Na2OsO4 is a metal-stoichiometric Ca2IrO4-type compound never been synthesized to date. Na2OsO4 has the octahedral environment of Os6+O6 so that the electronic configuration is 5d2, suggesting the magnetic S=1 ground state. However, magnetization, electrical resistivity, and specific heat measurements indicated that the non-magnetic S=0 state is much likely for Na2OsO4 than the S=1 state. Band structure calculations and the structure analysis found that the disagreement is probably due to the statically uniaxial compression of the OsO6 octahedra, resulting in splitting of the t2gt2g band.Na2OsO4 crystals were grown by a NaCl flux method under high pressure. It crystallizes in the Ca2IrO4-type structure comprising infinite Os6+O6 octahedra (5d2) chains. The crystal growth, the crystal structure, and the magnetic and electrical properties are reported.

•Flux jumps were observed inpoly-crystalline Ba0.5K0.5Fe1.9M0.1As2 (M = Fe, Co, Ni, and Zn).•Much high density of flux jumps were observed for the Zn-doped Ba0.5K0.5Fe1.9Zn0.1As2.•Single crystals of Ba0.5K0.5Fe2As2 and Ba0.5K0.5Fe1.9Zn0.1As2 are absent of flux jumps.Polycrystals of Ba0.5K0.5Fe1.9M0.1As2 (M = Fe, Co, Ni, Cu, and Zn) synthesized at high pressures show quasi-periodic spikes in the magnetization loop at 2 K owing to successive flux jumps, while the single crystals are observed as absence of jumps. The Zn-doped crystal indicates higher frequency flux jumps than that of Zn-free samples, because of the reduction of grain size and enhancement of grain boundary effect. However, the Co-, Ni- and Cu-doped crystals show less jumps duo to the increased granularity. Our present results suggest that the flux jump in the textured polycrystals is controlled largely by the grain boundary as the flux pining effect rather than the intrinsic dopants.