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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]

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]

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]

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: 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]

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]

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]

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 enhancement of the critical current density (J c(H)) of carbon and nano-SiC doped MgB2 is presented and compared. The upper critical field (H c2) being determined from resistivity under magnetic field experiments is though improved for both C substitution and nano-SiC addition the same is more pronounced for the former. In MgB2− x C x carbon is substituted for boron that induces disorder in the boron network and acts as internal pinning centres. The optimal J c(H) values are obtained for x =0.1 sample. In case of nano-SiC doped in MgB2, the J c(H) improves more profoundly and two simultaneous mechanisms seems responsible to this enhancement. Highly reactive nano-SiC releases free carbon atom, which gets easily incorporated into the MgB2 lattice to act as intrinsic pinning centres. Further enhancement is observed for higher nano-SiC concentrations, where the un-reacted components serve as additional extrinsic pinning centres. [Copyright &y& Elsevier]

Abstract: The synthesis and characterization of PVA (Poly Vinyl Acetate) doped bulk MgB2 superconductor is reported here. PVA is used as a carbon source. PVA doping effects made two distinguishable contributions: first enhancement of J c field performance and second an increase in H c2 value, both because of carbon incorporation into MgB2 crystal lattice. The susceptibility measurement reveals that T c decreased from 37 to 36K. Lattice parameter ‘a’ decreased from 3.085Å to 3.081Å due to the partial substitution of carbon at boron site. PVA doped sample exhibited the J c values greater than 105 A/cm2 at 5 and 10K at low fields; which is almost 3 times higher than the pure one, while at high fields the J c is increased by an order of magnitude in comparison to pure MgB2. From ρ(T)H measurements we found higher T c values under magnetic field for doped sample; indicating an increase in H c2. Also the magnetization measurements exhibited a significant enhancement in H irr value. The improved performance of PVA doped MgB2 can be attributed to the substitution of carbon at boron site in parent MgB2 and the resulting impact on the carrier density and impurity scattering. The improved flux pinning behavior could easily be seen from reduced flux pinning force plots. [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: Detailed X-ray diffraction studies on RuSr2Eu1.5Ce0.5Cu2O10−δ (Eu–Ru-1222) magneto superconductor down to 13K at close temperature intervals revealed that with decreasing temperature, the c-parameter decreases linearly down to 100K, following the relation c =28.412(1)+2.5(1)×10−4 T and then becomes almost temperature independent on further lowering of temperature. Interestingly, the linear decrease in the a-parameter is seen only up to 180K. Below 180K, the observed values of the a-parameters are more than the value expected from the linear variation. This departure can be considered as development of strain in the system. Interestingly enough, these temperatures coincide with the complex magnetic ordering (T mag) of Ru in Ru-1222 system. This is the first report of the observation of the onset of excess volume and also of the strain along the a-axis near the magnetic ordering temperature in Ru-1222 superconductor, and indicates a coupling between the lattice and the magnetism in this system. Magnetization, magneto transport and thermoelectric power measurements being carried out on the same sample are also reported. The results of low temperature excess volume and the strain along a-axis of Ru-1222 compound are reportedly not seen in Ru-1212 (RuSr2GdCu2O8). [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]

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]

Modulation structures of Bi2Sr2(RE1−xCex)2Cu2O10+y (RE: Y, Nd, Sm and Gd) were investigated by means of high-resolution electron microscopy and electron diffraction. We proved that this system’s modulation structure is characterized by the displacement of atomic positions, as in other Bi-system high-TC superconductors. Superlattice spots due to the modulation structures in electron diffraction showed that the incommensurate modulation wave vector was q=(0,2/(9−ϵ),1/2). The ϵ changed with the average ionic radii of rare earth ions, Ce substitution (x), and excess oxygen content (y). [Copyright &y& Elsevier]

Two new layered oxyborates B2Sr3.2Y1.8Cu3O12 and B2Sr3.11Ho1.89Cu3O12 have been synthesized at 6 GPa using a belt-type apparatus. These compounds could be described as intergrowth between B-1201 and B-1212 phases. The crystal structure of B2Sr3.11Ho1.89Cu3O12 has been determined using single crystal X-ray data. It was refined to R1(I>2σ(I))=0.0456, wR2(all data)=0.1044 with F2 data. B2Sr3.2Y1.8Cu3O12 and B2Sr3.11Ho1.89Cu3O12 crystallize in the space group P4/mmm (no. 123), Z=1 with a=3.852(1) A˚, c=17.770(6) A˚ and a=3.8516(4) A˚, c=17.764(2) A˚, respectively. A weak superstructure with as=a√2, bs=b√2, cs=c was deduced from an electron diffraction pattern for B2Sr3.11Ho1.89Cu3O12 probably due to local ordering of the triangular BO3 groups although such ordering was not revealed from single crystal X-ray data. [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: Thermal effect on the orthorhombic crystal structure (Cmcm) of the correlated 4d post-perovskite CaRhO3 was investigated by an X-ray powder diffraction method between 60K and 300K. Anisotropic thermal evolution of the structure was observed over the temperature range, and in addition, an anomalous change of the lattice parameters was detected at the antiferromagnetic transition temperature of 90K, indicating possible correlations between the lattice and the magnetic order. [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 report properties of the Zn-substituted polycrystalline superconductors BaFe1.87− x Zn x Co0.13As2 (x =0, 0.04, 0.06 and 0.08) prepared at ambient pressure condition. Electrical conductivity and magnetization measurements revealed that the superconductivity is suppressed by at most 2% substitution of Zn, which shows typical behavior of an anisotropically gaped superconductivity rather than an isotropically gaped superconductivity. With increasing the amount of Zn, weak change in superconductivity was observed. It is likely impossible to obtain BaFe1.87− x Zn x Co0.13As2 crystals with x >0.04 at ambient pressure condition. On the basis of the structural and the physical properties of the present system, we discuss a possible mechanism of the superconducting pairing. [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]

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]

Abstract: Oxygen vacant superconductors LaFeAsO1− δ were synthesized under a high-pressure condition. A bell-shaped feature in Tc vs. δ was observed for LaFeAsO1− δ as well as TbFeAsO1− δ . The optimized Tc was achieved at δ of 0.15, being comparable with that for TbFeAsO1− δ . The relatively wide δ window of LaFeAsO1− δ may merit scientific and technical studies of high-Tc superconductivity. [ABSTRACT FROM AUTHOR]

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]