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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 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 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]

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]

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]

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]

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]

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]

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: 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]

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]

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]

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]

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]

Abstract: The nuclear quadrupole resonance (NQR) frequency of Co nuclei and the nuclear spin–lattice relaxation rate were measured on several bilayered hydrate (BLH) () with variety of superconducting (SC) and magnetic transition temperatures, and , together with non-SC mono-layered hydrate (MLH) (). In the high temperature region above 70K, in all the samples follows the same temperature dependence which is interpreted as the pseudogap behavior. In the BLH compounds, increases with decreasing temperature below 70K, and the values of at are large in high- samples. The magnetic ordering is ascertained from the observation of the prominent divergence of at in the samples whose NQR frequency is higher than 12.5MHz. The temperature dependence of is found to be consistently expressed by a unique function with two fitting parameters. We analyze the temperature dependence of on the basis of this function, and investigate the relationship between the magnetic fluctuations and superconductivity in the BLH compounds. [Copyright &y& Elsevier]

Abstract: Nuclear quadrupole frequency (ν Q ) and spin-lattice relaxation rate 1/T 1 of Co were measured on various bilayered hydrate (BLH) Na x CoO2 · yH2O (y ∼1.3) with different values of superconducting (SC) and magnetic-transition temperatures, T c and T M, together with non-SC monolayered hydrate (MLH) Na x CoO2 · yH2O (y ∼0.7). In the temperature range above 70K, 1/T 1 T in all samples follows the similar temperature dependence as each other. In the BLH compounds, 1/T 1 T is enhanced with decreasing temperature below 70K, and the values of 1/T 1 T at T c are larger in the higher-ν 3 sample, where ν 3 is the peak frequency of the NQR spectrum arising from ±5/2↔±7/2 transitions. The magnetic ordering is indicated from the prominent divergence of 1/T 1 T at T M and the presence of the internal field at the Co nuclear site in the samples with ν 3 higher than 12.5MHz. We analyze the temperature dependence of 1/T 1 T in all samples on the basis of identical formula, and discuss the relationship between magnetic fluctuations and superconductivity in the BLH cobaltate. [Copyright &y& Elsevier]

Abstract: We report the phase formation, and present a detailed study of magnetization and resistivity under magnetic field of MgB2 polycrystalline bulk samples prepared by the Fe-tube encapsulated and vacuum (10−5 Torr) annealed (750 ∘C) route. Zero-field-cooled magnetic susceptibility measurements exhibited a sharp transition to the superconducting state with a sizeable diamagnetic signal at 39 K . The measured magnetization loops of the samples, despite the presence of flux jumps, exhibited a stable current density of around 2.4×105 A/cm2 in up to 2 T (Tesla) field and at temperatures up to 10 K. The upper critical field is estimated from resistivity measurements in various fields and shows a typical value of 8 T at 21 K. Further, measurements at an applied field of 0.1 T reveal a paramagnetic Meissner effect (PME) that is briefly discussed. [Copyright &y& Elsevier]

Abstract: We carefully studied the nonsuperconducting sample of the magneto-superconducting RuSr2(Eu1−x Ce x )Cu2O10−δ series with composition RuSr2EuCeCu2O10−δ . This compound seems to exhibit a complex magnetic state as revealed by host of techniques like resistivity, thermopower, magnetic susceptibility, and MR measurements. The studied compound exhibited ferromagnetic like M(H) loops at 5, 20, and 50K, and semiconductor like electrical conduction down to 5K, with −MR 7T of up to 4% at low temperatures. The −MR 7T decreases fast above 150K and monotonically becomes close to zero above say 230K. Below, 150K −MR 7T decreases to around 3% monotonically down to 75K, with further increase to 4% at around 30K and lastly having a slight decrease below this temperature. The thermopower S(T) behavior closely followed the −MR 7T steps in terms of d(S/T)/dT slopes. Further, both MR 7T steps and d(S/T)/dT slopes are found in close vicinity to various magnetic ordering temperatures (T mag) of this compound. [Copyright &y& Elsevier]

In order to investigate the role of the water molecules in Na0.35CoO2 · 1.3H2O, we synthesized superconducting Na0.35CoO2 · 1.3H2O and nonsuperconducting Na0.35CoO2 · 0.7H2O, and measured their normal-state magnetic susceptibilities. The susceptibility of Na0.35CoO2 · 1.3H2O has an enhancement below ∼150 K probably caused by ferromagnetic fluctuation, whereas no such enhancement was observed in Na0.35CoO2 · 0.7H2O. The water molecules in Na0.35CoO2 · 1.3H2O may work to shield random coulomb potential of the Na ions with smoother potential at the CoO2 layer. This effect may account for the appearance of superconductivity in Na0.35CoO2 · 1.3H2O. [Copyright &y& Elsevier]

RuY1.5Ce0.5Sr2Cu2O10, is not superconducting (SC) and orders magnetically at TM=152 K. The Ru moment at 5 K is 0.75μB. Ferromagnetic hysteresis loops are observed below Tirr=100 K. At 100 K, the remanent magnetization (Mrem) and the coercive field (HC) become zero. Surprisingly, at Tirr a reappearance of antiferromagnetic (AFM) hysteresis loops are observed with a peak at 120 K for both Mrem and HC. The paramagnetic constants are: Peff=2.06μB (greater than the 1.73μB expected for low spin Ru5+) and θ=136 K which agrees well with TM. Substitution of Zn (2.5% atm.) for Cu in RuEu1.5Ce0.5 Sr2Cu2O10 (TC=38 K), suppresses TC but does not affect the magnetic features such as: TM and Tirr, Mrem and HC. This indicates that both SC and magnetic states are practically decoupled.We argue that the magnetic structure of this system becomes (i) AFM ordered at TM. (ii) Due to the tilting of the RuO6 octahedra away from the crystallographic c-axis, at Tirr, weak-ferromagnetic (W-FM) order is induced by the canting of the Ru moments. (iii) At TC (TM/TC∼4), the specific materials (M=Eu, Gd) become SC. Below TC, both SC and W-FM states coexist. [Copyright &y& Elsevier]

A Tb-123 phase with the composition, TbSr2Cu2.7Mo0.3O7+δ, has been synthesized in single-phase form by the solid-state reaction route. Its phase purity has been confirmed from neutron powder diffraction studies. The as-synthesized Tb-123 sample does not show superconductivity down to 5 K. On the other hand, an unusually high antiferromagnetic ordering temperature (TN) of around 7 K is seen for the Tb moments. After 120-atm-O2 post-annealing, bulk superconductivity is achieved in this compound with a superconducting transition temperature (Tc) of about 30 K, without any significant effect on TN. To achieve higher oxygen content and higher Tc, the as-synthesized sample was subjected to high-pressure oxygenation, carried out in a closed cell, at 5 GPa and 400 °C in the presence of AgO as an excess-oxygen source. This sample exhibited superconductivity onset at around 80 K with a Meissner fraction larger than 10% at 5 K. Our observation of superconductivity at 80 K is the highest Tc to-date for the Tb-123 type compounds. [Copyright &y& Elsevier]

Single crystals of Au1+xBa2Ca2Cu3−xO9 (Au-1223) were grown at 6 GPa and 1325 °C. This phase is the third member of the Au-containing cuprate family of AuBa2Can−1CunO2n+3 and shows a weak signal of superconductivity. The crystal structure was refined to R1 (I>2σ(I))=0.0188 and wR2=0.0485 with F2 data. The Au-1223 phase crystallizes in the space group Pmmm (no. 47), a=3.8119(1) A˚, b=3.8556(1) A˚, c=15.4431(5) A˚, Z=1. Partial substitution of Au for Cu in the CuO2 planes was revealed. The Au incorporation to the conduction layers may be a reason for the suppression of superconductivity in Au-1223. [Copyright &y& Elsevier]

Single crystals were grown for new layered oxycarbonates CCa2CuO5 and CSr1.9Ca1.1Cu2O7 at 6 GPa using a belt-type apparatus. Their crystal structures were determined using single crystal X-ray diffraction data with R1(wR2)=0.0294(0.0659) and 0.0199(0.0457) for CCa2CuO5 and CSr1.9Ca1.1Cu2O7, respectively. These phases crystallize in the space group P4/mmm (No. 123), Z=1 with a=3.8157(1) A˚, c=7.1426(3) A˚ for CCa2CuO5 and a=3.8753(1) A˚, c=10.6765(5) A˚ for CSr1.9Ca1.1Cu2O7. In contrast to CSr2CuO5, no ordering in the orientation of the triangular CO3 groups was revealed in CCa2CuO5 and CSr1.9Ca1.1Cu2O7. [Copyright &y& Elsevier]

Abstract: Pt doped 122 iron arsenide SrFe1− x Pt x As2 (0⩽ x ⩽0.4) was successfully synthesized. The tetragonal unit-cell volume and the lattice constant a increase with increasing the Pt content, while c decreases, suggesting that the Fe ions are indeed replaced by Pt ions. By the Pt doping, the magnetic order of the parent phase is suppressed, and superconductivity emerges at approximately x =0.15. T c reaches the maximum of 16K at x =0.2. The compounds series can be a suitable subject to investigate role of the doped 5d state in the superconducting 3d Fe–As layer. [Copyright &y& Elsevier]

Abstract: We performed Co nuclear quadrupole resonance (NQR) measurements on bilayered hydrate cobaltate . The sample we used demonstrates a magnetic transition at , which is observed from susceptibility, nuclear spin-lattice relaxation rate, and NQR spectrum measurements. We observed inhomogeneous broadening of the NQR spectrum below . In order to interpret the internal field distribution, we numerically solved a nuclear-spin Hamiltonian including the nuclear quadrupole interaction and the Zeeman interaction, and estimated the internal fields from the observed Co-NQR spectrum. It is considered that the internal fields possess weak modulation. The obtained internal-field distribution suggests the occurrence of the spin-density-wave ordering. [Copyright &y& Elsevier]

Abstract: FeSr2EuCu2O8 (FeEu-1212) does not exhibit superconductivity when prepared by classical solid state route, because of iron atoms substitute partially copper atoms in the superconductive CuO2 planes. Recently, it has been found that high temperature annealing in Ar or N2 can favour the complete substitution of copper in CuO1−δ chains instead of in the CuO2 planes. After this annealing, the total oxygen content of the tetragonal FeSr2RECu2O8 decreases and the crystal structure changes to orthorhombic. It is possible to get superconductivity with a second annealing in O2 at low temperature. In this work a different approach was tried for first time. The samples of FeSr2EuCu2O8−δ series with δ =0, 0.5, 0.75 and 1 were prepared by high pressure high temperature (HPHT) synthesis starting from a mixture of Fe2O3, SrO2, Eu2O3, CuO and Cu. The final oxygen content was determined by the ratio between CuO and Cu. The structure of thus prepared samples changed from tetragonal for δ =0 to orthorhombic for δ =0.75 and 1. The iron atoms selectively occupy the CuO1−δ chains, if the oxygen content is low. Superconductive properties of these materials were studied, by subjecting them to high pressure and low temperature annealing with Ag2O2 or KClO4 as oxidizing agents. [Copyright &y& Elsevier]

Abstract: The three first members of the Cr-12s2 (s =1,2,3) homologous series, i.e. CrSr2YCu2O8 (Cr-1212), CrSr2(Y1.5Ce0.5)Cu2O10 (Cr-1222) and CrSr2(Y1Ce2)Cu2O12(Cr-1232) are synthesized by high pressure high temperature (HPHT) 6GPa and 1550°C process. Though the Cr-1212 and Cr-1232 could not be formed in single phase with full Cr, the Cr-1222 is achieved in pure phase with space group I4/mmm. These compounds belong to the multi-layered copper oxides series that differ from each other only in terms of the (Ce,Y)-[O2-(Ce,Y)] s−1 layer blocks between two identical CuO2 planes with s =1, 2 and 3. At 5K, the magnetization M(H) experiments showed some ferromagnetic like hysteresis loops though the characteristic M r and H c were not seen clearly. None of the studied compounds exhibited superconductivity down to 5K. [Copyright &y& Elsevier]

Abstract: Low-temperature specific-heat data C(T) of two Na0.35CoO2. 1.3H2O samples (I and II) with temperature T down to 0.6K without and with magnetic field of 8T are presented. The normal-state linear coefficient of specific heat γ n, Debye temperature Θ D, superconducting transition temperature T c, specific heat jump at T c, ΔC/γnsT c, and superconducting volume of fraction (SVF) are 14.89mJ/molK2, 503, 4.7K, 1.96, and 26.6% for sample I and 13.94mJ/molK2, 362, 4.5K, 1.45, and 47.4% for sample II, respectively. Because the superconducting properties may depend on the water content of sample, it is found that the better quality (higher SVF) of sample, the nodal order parameter is better than BCS isotropic s-wave model in describing the gap function of this interesting compound Na0.35CoO2. 1.3H2O. [Copyright &y& Elsevier]

Abstract: We measured -NMR spectra and nuclear spin-lattice relaxation rates ) of superconducting and non-superconducting bilayer hydrates , ). The central resonance frequencies show small but various shifts due to differences in the shielding effect by intercalated molecules. The different shielding effect also gives a large difference in the magnitude of . [Copyright &y& Elsevier]

Abstract: We have performed Co nuclear quadrupole resonance (NQR) measurements in various bilayered-hydrate (BLH) compounds, showing superconducting (SC) and non-SC characteristics. A weak magnetic order was found in a BLH sample with a longer -axis lattice parameter. We also found that the NQR frequency arising from the transition is related to the ground state of this system. A phase diagram is developed, in which the superconducting and magnetic-order temperature and are plotted with respect to . [Copyright &y& Elsevier]

Abstract: The field-swept nuclear magnetic resonance (NMR) spectra of 59Co in the superconductor have been measured at several magnetic fields below . The anisotropic Knight shift seems to decrease with decreasing temperature without broadening of the spectrum, indicating either the site-selective diamagnetic effect, which may result in the spin-triplet superconductivity, or the decrease of the intrinsic spin shift. Analysis of the magnetic field dependence of the Knight shift at 2K revealed that the superconductivity occurs in an unconventional way. [Copyright &y& Elsevier]

Abstract: The Fe-rich NiAs-type antimonide Fe1.5Sb was synthesized by a high-pressure method and its magnetic properties were investigated. The compound shows a manifest dropt at ∼55K in magnetic susceptibly vs. temperature curves under the zero-field and the field cooling conditions, being likely due to a spin glass-like transition rather than a superconducting transition. The high magnetic transition temperature reflects the highest Fe concentration achieved to date in the iron antimonide. [ABSTRACT FROM AUTHOR]

Abstract: The effect of ruthenium (Ru) doping in SmFe1− x Ru x AsO (x =0.0–0.50) compound is studied here. The samples synthesized are mostly phase pure and not contaminated with various FeAs phases. It is found that with increasing Ru concentration x, the system turns from weak ferromagnetic (spin density wave (SDW)) to ferromagnetic state at x =0.20–0.30 without any sign of superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: We report on the result of muon spin relaxation measurements in a deuterated specimen of cobalt oxyhydrate superconductor, , which exhibits a hysteresis resembling ferromagnetic order in magnetic susceptibility. While the possibility of bulk ferromagnetic order is eliminated by the absence of spontaneous muon precession signal under zero field, the spectra indicate the appearance of magnetic domains below in accordance with a hysteresis in the susceptibility. This correlation demonstrates strong coupling between the water layers and the electronic state of CoO2 layers. [Copyright &y& Elsevier]