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Bi2-xPbxSr2Ca1-yGdyCu2O8+δ (x=0.34 and y=0.18, 0.34) crystals were grown by the self-flux method. The crystals have a cleavage thickness of only half unit cell up to two unit cells with Tc only dropping 20 K as y is increased from 0.18 to 0.34 for as-grown crystals. However, Tc increased to almost the same value of about 80 K after annealing in air regardless of the Gd doping levels. The co-doping produced enhanced flux pinning compared to the sole Gd doping. A secondary peak effect presented in crystals with x=0.34 and y=0.34 was explained by phase segregations containing Gd-rich clusters. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Various MSr[SUB2]Ycu[SUB2]O[SUBz] (M-1212 with M = Fe, Co, Al, and Ga) compounds have been synthesized through a solid-state reaction route. All these compounds are derived from the basic CuBa[SUB2]Ycu[SUB2]O[SUB7-δ] structure. Rietveld structural refinement of the room-temperature neutron diffraction data for Fe-1212 reveals that nearly half of Fe remains at the M site, while the other half goes to the Cu site in the CuO[SUB2] plane. For the M = Co, Al, and Ga compounds, the basic unit cell gets doubled due to two distinct M sites in the M-O layer and the space group Ima2, without any cation intermixing is found to be more appropriate. For the M = Fe sample, magnetic ordering of Fe spins is seen from magnetization data below 70 K. In the case of the M = Co compound, a shallow down-turn in magnetic susceptibility is seen below 150 K, indicating low-dimensional magnetic characteristics of the Co-O layer. The compounds with M = Al and Ga show paramagnetic behavior in their magnetization data down to 5 K. The oxygen content, established for each compound based on oxygen occupancies, refined from the neutron diffraction data comes close to 7.0 for each. [ABSTRACT FROM AUTHOR]

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]

We report the series of ruthenate-cuprates RuSr2LnCu2O8 (Ru-1212Ln; Ln=Y, Dy, Ho, Er), which were prepared at 1200–1300 °C under 6 GPa. High-purity sample could be obtained for every system with the ‘Ru-poor’ starting composition, Ru0.9Sr2LnCu2O7.8. It was confirmed that a solid solution of (Ru1−xCux)Sr2YCu2Oy exists and its range terminates at x∼0.1 without formation of the stoichiometric phase of RuSr2YCu2Oy. Many Y-based samples were prepared varying the Ru/Cu ratio and the oxygen contents. According to DC susceptibility measurements, ferromagnetism and superconductivity looked to coexist below approximately 40 K in some samples. However, DC resistivity was always quite high even when a sample showed a large diamagnetism in a low temperature region. These results may suggest phase separation regarding the Ru/Cu ratio in the solid solution of (Ru1−xCux)Sr2YCu2Oy, casting doubt for the coexistence of superconductivity and ferromagnetism. [Copyright &y& Elsevier]

New phases Sr8ARe3Cu4O24 (A=Sr,Ca) were discovered under high-pressure/high-temperature condition. X-ray powder diffraction and electron diffraction studies for these phases indicated that they have an ordered perovskite-type structure with cubic lattices of ∼8 A˚. They showed ferromagnetism at room temperature when they were synthesized under high-oxygen-pressure condition. The Ca-containing phase has a very high Tc of 440 K with a spontaneous magnetization of ∼1 μB/f.u. [Copyright &y& Elsevier]

Studied 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10−δ (Ru-1222) compound crystallized in a tetragonal I4/mmm space group crystal structure. Thermo-gravimetric (TG) analysis was successfully applied to establish the oxygen content of the sample studied at 9.63 per formula unit. The DC magnetization data (M vs. T) revealed magnetic transition at ∼100 K followed by superconducting transition at ∼40 K. Low field (−100⩽H⩽100 Oe) M vs. H hysteresis loop showed a lower critical field (Hc1) value of around 25 Oe. Ferromagnetic component is evidenced at 5, 10, 20 and 40 K. Near saturation field of above 5 T is observed at 5 K. Zero-field returning moment (Mr) and zero-moment coercive field (Hc) values at 5 K are 0.35μB and 250 Oe. The resistance vs. temperature (R vs. T) behaviour of the sample confirmed superconductivity at around 43 K. Superconductivity transition (Tc) is broadened under magnetic field with strong granularity like steps. [Copyright &y& Elsevier]

The samples of composition RuSr2(Ln3/4Ce1/4)2Cu2O10 with Ln=Ho, Y and Dy, being synthesized by high-pressure high-temperature (6 GPa, 1200 °C) solid-state synthesis route do crystallize in space group I4/mmm. These samples exhibit magnetic transitions at ∼150 K with significant branching of zero-field-cooled (zfc) and field-cooled (fc) magnetization and a sharp cusp in zfc at ∼100 K, followed by a possible superconducting transition at lower temperatures. All the compounds show typical ferromagnetic hysteresis loops in magnetic moment (M) vs. field (H) magnetization at 5 K. Near saturation of the moments at 5 K is achieved in above 5 T (Tesla) applied fields with a value of ∼0.80μB. At low temperatures (5 K) these compounds exhibit both superconductivity and ferromagnetism. To our knowledge these are first successfully synthesized Ru-1222 compounds with various lanthanides including Y, Dy, and Ho. The results are compared with widely reported Gd/Ru-1222 compound. [Copyright &y& Elsevier]

The authors present their studies on the band structures and on the magnetic and magnetotransport properties of the high pressure phase of Sr2-xRExCoO4 [rare earth (RE)=Gd and Y, x=0.1–0.5] compounds which were synthesized by a high pressure and high temperature technique. The authors found that as x increases, the magnetoresistance {(ρH-ρ0)/ρ0} increases up to -17% at 5 K and 7 T, which is 2.5 times higher than that for undoped Sr2CoO4, although the ferromagnetic transition drops from 255 to 200 K for the Gd doping with x=0.3. The saturation moments at low temperature are significantly enhanced for the Gd doped Sr2CoO4. Observation of a close correlation between resistance and field revealed a strong spin-dependent tunneling magnetoresistance. First-principles band structure calculations indicate that high spin polarization is present for both undoped and doped compounds. [ABSTRACT FROM AUTHOR]

Abstract: The calcium rhodate CaRhO3, which crystallizes in a perovskite structure, was synthesized for the first time. Critical conditions as such high-temperature and high-pressure were found essential to the synthesis. Electrical resistivity measurement and SQUID magnetometry on the polycrystalline sample revealed it is electrically conducting as well as SrRhO3 and there is neither magnetic transition nor superconductivity above 1.8K. This compound would offer an opportunity for research into nature of the 4d strongly correlated electrons system. [Copyright &y& Elsevier]

We report the synthesis and magnetic properties of polycrystalline Sr2Cu(Re0.69-xWxCa0.31)O6 samples with x=0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6, which were prepared by high-pressure high-temperature synthesis technique. These phases had ordered cubic perovskite structures. The pristine compound (x=0) underwent a ferromagnetic (ferrimagnetic) transition with TC∼460 K. The ferromagnetism was suppressed by the W substitution and disappears almost completely for x=0.6. Mechanism of the suppression of the magnetism is discussed assuming a localized electron system. [ABSTRACT FROM AUTHOR]

We have successfully synthesized a 1212-type niobio-cuprate with an ideal formula of NbSr2YCu2O8 by high-pressure and high temperature method. The phase-pure sample was obtained by Nb-poor Cu-rich starting composition, Nb0.9Sr2YCu2.1O7.9, at 6 GPa and 1450 °C for 2 h. The 1212-type niobio-cuprate has tetragonal lattices of a=3.853(1) Å and c=11.547(1) Å (space group P4/mmm), isostructural to Ru–1212Y phase. From magnetic measurements, it was found that superconductivity and weak ferromagnetism coexisted below ∼17 K in the Nb0.9Sr2YCu2.1O7.9 sample, although the superconducting volume fraction is still very small. [ABSTRACT FROM AUTHOR]

Roddlesden-Popper homologous series Srn+1ConO3n+1 (n =1,2,3,4, and ∞)compounds were successfully synthesized by a high pressure and high temperature technique. Structure refinement revealed that these compounds crystallize in tetragonal structures, while the compound n=∞ is cubic. These compounds are ferromagnetic with the Curie temperature decreasing from 255 K for n=1 to about 200 K for n=2-4 and down to 175 K for SrCoO3. Co4+ ions present as intermediate spin states for n=1-4, but in the low spin state in SrCoO3. Negative magnetoresistance was observed for Sr2CoO4 and found to be larger than that for SrCoO3. [ABSTRACT FROM AUTHOR]

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]

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]

We have successfully synthesized a new 1222-type Y-based niobio-cuprate for the first time with the chemical composition, NbSr2(Y1.5Ce0.5)Cu2O10 by a high-pressure and high-temperature (HPHT) technique under different synthesis conditions. Good quality (nearly single-phase) Nb1222Y polycrystalline sample was synthesized at 1,450 ○C and 6 GPa for 2 h. It crystallizes in a tetragonal symmetry of space group I4/ mmm with lattice parameters a= b=3.863(2) Å and c=28.687(5) Å, which is isostructural with the corresponding Ru1222Y (RuSr2(Y1.5Ce0.5)Cu2O10) phase. The dc-magnetic susceptibility measurements show a mixed magnetic state at ∼29 K, which is apparently associated with magneto-superconductivity. The magnetic moment ( M) versus field ( H) curve of Nb1222Y sample measured at 1.8 K looks like a hybrid and it normally ensembles for both superconducting and a ferromagnetic curve. As the field increases, a low field diamagnetic signal emerges. However, temperature dependence of electrical resistivity of Nb1222Y did not show superconductivity, but semiconducting nature with a relatively large magnetoresistance (∼6% at almost entire region). No specific heat anomaly was observed at the vicinity of the transition temperature. [ABSTRACT FROM AUTHOR]

Abstract: We recently discovered two poly-type structural phases of the new cobalt-oxide system, (CaOH)1.14CoO2 and (Ca0.85OH)1.16CoO2. The former phase is an orthorhombic form, while the latter phase is monoclinic one. Both the phases have layered structure that consists of CdI2-type CoO2 triangle-lattice layers and rock-salt-type CaOH double-atomic-plane slabs, alternately stacked along the c-axis. The two subcells have incommensurate periodicity along the a-axis, resulting in a modulated crystal structure. Each structure of the two phases is composed by different stacking manner of the CoO2 blocks. The monoclinic phase accommodates hole-carriers generated by lattice defects of the Ca ions. [Copyright &y& Elsevier]

Substitution of both Co and Mo at Ru-site in RuSr2Eu1.5Ce0.5Cu2O10-δ system takes place iso-structurally in tetragonal structure (space group I4/mmm) with full solubility. The resistance versus temperature (R versus T) behavior of the pristine sample confirmed superconductivity $(T^{R=0}_c)$ around 25 K. The DC magnetization data (M versus T) for the same sample revealed magnetic transition (Tmag) at 140 K followed by superconducting transition $(T^{\rm dia}_c)$ at 32 K. With progressive Co substitution at Ru-site both $T^{R=0}_c$ and $(T^{\rm dia}_c)$ decrease monotonically and superconductivity is not observed for x ≥ 0.10 (10 at%). The magnetic behavior of materials with Co up to x = 0.2 preserves the magnetic structure of the parent RuSr2Eu1.5Ce0.5Cu2O10-δ compound. For 0.8 ≥ x ≥ 0.2 a clear antiferromagnetic transition at TN=31 K is observed regardless of Co content. In the case of Mo-doped ruthenocuprates Ru1-xMoxSr2Eu1.5Ce0.5Cu2O10-δ, it has been found that the magnetic transition temperature decreases with x. The samples of x = 0.8 and 1.0 are found to have no magnetic or superconducting effects. The values of the superconducting transition temperature obtained from the resistivity versus temperature data increase by 4.5 and 7.0 K for x = 0.2 and 0.4 respectively, and then decrease by 17 K for x = 0.6. The observed variation of Tc with x in case of Mo has been explained in terms of a theory which combines the effects of weakening magnetic behavior and reducing carrier concentration in a phenomenological manner. [ABSTRACT FROM AUTHOR]

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]

High resolution X-ray powder diffraction studies have shown SrRhO3 to transform from an orthorhombic Pnma structure at room temperature through an intermediate Imma phase to a tetragonal I4/mcm structure near 800 °C. The orthorhombic Imma phase exists over a very limited temperature range, of less than 20°. The diffraction data suggests the Pnma to Imma transition is continuous and demonstrates that the Imma–I4/mcm transition is first order. [Copyright &y& Elsevier]

Crystal structures of a homologous series of Co-based layered cuprates, CoSr2(Y,Ce)sCu2O5+2s (s=1–3), have been investigated by high-resolution electron microscopy (HREM) and electron diffraction (ED) techniques. For all the three phases ED patterns showed double periodicity along a direction parallel to the CoO layers, indicating a regular alternation of two types of CoO4-tetrahedra chains within the layers. Also seen was ordering of the chains along the layer-stacking direction for the s=1 phase (Co-1212); ED patterns simulated based on the proposed superstructure model well reproduced the observed patterns. For the s=2 (Co-1222) and s=3 (Co-1232) phases in which an additional fluorite-type layer-block is inserted between two CuO2 planes, HREM and ED analysis revealed complete disorder of the CoO4 chains along the layer-stacking direction. This implies that the interlayer ordering is mainly controlled by the distance between the neighboring CoO layers. [Copyright &y& Elsevier]

Critical current densities (Jc) and irreversibility fields (Birr) of high-Tc superconductors AuBa2Can−1CunO2n+3 [Au-12(n−1)n, n=3,4] prepared under high pressure were determined from the hysteresis in DC magnetization loop. Both the Jc and Birr values of the Au-1234 phase were larger than those of Hg- and Bi-based cupurate superconductors, but smaller than those of the Y-123 superconductor. This result suggests that the electronic structure of Au-1234 is less anisotropic compared with the Hg- and Bi-phases. The Au-1223 phase showed very small Jc values corresponding to its small superconducting volume fraction. [Copyright &y& Elsevier]

The novel spin-chain cobalt oxide Sr5Pb3CoO12 [P6×2m, a=10.1093(2) A˚ and c=3.562 51(9) A˚ at 295 K] is reported. A polycrystalline sample of the compound was studied by neutron diffraction (at 6 and 295 K) and magnetic susceptibility measurements (5 to 390 K). The cobalt oxide was found to be analogous to the copper oxide Sr5Pb3CuO12, which is comprised of magnetic-linear chains at an interchain distance of 10 A˚. Although the cobalt oxide chains (μeff of 3.64 μB per Co) are substantially antiferromagnetic (θW=−38.8 K), neither low-dimensional magnetism nor long-range ordering has been found; a local-structure disorder in the chains might have an impact on the magnetism. This compound is highly electrically insulating. [ABSTRACT FROM AUTHOR]

Abstract: Local structure of the layered superconductor η-Mo3C2 (T c =8.5K) was studied by a neutron diffraction method. The structure comprises a triangular-lattice layer and a block layer, and the layers share a common structure basis of octahedral CMo6. We found that the block layer contains non-trivial disorders likely caused by inhomogeneous carbon distribution, while the triangular-lattice layer consists of almost perfect regular octahedra. Thus, the triangular-lattice is probably responsible for the superconductivity. [Copyright &y& Elsevier]

Abstract: The RuSr2RECu2O8 (RuRE-1212) and RuSr2RE1.5Ce0.5Cu2O10 (RuRE-1222; RE=rare earth) are the members of a class of material which exhibit both superconductivity and magnetic ordering. In this work high-pressure syntheses of the RE=Tb family and their magnetic properties are reported. They are tetragonal, RuTb-1212 belonging to P4/mmm space group, RuTb-1222 to I4/mmm. Compared to other ruthenocuprates, they show high magnetic ordering temperatures. This suggests that high magnetic moment of Tb influences the ordering of Ru moments in these compounds. [Copyright &y& Elsevier]

Abstract: The solid solution between the ferromagnetic metal and the enhanced paramagnetic metal was recently reported (Phys. Rev. B 69 (2004) 024410), and an unexpected feature was found in the specific heat data at of . The feature was reinvestigated further by characterizing additional samples with various Ru concentrations in the vicinity of . Specific heat and magnetic susceptibility data indicate that the feature reflects a peculiar magnetism of the doped perovskite, which appears only in the very narrow composition range . [Copyright &y& Elsevier]

Magnetic entropy and adiabatic temperature changes in and above the room-temperature region have been measured for La0.7Sr0.3Mn1-xMx′O3 (M′=Al,Ti) by means of magnetization and heat capacity measurements in magnetic fields up to 6 T. The magnetocaloric effect becomes largest at the ferromagnetic ordering temperature Tc that is tuned (from 364.5 K for x=0) to ∼300 K by the substitution of Al or Ti for Mn. While the substitution of Al for Mn drastically reduces the maximum magnetic entropy (-ΔSm) and adiabatic temperature (ΔTa) changes, it extends considerably the working temperature span and therefore improves the relative cooling power (RCP). Under a magnetic field change ΔH=2 T, -ΔSm (or ΔTa) of La0.7Sr0.3Mn1-xAlxO3 decreases from 2.66 J/kg K (or 1.65 K) for x=0 to 1.18 J/kg K (or 0.69 K) for x=0.1, while RCP increases from 80.3 to 108.8 J/kg, respectively. While Tc is largely suppressed, the magnetocaloric effect is only lightly affected by the Ti substitution. With ΔH=2 T, the La0.7Sr0.3Mn0.95Ti0.05O3 sample exhibits -ΔSm (or ΔTa) =2.44 J/kg K (or 1.38 K) with RCP=89.9 J/kg. The decrease of magnetic moment is found to be one possible reason behind the suppression of the MCE. The magnetocaloric effect in manganite materials seems to be inhibited by the existence of short-range ferromagnetic correlations above Tc. [ABSTRACT FROM AUTHOR]

We investigate the magnetotransport properties of La0.7Ca0.3-xAgxMnO3 (0<=x<=0.3) polycrystalline films prepared by spray pyrolysis. The virgin La0.7Ca0.3MnO3 (LCMO) (x=0.0) film shows paramagnetic-ferromagnetic [insulator-metal (IM)] transition at TC∼260 K (TIM∼245 K). Ag doping induces appreciable enhancement in TC/TIM and interestingly TIM of Ag doped films is higher than the corresponding TC value. In the 30% Ag doped film IM transition occurs at ∼325 K which is ∼10 K higher than its TC∼315 K. Strong irreversibility is observed in zero field cooled–field cooled magnetization of all the films and the irreversibility temperature Tirr>TC increases with Ag doping. This suggests the formation of magnetic clusters above TC. The pure LCMO film exhibits small magnetoresistance (MR) ∼20% and rather poor temperature coefficient of resistance (TCR) in the vicinity of the room temperature. In contrast, around room temperature the Ag doped films show large MR which is ∼60% for x=0.15 and decreases to ∼30% for the pure Ag doped film. Ag doped films also have good TCR ∼4%/K in the vicinity of room temperature. [ABSTRACT FROM AUTHOR]

We report synthesis, structural details and magnetization of SmFe1-xCoxAsO with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe site in SmFeAsO in an iso-structural lattice with slightly compressed cell. The parent compound exhibited known spin density wave (SDW) character below at around 140 K. Successive doping of Co at Fe site suppressed the SDW transition for x = 0.05 and later induced superconductivity for x = 0.10, 0.15 and 0.20 respectively at 14, 15.5 and 9K. The lower critical field as seen from magnetization measurements is below 200Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co i.e. x = 0.30. Clearly the Co substitution at Fe site in SmFe1-xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes non-superconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mobile electrons to the system and superconductivity appears, however direct substitution introduces simultaneous disorder in superconducting FeAs layer and thus superconductivity disappears for higher content of Co. [ABSTRACT FROM AUTHOR]

One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe1/2Te1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a=3.8015(2) and c =6.0280(4) Å. Magnetization measurements indicated bulk superconductivity with lower critical field (Hc1) of around 180 Oe. By applying Ginzburg-Landau theory, the Hc2(0) value is estimated to be ∼1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at Tc near 13 K and an expected decrease in the same was observed under an applied magnetic field. [ABSTRACT FROM AUTHOR]

We report synthesis, structure, electrical transport, and heat capacity of SmFeAsO. The title compound is synthesized by one-step encapsulation of stoichiometric FeAs, Sm, and Sm2O3 in an evacuated (10-5 Torr) quartz tube by prolong (72 h) annealing at 1100 °C. The as-synthesized compound is crystallized in tetragonal structure with P4/nmm space group having lattice parameters a=3.937 26(33) A and c=8.498 02(07) A. The resistance (R-T) measurements on the compound exhibited ground state spin-density-wave (SDW)-like metallic steps below 140 K. Heat capacity CP(T) measurements on the title compound, showed an anomaly at around 140 K, which is reminiscent of the SDW ordering of the compound. At lower temperatures the CP(T) shows a clear peak at around 4.5 K. At lower temperature below 20 K, Cp(T) is also measured under an applied field of 7 T. It is concluded that the CP(T) peak at 4.5 K is due to the antiferromagnetic ordering of Sm3+ spins. These results are in confirmation with ordering of Sm in Sm2-xCexCuO4. [ABSTRACT FROM AUTHOR]

The perovskite Sr1-xHoxCoO3-δ shows room temperature ferromagnetism (Tc∼335 K) in a severely limited composition range 0.2<=x<=0.25. The formal Co valence is almost constant at +3 regardless of the Ho concentration (x>=0.2); thus, the high-spin state or the intermediate spin state of 3d6 Co should be mainly responsible for the magnetism. The ferromagnetism was found to accompany the formation of a superstructure 2ap×2ap×4ap (ap denotes a cubic perovskite cell). Besides, an additional superstructure 4(2ap)×4(2ap)×(4ap) was found at x=0.225, where the ferromagnetic volume in magnetic susceptibility was largest. The data suggest that the formation of the multiple superstructures probably plays a key role to establish the peculiar ferromagnetism. [ABSTRACT FROM AUTHOR]

The superconducting ruthenocuprates RESr2Cu2RuO8 (where RE is a rare earth or Y) have been interpreted as ferromagnetic superconductors, based on a strong response to applied field at the Ru Néel temperature (around 130 K). However, neutron diffraction measurements on the Gd compound by Lynn et al. [Phys. Rev. B 61, 1214964 (2000)] (using a separated isotope) show evidence only of antiferromagnetic order, while very limited data by Takagiwa et al. [J. Phys. Soc. Jpn. 70, 333 (2001)] on the Y compound show one antiferromagnetic Bragg peak and possible coexisting ferromagnetism. We have studied a sample of YSr2Cu2.1Ru0.9O7.9 prepared by a high pressure-high temperature route. Temperature dependent neutron powder diffraction shows antiferromagnetic order, manifested by the observation of the 12, 12, 12 and 12, 12, 32 reflections, which appear at 135 K [as suggested by the superconducting quantum interference device (SQUID) data]. Their intensities at the lowest temperature are consistent with a c-axis orientation of the Ru magnetic moments. Although the lowest order nuclear Bragg peak shows a small intensity increase as the temperature is lowered, this is attributed to magnetic ordering of the Cu planes and not to the presence of a ferromagnetic component, in agreement with the polarized neutron data of Lynn et al. [Phys. Rev. B. 61, 1214964 (2000)] Magnetic resonance and SQUID data on the same sample (to be reported elsewhere) show a complex picture, associated with Cu magnetic ordering. [ABSTRACT FROM AUTHOR]

We investigated the third harmonic nonlinear susceptibility of the Ru0.9Sr2YCu2.1O7.9 magnetosuperconductor and found the presence of two well separated negative peaks. The peak at TM=140 K is connected to the previously well known main magnetic ordering of the Ru sublattice, and the peak at around 180 K is probably associated with the formation of superparamagnetic particles above TM. The negative signals for both peaks will be discussed in terms of ensuing magnetic orderings of Ru spins at these temperatures. Further, these results will be compared with a recent study of nonlinear susceptibility on RuSr2GdCu2O8. [ABSTRACT FROM AUTHOR]

RuSr2(LnCe2(Cu2O12.25 (Ru-1232) compounds with Ln=Y and Dy being synthesized by high pressure high temperature (6 GPa, 1200 °C) solid state synthesis route crystallize in space group P4/mmm in near single phase form with small quantities of SrRuO3 and RuSr2(RE1.5Ce0.5)Cu2O10 (Ru-1222). Both samples exhibit magnetic transitions (Tmag) at ~90 K with significant branching of zero-field-cooled (ZFC) and field-cooled (FC) magnetization and a sharp cusp in ZFC at ~70 K, followed by superconducting transitions at ~30 K. Both compounds show typical ferromagnetic hysteresis loops in magnetic moment (M) versus field (H) magnetization right up to Tmag. i.e., <90 K. To our knowledge these are the first successfully synthesized Ru-1232 compounds in near single phase with lanthanides including Y and Dy. The results are compared with widely reported Gd/Ru-1222 and Ru-1212 sRuSr2GdCu2O8d compounds. In particular, it seems that the Ru moments magnetic ordering temperature (Tmag) scales in the c-direction distance between magnetic RuO6 octahedras in Ru-1212/1222 or 1232 systems. [ABSTRACT FROM AUTHOR]

NMR measurements have been performed on the ordered perovskite Sr2Cu(Re0.69Ca0.31)O6 which shows ferromagnetic (ferrimagnetic) properties below Tc∼440 K with spontaneous magnetization of about 0.25 μB per formula unit at 5 K. Two kinds of NMR lines showing large enhancement of NMR signals were observed at 5 K with H=0.5 T at the frequency range from 58 to 180 MHz, and each line was attributed to the Cu1 and Cu2 site. [Copyright &y& Elsevier]

We have performed detailed ac susceptibility measurements to investigate the vortex dynamics in a Ca10(Pt3As8)[(Fe1-xPtx)2As2]5 single crystal as a function of temperature, frequency, ac amplitude, and dc field. The field dependence of the activation energy U is derived in the framework of thermally activated flux creep theory, yielding a power law dependence of U ~ Hɑ with ɑ ≈ -1.0 for H above 0.30 T, while below 0.3 T U is independent of the field. The activation energy reaches 104K at low fields, suggesting strong pinning in the material. The nonlinear function of the activation energy vs. the current density is determined, which shows logarithmic dependence U(J) ∞ lnJ. [ABSTRACT FROM AUTHOR]

Highlights: [•] The detailed P–T phase diagram of BiMnO3 was established. [•] We found three monoclinic modifications of BiMnO3 at pressure and temperature. [•] A suppression of monoclinic C2/c phase have been observed under pressure. [•] We found a new orthorhombic Imma phase of BiMnO3 at P >20GPa. [Copyright &y& Elsevier]

Highlights: [•] Flux jumps were observed inpoly-crystalline Ba0.5K0.5Fe1.9 M 0.1As2 (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. [Copyright &y& Elsevier]

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]

We investigated magnetic domain structures of a multiferroic manganite, BiMnO3, by Lorentz transmission electron microscopy. Ferromagnetic domains were observed below ∼105 K, close to the ferromagnetic Curie temperature, TC. The spontaneous magnetization aligns distinctly along the [010] direction, suggesting that the magnetic easy direction is along the b axis. Inflection and merging of the domain walls was observed at twin boundaries. This indicates pinning of the magnetic domain walls at crystallographic twin boundaries. Furthermore, we observed narrow magnetic domain walls, suggesting strong magnetocrystalline anisotropy. [ABSTRACT FROM AUTHOR]

X-ray near edge absorption spectroscopy was used to probe the electronic structure of multiferroic orthorhombic LuMnO3 polycrystalline samples and strained, twin-free orthorhombic (1-10) LuMnO3 films grown by pulsed laser deposition on (1-10) YAlO3 substrates. For all o-LuMnO3 samples x-ray near edge absorption spectroscopy spectra reveal that the pre-edge structure is influenced by the increase in MnO6 distortion as a result of the smaller Re-ion or film strain. Furthermore there is clear evidence of anisotropic Mn-O bonding and Mn orbital ordering along the c- and [110] direction. The experimental film and bulk data are in agreement with ab initio simulations. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the crystal structure and transport properties of the new cobalt oxide (CaOH)1.14CoO2. The compound has the layer structure, which consists of CdI2-type CoO2 layers and rock-salt-type double CaOH atomic layers. The two subcells have incommensurate periodicity along the a-axis, resulting in a modulated crystal structure due to the inter-subcell interaction. The structural modulation affects carrier conduction through the potential randomness. We found that the two-dimensional (2-D) variable-range-hopping-type hole conduction is dominant at low temperature. [Copyright &y& Elsevier]

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]

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: We have studied crystal structure and transport properties of the quasi one-dimensional cobalt oxide CaCo2O4. The CaCo2O4 phase crystallizes in calcium-ferrite type structure, which consists of a corner- and edge-shared CoO6 octahedron network including one-dimensional double chains. Large thermoelectric power (S ∼150μV/K at 390K) with metallic temperature dependence of S, moderate resistivity (ρ ∼2.9×10−1 Ωcm at 390K) with carrier localization at low temperature, and normal thermal conductivity (κ ∼6.3W/Km at 390K) were observed. The phonon mean-free path was calculated from the observed data, as a function of temperature. The long phonon mean-free path (l ∼24Å at 300K) implies that the thermal conductivity could be suppressed by impurity scattering of phonons with partial element substitution. [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]