Search

A layered iridate Ba2IrO4 was synthesized using a high-pressure synthesis technique. Its electronic state was studied through electrical resistivity, magnetic susceptibility, and μSR experiments. It was found that Ba2IrO4 crystallizes in a K2NiF4-type structure (space group I4/mmm) with lattice parameters a =4.030(1) Å and c =13.333(4) Å. The structure includes flat IrO2 square planar lattices with straight Ir-O-Ir bonds. Ba2IrO4 is a Mott insulator (activation energy ΔEa ∼ 0.07 eV) driven by a spin-orbit interaction. The magnetic susceptibility and μSR studies revealed that the magnetic ground state is antiferromagnetic long-range order (TN ∼ 240 K) in which the magnetic moment (∼0.34μB/Ir atom) is significantly reduced by a low-dimensional quantum spin fluctuation with a large intraplane correlation ∣J∣. The behavior is similar to that in parent materials of high-TC cuprate superconductors such as La2CuO4. [ABSTRACT FROM AUTHOR]

We have used the ac magnetic susceptibility to investigate the vortex state in an optimally doped p-type Ba0.5K0.5Fe2As2 single crystal under various ac and dc fields. A peak effect is observed in the temperature dependence of the in-phase ac susceptibility, indicating an order-disorder transition on the vortex phase diagram. The peak effect displays an anomalous history effect compared with other type-II superconductors, which we ascribe to the strong pinning existing in the material. We observe the development of a small dissipation peak at the temperature Tp2 slightly below the peak effect region. Similar to the peak effect boundary, Tp2 delimits a region in the H-T phase diagram which is independent on the ac field amplitude. We argue that this small peak may arise from the softening of the vortex lattice, leading to a collective pinning of the whole vortex lattice. This effect assists and further enhances the peak effect occurring in the Ba0.5K0.5Fe2As2 superconductor. [ABSTRACT FROM AUTHOR]

Resonant soft x-ray powder diffraction experiments on orthorhombic TmMnO³ and LuMnO³ are presented. Experiments were performed in the vicinity of the Tm M⁵ and the Mn L²,³ edges to study the Tm and Mn magnetic moments, respectively. These experiments show that for the heavy rare-earth perovskite with an E-type ordered ground state, the Tm magnetic moments order already in the nonferroelectric incommensurate magnetic phase. Additionally, deviations from the collinear E-type Mn magnetic structure at low temperatures are found for both compounds. These experiments show the power of resonant soft x-ray diffraction, extended to polycrystalline 4f materials. [ABSTRACT FROM AUTHOR]

75As and 139La NMR and nuclear quadrupole resonance (NQR) studies on Zn-substituted LaFeAsO0.85 have been performed to microscopically investigate the Zn-impurity effects. Although superconductivity in LaFeAsO0.85 disappears by 3% Zn substitution, we found that NMR/NQR spectra and NMR physical quantities in the normal state are hardly changed, indicating that the crystal structure and electronic states are not modified by Zn substitution. Our results suggest that the suppression of superconductivity by Zn substitution is not due to the change of the normal-state properties, but due to strong nonmagnetic pair-breaking effect to superconductivity. [ABSTRACT FROM AUTHOR]

A dense phase of a postlayered perovskite Sr3Co2O6 was created by a high-pressure and high-temperature synthetic route and quenched to ambient conditions. The structure of Sr3Co2O6 was determined by synchrotron x-ray powder diffraction. Sr3Co2O6 crystallizes in a K4CdCl6-type structure (an infinite chain-type structure), which is 6% denser than the known isocompositional layered perovskite Sr3Co2O7-δ (δ ∼ 1). The K4CdCl6-type Sr3Co2O6 shows complex magnetic behavior, reflecting its spin-chain nature, as do the analog oxides Ca3Co2O6 and Ca3CoRhO6, whose microscopic magnetic origin is still highly debated. [ABSTRACT FROM AUTHOR]

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]