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Abstract: Polycrystalline perovskite cobalt oxides Sr1– xRx CoO3 (R=Y and Ho; ) were prepared by high-pressure/high-temperature technique. X-ray powder patterns of the Y-system indicated cubic perovskite form for , and orthorhombic perovskite form for and 1.0, while coexisting of the two phases for . The cubic perovskite samples had metallic electric resistivities while the orthorhombic ones with semiconducting or insulating nature. The parent compound SrCoO3 showed a ferromagnetic transition at 266K. With the Y substitution, the transition temperature increased slightly to ∼275K at , then decreased rapidly to ∼60K for . The YCoO3 () sample showed non-magnetic behavior. The Ho-substituted system showed quite similar structural, transport and magnetic properties to those of the Y-system. [Copyright &y& Elsevier]

Abstract: Ho-based 1212 niobio-cuprate (Nb-1212Ho) was synthesized for the first time. An off-stoichiometric starting composition Nb0.9Sr2HoCu2.1O7.9 led a phase-pure polycrystalline sample under the synthesis condition at 1450°C for 2h at 6GPa, approximating the true bulk composition. X-ray diffraction pattern clearly indicated an Nb-1212 type structure for the compound with lattice parameters a = b =3.8505(1)Å and c =11.574(3)Å, suggesting that the space group P4/mmm is likely for the structure. Unlike Nb-1212Y, the Nb-1212Ho compound showed neither superconductivity nor a magnetic order down to 1.8K. A relatively large magneto-resistance approximately −7% was found at 30K. [Copyright &y& Elsevier]

Abstract: Polycrystalline perovskite cobalt oxides (Sr1– x Ca x )CoO3 (0⩽x⩽0.8) were synthesized under high pressure (6GPa) and high temperature (1200–1300 °C) conditions. Powder X-ray diffraction data confirmed that they have cubic perovskite structures. The end member of the solid solution, SrCoO3, exhibited a ferromagnetic transition with Curie temperature of and metallic electric conductivity. With increasing the Ca content , increased slightly to 286K at then decreased rapidly to 148K for . The origin of the ferromagnetism is discussed in relation to the spin state of the Co4+ ions. The present system showed a relatively large (∼5.5%) negative magnetoresistance for or 0.2 in the vicinity of T c. [Copyright &y& Elsevier]

Additional charge carriers were introduced to the iron oxyarsenide Sr2ScFeAsO3 under a high-pressure condition, followed by measurements of electrical resistivity, the Hall coefficient, and magnetic susceptibility. The host compound Sr2ScFeAsO3 shows metallic conductivity down to ∼200 K and turns to show a semiconducting-like conductivity accompanied by a positive magnetoresistance (22% at 70 kOe). Although the carrier density is comparable at 300 K (5.9 × 1021 cm-3) with that of the other Fe-based superconductors, no superconductivity appears down to 2 K. This is primarily because the net carrier density decreases over three orders of magnitude on cooling and additionally a possible magnetic order at ∼120 K prevents carriers from pairing. The properties were altered largely by introducing the additional carriers. [ABSTRACT FROM AUTHOR]

Abstract: 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 5d 2, 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 band. [Copyright &y& Elsevier]

Abstract: The Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method using KOs2O6 as a host. The composition was identified as Na1.4Os2O6·H2O by electron probe micro-analysis, thermogravimetric analysis, and structural analysis using synchrotron X-ray diffraction. Na1.4Os2O6·H2O crystallizes in a regular pyrochlore structure with some defects (space group: Fd-3m, a=10.16851(1)Å). Electrical resistivity, heat capacity, and magnetization measurements clearly showed absence of superconductivity down to 2K, being in large contrast to what was found for the β-type pyrochlore superconductor AOs2O6 (A=Cs, Rb, and K). The Sommerfeld coefficient is 22mJK−2 mol−1, being the smallest among AOs2O6. A magnetic anomaly at ∼57K and associated magneto-resistance (+3.7% at 2K in 70kOe) were found. [Copyright &y& Elsevier]

Abstract: Co nuclear quadrupole resonance (NQR) measurements were performed on the bilayer hydrate cobaltate compound under hydrostatic pressures to study the pressure effect on the superconducting (SC) and magnetic properties. We found that the hydrostatic pressure increases the NQR frequency and suppresses the SC transition temperature . The relationship between and observed in the present pressure-dependent measurements is different from that observed in sample-dependent NQR measurements. Nuclear spin–lattice relaxation rate was also measured under several pressures. The results indicate that the magnetic fluctuations are suppressed with applying pressures. The pressure effect on can be understood as the suppression of magnetic fluctuations, which act as the glue to form the cooper pairs. From the pressure effect on asymmetric parameter of the electric-field gradient, we suggest a possible explanation for the difference between sample dependence and pressure dependence. [Copyright &y& Elsevier]

The magnetic behavior of polycrystalline samples of the magneto-superconductors RuSr2Ln1.5Ce0.5Cu2O10-δ (LnRu-1222, Ln=Y, Ho and Dy) and RuSr2YCu2O8-δ (YRu-1212) is analyzed and compared. Clear evidences for the occurrence of a spin glass phase on all LnRu-1222 samples are provided by ac susceptibility (χac) and dc magnetization measurements. A frequency-dependent peak in χac vs. T measurements, at low magnetic field, is observed. The strong suppression of this peak in the presence of magnetic fields as low as 500 Oe, as well as the results of thermoremanent magnetization (TRM) and isothermal remanent magnetization (IRM) measurements, suggest a spin glass behavior. Interestingly, the same measurements on the YRu-1212 sample show no indication of glassy behavior, contrasting with the results for LnRu-1222. We suggest that frustration of the Ru magnetic moments due to the presence of oxygen vacancies would be favored only in the LnRu-1222 compounds, thus causing the glassy behavior. This idea is supported by the observation of large oxygen deficiency that affects the RuO2 planes in Ru-1222, but does not occur in Ru-1212. [Copyright &y& Elsevier]

Abstract: The magnetic properties of solid solution Sr4− x Ba x Mn3O10 (, 1, 2, 3 and 4) were investigated. These were well characterized as two-dimensional antiferromagnets with Mn4+ (S=). The magnetic susceptibility of every sample showed a broad maximum due to short-range ordering at around 80K. The kinks in the susceptibility and peaks in the specific heat data indicated T N. The T N increased from 67 to 78K with increasing x. [Copyright &y& Elsevier]

The dynamics of the magnetic properties of polycrystalline RuSr2Ln1.5Ce0.5Cu2O10 (LnRu-1222, Ln=Gd, Y, Ho, Nd) have been studied by ac susceptibility. A frequency-dependent cusp was observed in χac vs. T measurements, which is interpreted as a spin-glass transition. These results are contrasted with the regular antiferromagnetic transition observed for YRu-1212. [Copyright &y& Elsevier]