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Discusses the results on structural aspects, magnetic, and superconducting properties of the La1-xPrxBaCaCu3O7 system. Observation of high temperature superconductivity above 90K in all rare earth (RE) based REBa2Cu3O7 compounds; Information on the structure of RE based 123 perovskite compound.

Reports on details of the structural and magnetic properties of RSFO compounds with R=Y, lathanum (La), praseodymium (Pr), and gagolinium (Gd). Information on the discovery of high Tc superconductivity; Observation of a unique behavior of PrBa2Fe3 in terms of magnetic and thermal properties.

The magneto-transport and magnetocaloric effect in Pr 2/3 Sr 1/3 MnO 3 :Ag 2 O (PSMO:Ag) with Ag 2 O (10–30 mol%) have been studied by resistivity and magnetization measurements. Temperature coefficient of resistance (TCR), magneto-resistance (MR) and magnetocaloric properties of the composite have shown different responses to Ag addition. Rietveld refinement confirms single phase crystalline structure with orthorhombic Pbnm space group and presence of silver metal as well. TCR changes randomly with Ag, increasing initially to 7.8% K −1 for PSMO:Ag10 composite which then decreases marginally with increasing Ag content. MR has been found to reach a maximum value of 30.5% at 1 T applied field for PSMO:Ag10 composite. Magnetic entropy change (Δ S M ) increases with increasing Ag content and is found to be 3.5 J kg −1 K −1 (1 T), 6.1 J kg −1 K −1 (2 T) and 8.4 J kg −1 K −1 (3 T) for PSMO:Ag30 composite at 285 K. The maximum refrigeration capacity of 39.5 J kg −1 (1 T), 91.0 J kg −1 (2 T) and 107.7 J kg −1 (3 T) has been found for the PSMO:Ag20 composite. PSMO:Ag composite exhibits potential for bolometric, magnetic sensing and magnetic refrigerating applications near room temperature. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of Se doped Bi4O4S3 superconductor. [•] Bulk superconductivity is confirmed at below 4.5K. [•] Se doping suppresses superconductivity in Bi4O4S3 superconductor. [ABSTRACT FROM AUTHOR]

Abstract: We present detailed magnetization and magneto-transport studies on the title compound SmCoAsO. In a recent paper we reported (Awana et al., 2010 ) the complex magnetism of this compound. SmCoAsO undergoes successive paramagnetic (PM)–ferro-magnetic (FM)–anti-ferro-magnetic (AFM) transitions with decrease in temperature. This is mainly driven via the c-direction interaction of Sm4f (SmO layer) spins with adjacent (CoAs layer) ordered Co3d spins. In this article we present an evidence of kinetic arrest for FM–AFM transition. The isothermal magnetization (MH) loops for SmCoAsO exhibited the meta-magnetic transitions at 6, 8 and 10K at around 80, 60 and 50kOe fields, respectively, with characteristic hysteresis shoulders along with the non-zero moment at the origin, thus suggesting the possibility of kinetic arrest. Suggested kinetic arrest is further evident in zero field-cooled (ZFC) and field-cooled (FC) hysteresis under high fields of up to 140kOe magnetization (MT) and the magneto-transport measurements R(T)H during FM–AFM transition. The time dependent moment experiments exhibited very small (∼2–3%) increase of the same below 20kOe and decrease for 30kOe at 15K. [Copyright &y& Elsevier]

Abstract: Here, we report the synthesis and characterization of sulphur-substituted iron telluride i.e. FeTe1− x S x ; (x =0–30 %) system and study the impact of low temperature oxygen (O2) annealing as well. Rietveld analysis of room temperature X-ray diffraction (XRD) patterns shows that all the compounds are crystallized in a tetragonal structure (space group P4/nmm) and no secondary phases are observed. Lattice constants are decreased with increasing S concentration. The parent compound of the system i.e. FeTe does not exhibit superconductivity but shows an anomaly in the resistivity measurement at around 78K, which corresponds to a structural phase transition. Heat capacity C p(T) measurement also confirms the structural phase transition of FeTe compound. Superconductivity appears by S substitution; the onset of superconducting transition temperature is about 8K for FeTe0.75S0.25 sample. Thermoelectric power measurements S(T) also shows the superconducting transition at around 7K for FeTe0.75S0.25 sample. The upper critical fields Hc 2(10%), Hc 2(50%) and Hc 2(90%) are estimated to be 400, 650 and 900 kOe respectively at 0K by applying Ginzburg Landau (GL) equation. Interestingly, superconducting volume fraction is increased with low temperature (200°C) O2 annealing at normal pressure. Detailed investigations related to structural (XRD), transport [S(T), R(T)H], magnetization (AC and DC susceptibility) and thermal [C p(T)] measurements for FeTe1− x S:O2 system are presented and discussed. [Copyright &y& Elsevier]

Abstract: We report the synthesis, magnetic susceptibility and crystal structure analysis for samples. The study helps find a correlation among the lattice parameters, chemical composition and the superconducting transition temperature . Rietveld analysis is done on the -ray diffraction patterns of all synthesized samples to determine the lattice parameters. The parameter decreases slightly and has a random variation with increasing , while parameter increases from 3.26 for pure NbB2 to 3.32 for i.e. NbB2.4. With higher Boron content the parameter decreases slightly. The stretching of lattice in direction induces superconductivity in the non-stoichiometric niobium boride. Pure NbB2 is non-superconductor while the other samples show diamagnetic signal in the temperature range 8.9–11 K. Magnetization measurements () at a fixed temperature of 5 K are also carried out in both increasing and decreasing directions of field. The estimated lower and upper critical fields ( & ) as viewed from plots are around 590 and 2000 Oe, respectively, for NbB2.6 samples. In our case, superconductivity is achieved in NbB2 by varying the Nb/B ratios, rather than changing the processing conditions as reported by others. [Copyright &y& Elsevier]

Abstract: We report the synthesis and variation of superconductivity parameters such as transition temperature , upper critical field , critical current density , irreversibility field and flux pinning parameter for the MgB2−x C x system with nano-carbon doping up to . Carbon substitutes successfully on boron site and results in significant enhancement of and . Resistivity measurements reveal a continuous decrease in under zero applied field, while the same improves remarkably at higher fields with an increase in nano-carbon content for MgB2−x C x system. The irreversibility field value is 7.6 and 6.6 T at 5 and 10 K respectively for the pristine sample, which is enhanced to 13.4 and 11.0 T for sample at same temperatures. Compared to undoped sample, critical current density for the nano-carbon-doped sample is increased by a factor of 24 at 10 K at 6 T field. [Copyright &y& Elsevier]

Abstract: The physical property characterization of Al doped Mg1− x Al x B2 system with x =0.0 to 0.50 is reported. The results related to phase formation, structural transition, resistivity ρ(T) and magnetization M(T) measurements are discussed in detail. It is shown that the addition of electrons to MgB2 through Al results in loss of superconductivity. Also seen is a structural transition associated with the collapse of boron layers reflected by the continuous decrease in the c parameter. The main emphasis in this paper is on slow scan X-ray diffraction (XRD) results, which confirm the existence of a superstructure along the c-direction for the x =0.50 sample. The appearance of some additional peaks, viz. [103], [004], [104] and [112], results in doubling of the lattice parameter along the c-axis. This possibly indicates the alternative ordering of Al and Mg in MgAlB4 separated by hexagonal boron layers but still maintaining the same hexagonal AlB2 type structure. [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: We report the comparisons of the effect on the resistivity behaviors for the four different encapsulated MgB2 samples where we optimized the pure MgB2, using the same standard solid-state synthesis technique, with different shielding materials. The encapsulations were done in Fe Tube, Ta Tube, Ta Foil and Mo Foil, respectively. For the overall comparison, Fe Tube encapsulation seems better sample than others. The lattice parameters ‘a’ and ‘c’ were found to be of the same order. The XRD patterns showed that the compound depicted the single-phase, which are crystallized in the hexagonal structure (space group P 6/mmm) at room temperature, exhibited T c of around 37–39K. We could not completely avoid the inclusion of the foreign particles in our samples, despite having used several encapsulations, but the sample synthesized by this method holds the easiest way to attain better superconducting polycrystalline bulk MgB2. [Copyright &y& Elsevier]

Abstract: We report on the synthesis, phase formation, microstructure, and magnetization, of nano(n)-TiO2-added MgB2 polycrystalline compounds. The added n-TiO2 amounts are varied from 1% to 15% in weight (wt). All the studied samples are near single phase with small amounts of un-reacted Mg/MgO up to 10wt%. The 15wt% n-TiO2 added sample seems to be a multi-phase compound with unusual broadening of the main MgB2 reflection and additional unidentified lines in its X-ray diffraction (XRD) pattern. The superconducting transition temperature (T c), as measured by magnetization experiments, decreases marginally with n-TiO2 addition, for example the T cs are at 37.5K and 35.5K, respectively, for pristine and 10wt% n-TiO2-added samples. This indicates that Ti has not significantly substituted into the host MgB2 lattice. The grain morphology of these compounds reveals porous regions and does not change much with TiO2 addition. High resolution transmission electron microscopy (HRTEM) studies revealed the presence of n-TiO2 in these samples. The critical current density (J c) of the MgB2–n-TiO2 samples, as estimated using the Bean model, shows better performance under magnetic fields above 3T than pristine MgB2 for up to 4wt% of addition, and decreases rapidly for additions above 6wt%. We conclude that n-TiO2 helps in enhancing the flux pinning centers in MgB2 superconductor and hence improves the J c(H) performance for additions up to 4wt% in fields above 3T. [Copyright &y& Elsevier]

Abstract: We report the synthesis and magnetization of Sr2RuREO6 (RE/Ru-211O6) with RE=Gd and Eu. Both Gd and Eu/Ru-211O6 are formed in distorted perovskite-type single phase with monoclinic P21/n space group. Magnetization (M/T) measurements exhibited antiferromagnetic ordering of Ru moments for both Gd and Eu compounds at a T N of around 30K due to super-exchange Ru–O–O–Ru interaction. Interestingly enough, detailed M/H plots of Gd/Ru-211O6 exhibited the development of a ferromagnetic (FM) component at 20K. Furthermore, below 10K, the FM component disappears, and rather spin freezing field (H SF) of around 1000Oe is seen at 5K. In case of Eu/Ru-211O6, the basic antiferromagnetic ordering of Ru moments remains invariantly down to 5K, and the appearance of the FM component is not seen. It seems that the high magnetic moment of 8μ B for Gd3+ influences the anti ferromagnetic (AFM) ordering of Ru in case of Gd/Ru-211O6. [Copyright &y& Elsevier]

Abstract: Raman spectroscopy studies are reported for the RuSr2Eu1.5Ce0.5Cu2O10 (Ru-1222) compound at various temperatures of 300, 250, 200 and 90 K. Three distinct vibrational bands: the first at 110, 140, and 160 cm−1, the second at 295 and 347 cm−1, and third one at 651 cm−1 are seen in Raman spectra of the compound at room temperature. These bands are attached to the Cu atoms’ -direction, the Ru atoms’ ab-plane stretching and Ru atoms’ -direction anti-stretching modes. Below 200 K, an extra vibrational mode is also seen at 260 cm−1. Also, with a decrease in temperature, though the Cu vibrational modes remain intact, the Ru atoms’ ab-plane stretching (295 cm−1) and -direction anti-stretching (651 cm−1) modes shift gradually to higher wave number positions. The frequencies of modes at 260 and 651 cm−1 showed anomalous softening and line-width broadening below 100 K that corroborates well with the spin ordering seen in susceptibility studies. The studied compound is a ferromagnetic superconductor with magnetic ordering of the Ru spins at 200 K and superconductivity below 30 K. A magnetic and electrical transport characterization of the compound is also presented briefly. [Copyright &y& Elsevier]

Abstract: We report synthesis and magnetization of MSr2Y1.5Ce0.5Cu2O10 (M/Y-1222) compounds with M = Ru, Mn and Cr by HPHT. They are synthesized at high-pressure of 6 GPa in optimized temperatures of up to 1450 °C, for Ru, Mn and 1550 °C in the case of Cr based Y/1222, for a time duration of three hours for all the samples. All the samples crystallized with tetragonal structure in I4/mmm space group. Few minor impurities are also seen in the case of Mn,Cr/Y-1222 samples. DC magnetic susceptibility measurements exhibited ferromagnetic like transition for all the three compounds at low temperatures. At 5 K, the magnetization M(H) experiments showed clear ferromagnetic like hysteresis loops for Ru and Mn samples with sizeable returning moment (M r) and coercive field (H c). In the case of Cr/Y-1222 system though, ferromagnetism is visible below around 45 K in susceptibility measurements, the characteristic M r and H c are not seen. To the best of our knowledge the Mn,Cr/Y-1222 phases are synthesized for the first time and the quality of our earlier reported Ru/Y-1222 is improved. [Copyright &y& Elsevier]

Abstract: We report the synthesis, (micro)structure, magneto-transport and magnetization of polycrystalline La2/3Ca1/3MnO3:Ag x composites with , 0.1, 0.2, 0.3 and 0.4. The temperature coefficient of resistance (TCR) near ferromagnetic (FM) transition is increased significantly with the addition of Ag. The FM transition temperature is also increased slightly with Ag addition. Magneto-transport measurements revealed that magneto-resistance MR is found to be maximum near . Further the increased MR of up to 60% is seen above 300 K for higher silver added samples in an applied field of 7 T. Sharp TCR is seen near with the highest value of up to 15% for Ag(0.4) sample, which is an order of magnitude higher than the present pristine sample and the best value yet reported for any polycrystalline LCMO compound. Increased TCR, and significant above room temperature MR of La2/3Ca1/3MnO3:Ag x composites is explained on the basis of improved grain size and connectivity with silver addition in the matrix. Better coupled FM domains and nearly conducting grain boundaries give rise to improved physical properties of the La2/3Ca1/3MnO3 manganites. [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]

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]

Abstract: We report systematic studies of structural, microstructural and transport properties of Y1−x Ca x Ba2Cu3O7−δ bulk samples with 0.20⩾ x ⩾0.0. The partial substitution of Ca2+ at Y3+ site in YBa2Cu3O7−δ leads towards slightly overdoped regime, which along with disorder in CuO2 planes is responsible for decrease in superconducting transition temperature (T c) of the doped system. The microstructural variants being studied by transmission electron microscopy (TEM) technique in imaging and selected area diffraction modes revealed an increase in the density of twins with increase in Ca concentration despite the fact that there is slight decrease in the orthorhombicity. This is against the general conviction of decrease in twin density with decreasing orthorhombicity. An increase in twin density results in sharpening of twin boundaries with increasing Ca concentration. These sharpened twin boundaries may work as effective pinning centers. A possible correlation between microstructural features and superconducting properties has been put forward and discussed in the present investigation. [Copyright &y& Elsevier]

Abstract: Samples of Y0.4Pr0.6Ba2−xSrxCu3O7 (0.0⩽x⩽1.0) have been synthesized by a solid-state reaction route. The samples with x⩽0.60 crystallize in an orthorhombic structure (with orthorhombic distortion decreasing with increasing x), while the samples with x=0.80 and 1.0 crystallize in a pseudo tetragonal structure. Resistance (R) measurements as a function of temperature (T) show that x=0.0 sample is highly semiconducting with R2K/R300K ratio of ∼65. This ratio decreases to only ∼23 and 5 for x=0.20 and x=0.4 samples, respectively. Further, the x=0.60 sample shows onset of a broad superconducting transition temperature at around 20K without achieving the state down to 2K. The state is observed in x=0.80 and 1.00 samples at around 5 and 14K, respectively. Thermoelectric power (S), also exhibits state at around 11K and 16K, respectively for x=0.8 and 1.00 samples. Thermoelectric power at room temperature is positive and decreases with increasing x, indicating enhanced number of mobile holes. These results demonstrate that substitution of Sr at Ba site systematically induces metallicity and eventually superconductivity in Y0.4Pr0.6Ba2−xSrxCu3O7 system. The results are explained on the basis of reduced Pr(4f) orbital hybridization with O(2p) in superconducting Cu–O2 planes, resulting in de-localization of the mobile carriers. The role of decreased Pr/Ba intermixing disorder is also considered. [Copyright &y& Elsevier]

The results of micro-structural and detailed magnetization studies are reported here for our recently published TbSr2Cu2.7Mo0.3O7+δ superconductor with a transition temperature (Tc) at as high as 80K [V.P.S. Awana, A. Gupta, H. Kishan, E. Takayama-Muromachi, T. Watanabe, M. Karppinen, H. Yamauchi, S.K. Malik, W.B. Yelon, V. Ganesan, A.V. Narlikar, Solid State Commun. 129 (2003) 117]. From XRD and EDX the sample was confirmed to be of single-phase and possess the nominal cation stoichiometry. The SEM images showed well-developed grains for this ceramic high-Tc superconductor. Magnetization measurements at various temperatures and fields revealed bulk superconductivity below 80K. Magnetization versus applied field (M vs H) loops at various temperatures below the Tc exhibited clear full penetration field HP. In normal state (>100K) the susceptibility follows the Curie–Weiss behavior with an effective paramagnetic moment of 9.83μB. [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]

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]

We report here the results of thermogravimetric (TG) analysis on the oxygen non-stoichiometry of RuSr2GdCu2O8−δ (Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10−δ (Ru-1222) samples. With TG measurements carried out in O2 and Ar atmospheres it is found that the oxygen content in Ru-1212 remains less affected upon various annealings, while for Ru-1222 the wider-range oxygen-content tuning is possible. When heated in H2/Ar atmosphere the both phases release oxygen upon breaking down to mixtures of metals (Ru and Cu) and simple oxides (CeO2, Gd2O3, and SrO) in two distinct steps around 300 and 450 °C. This reductive decomposition reaction carried out in a thermobalance is utilized in precise oxygen content determination for these phases. It is found that the 100-atm O2-annealed Ru-1212 sample is nearly stoichiometric, while the similarly treated Ru-1222 sample is clearly oxygen deficient. X-ray absorption near-edge structure (XANES) spectroscopy is applied to estimate the valence of Ru in the samples. In spite of the fact that the Ru-1212 phase was shown to possess less oxygen-deficient RuO2−δ layer, the valence of Ru as probed with XANES is found to be lower in Ru-1212 than in Ru-1222. [Copyright &y& Elsevier]

The results of a systematic study on oxygen stoichiometry are reported for the first three members of the novel CoSr2(Y,Ce)sCu2O5+2s±δ or Co-12s2 homologous series, i.e. Co-1212, Co-1222 and Co-1232 phases, with a SrO–CoO1±δ–SrO–CuO2–(Y,Ce)–[O2–(Y,Ce)]s−1–CuO2 layered structure. The oxygen content was precisely determined by two independent chemical techniques: coulometric Cu+/Cu2+ titration and iodometric titration. Furthermore, oxygen stability/tunability was investigated by means of oxygenative and reductive annealings carried out in a thermobalance. It was revealed that all the three phases are rather stoichiometric in oxygen content (δ≈0) and stable against both oxygenative and reductive annealings. The present results provide us with an indication that the nominally oxygen-stoichiometric B–[O2–B]s−1 “fluorite block”, the characteristic structural element for all layered copper oxides of “category-B” [H. Yamauchi, M. Karppinen, Superlatt. Microstructr. 21A (1997) 128], is non-tunable in terms of the oxygen content not only in the Co-12s2 (s>1) phases but also in other category-B phases. [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]

Samples of compositions, RuSr2GdCu2O8−δ (Ru-1212) and RuSr2Gd1.5Ce−0.5Cu2O10−δ (Ru-1222), were synthesised through solid-state reaction routes. The former crystallized in the space group P4/mmm and the latter in I4/mmm. The magnetization vs. temperature curve measured in 5-Oe field showed a clear branching into zero-field-cooled (ZFC) and field-cooled (FC) curves for Ru-1212 and Ru-1222, respectively, around 140 and 100 K with a cusp at 135 and 80 K and a diamagnetic transition around 20 and 30 K only in the ZFC branch. The two down-turn cusps at 135 and 80 K may be attributed to the antiferromagnetic nature of Ru spins. The isothermal magnetization possessed a non-linear contribution due to a ferromagnetic component at low temperatures below 50 K for both samples. The resistance vs. temperature behaviour of the Ru-1212 samples in applied fields of 0, 3 and 7 T confirmed superconductivity, exhibiting a different type of broadening of the superconductivity transition under magnetic fields from that known for conventional high-Tc superconductors. The magnetoresistance (MR) was negative above the Ru magnetic ordering temperature at 135 K. Below the Ru magnetic ordering temperature MR displayed a positive peak at low fields and became negative at higher fields for Ru-1212. For Ru-1222 MR remained negative both above and below the ordering temperature. A maximum of 2% was observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction (ED) pattern from the Ru-1212 sample showed two types of superstructure: one has a weak spot at the centre of the a*–b* rectangle, and the other at the center of the b* edge only. The latter indicates that either Ru/Cu or vacancy ordering of 2b periodicity takes place along the b-direction. Interestingly, Ru-1222 showed only ED patterns with clean a*–b* and a*–c* planes without any superspots. [Copyright &y& Elsevier]

Samples of the composition CoSr2YCu2O7−δ (Co-1212) were synthesized in a single-phase form and studied using neutron diffraction (ND), chemical analyses and magnetization measurements. The structure of Co-1212 is best described in the space group Ima2 that yields good fit to the observed ND data. No cross-migration between Cu and Co is seen for Co-1212. The overall oxygen content, as determined from the refined oxygen occupancies, comes out to be around 7.0. This is close to the values determined from wet-chemical and thermogravimetric analyses. Unlike in Cu-1212, the complete reduction of Co-1212 in 5% H2/95% Ar atmosphere occurs in a single step, revealing that the amount of reversibly removable oxygen is considerably less than that in Cu-1212. Zero-field-cooled and field-cooled magnetizations, measured in an applied field of 100 Oe, show branching at around 30 K, presumably due to the magnetic ordering of Co moments. The present Co-1212 sample is found not to be superconducting down to 5 K. [Copyright &y& Elsevier]

Samples of compositions, RuSr2GdCu2O8−δ (Ru-1212) and RuSr2Gd1.5Ce−0.5Cu2O10−δ (Ru-1222), were synthesised through solid-state reaction routes. The former crystallized in the space group P4/mmm and the latter in I4/mmm. The magnetization vs. temperature curve measured in 5-Oe field showed a clear branching into zero-field-cooled (ZFC) and field-cooled (FC) curves for Ru-1212 and Ru-1222, respectively, around 140 and 100 K with a cusp at 135 and 80 K and a diamagnetic transition around 20 and 30 K only in the ZFC branch. The two down-turn cusps at 135 and 80 K may be attributed to the antiferromagnetic nature of Ru spins. The isothermal magnetization possessed a non-linear contribution due to a ferromagnetic component at low temperatures below 50 K for both samples. The resistance vs. temperature behaviour of the Ru-1212 samples in applied fields of 0, 3 and 7 T confirmed superconductivity, exhibiting a different type of broadening of the superconductivity transition under magnetic fields from that known for conventional high-Tc superconductors. The magnetoresistance (MR) was negative above the Ru magnetic ordering temperature at 135 K. Below the Ru magnetic ordering temperature MR displayed a positive peak at low fields and became negative at higher fields for Ru-1212. For Ru-1222 MR remained negative both above and below the ordering temperature. A maximum of 2% was observed for the negative MR value at the Ru magnetic ordering temperature. An electron diffraction (ED) pattern from the Ru-1212 sample showed two types of superstructure: one has a weak spot at the centre of the a*–b* rectangle, and the other at the center of the b* edge only. The latter indicates that either Ru/Cu or vacancy ordering of 2b periodicity takes place along the b-direction. Interestingly, Ru-1222 showed only ED patterns with clean a*–b* and a*–c* planes without any superspots. [ABSTRACT FROM AUTHOR]

Samples of the composition CoSr2YCu2O7−δ (Co-1212) were synthesized in a single-phase form and studied using neutron diffraction (ND), chemical analyses and magnetization measurements. The structure of Co-1212 is best described in the space group Ima2 that yields good fit to the observed ND data. No cross-migration between Cu and Co is seen for Co-1212. The overall oxygen content, as determined from the refined oxygen occupancies, comes out to be around 7.0. This is close to the values determined from wet-chemical and thermogravimetric analyses. Unlike in Cu-1212, the complete reduction of Co-1212 in 5% H2/95% Ar atmosphere occurs in a single step, revealing that the amount of reversibly removable oxygen is considerably less than that in Cu-1212. Zero-field-cooled and field-cooled magnetizations, measured in an applied field of 100 Oe, show branching at around 30 K, presumably due to the magnetic ordering of Co moments. The present Co-1212 sample is found not to be superconducting down to 5 K. [ABSTRACT FROM AUTHOR]

Pr1−xSrxCoO3−δ exhibits magnetoresistivity (MR) of up to 40% at 5 K with a strong hysteresis/memory effect. Magnetization measurements on Pr0.9Sr0.1CoO2.99 in an applied field of 100 Oe show that, as temperature decreases, the zero field-cooled (ZFC) and field-cooled (FC) magnetization curves branch clearly at 50 K, and a cusp appears in the ZFC branch at Tcusp∼20 K. Magnetization measurements in various fields between 100 and 10,000 Oe show that both the ZFC–FC branching temperature and, Tcusp, decrease with increasing field. The magnetization-field isotherms at 5 and 10 K show hysteresis loops typical of ferromagnets. No appreciable MR is seen in this compound at 50 K, i.e. at a temperature close to ZFC–FC branching temperature. At 20 K, negative MR of above 16% is observed without any hysteresis effect. We believe that the appearance of a ferromagnetic component at 5 K and 10 K (i.e. at temperatures below Tcusp) within the spin glass state of Co spins is responsible for both large MR and the prominent hysteresis/memory effect in MR. [Copyright &y& Elsevier]

Abstract: Phase pure samples of LaOBiS2 and LaO0.5F0.5BiS2 are synthesized by conventional solid state reaction route via vacuum encapsulation technique at 800°C for 12h. Both the samples are crystallized in tetragonal P4/nmm space group with lattice parameters a=4.066(1)Å, c=13.862(4)Å for LaOBiS2; a=4.069(5)Å, c=13.366(2)Å for LaO0.5F0.5BiS2. Bulk superconductivity is confirmed in LaO0.5F0.5BiS2 with superconducting transition temperature (T c ) of 2.7K by DC magnetization and resistivity measurements. The isothermal magnetization (M–H) measurement shows closed loops with clear signatures of flux pinning and irreversible behavior. The magneto-transport ρ(T,H) measurements show resistive broadening and decrease in T c (ρ=0) to the lower temperature with increasing magnetic field. The magnetic phase diagram involving upper critical and irreversibility fields as a function of temperature has been ascertained. The upper critical field H c2(0) is estimated to be ∼19kOe corresponding to a Ginzburg–Landau coherence length of ∼130Å. [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: Temperature dependence of magnetic susceptibility χ(T) of a pure polycrystalline RuSr2(Eu1.5Ce0.5)Cu2O10 compound in the zero-field-cooled (ZFC) and the field-cooled branches deviate below 150K with a sharp upward turn around 100K. At lower temperatures the ZFC branch shows a cusp at T cusp =75K, a superconducting transition temperature at T c =25K. χ(T) becomes negative around 20K. Isothermal ferromagnetic M(H) loops are observed up to 80K. At 5K, the remanent magnetization and the coercive fields (H c) are 0.6Bohr magnetons and 300Oe, respectively. With increasing T, the H c does not decrease monotonically as expected for normal FM domains, but in an anomalous way with a peak around 80K before collapsing above 150K. Electron spin resonance (ESR) measurements show clear ferromagnetic resonances (FMR) at applied fields of 5mT. Interestingly enough the change in FMR intensity also exhibits a peak around 80K, the same as for H c. [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]

The presently prepared FeSr2YCu2Oz (Fe-1212) sample crystallizes in a tetragonal structure (space group P4/mmm). Rietveld structural refinement of the room temperature neutron diffraction data reveal that nearly half of the Fe remains at the Cu(1)-chain site while the other half goes to the Cu(2)-plane site in the nominal Cu(1)Sr2YCu(2)2O7 or Cu-1212 structure. In this compound, Cu is distributed over the chain and plane sites appropriately. Oxygen content of the present Fe-1212 sample, as determined from the oxygen occupancies, is 7.30(2) per formula unit. Existence of Fe at the two different lattice sites is also confirmed from the room temperature 57Fe Mo¨ssbauer spectrum of the compound. [Copyright &y& Elsevier]

Provides information on a study that investigated the magnetization and heat capacity of the perovskite compound, R...Sr...FeO... with R = La and Pr. Experimental details; Results and discussion on the study; Conclusion.

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: Here, effect of single-walled carbon nano-tube (CNT) doping on transition temperature, lattice parameters, critical current density and flux pinning in MgB2 superconductor was studied. The carbon substitution for B was found to enhance critical current density Jc in magnetic fields but depress critical temperature Tc . The depression of Tc is caused by the carbon substitution for B, which is also confirmed by Rietveld analysis of room temperature XRD patterns of doped samples. We achieved enhancement of critical current density (Jc ) and flux pinning by almost an order of magnitude, particularly in higher magnetic fields. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the determination of critical properties of MgB2 along with the impact of carbon substitution on critical parameters. The change in lattice parameters and decrease of transition temperature, Tc confirms the successful substitution by carbon at boron site. The magneto transport measurements up to 140kOe are carried out to determine upper critical field (H c2). The upper critical field values, H c2 are obtained from ρ–T(H) data based upon the criterion of 90% of normal resistivity. The Ginzburg Landau theory (GL equation) is applied to the ρ–T(H) data which accounts for the temperature dependence behavior of Hc 2 in the low temperature high field region along with the determination of Hc (0) value. The Hc (0) value of about 300kOe is obtained for the carbon doped sample while the same is just near to 160kOe for the pure MgB2 sample. [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 synthesized charge ordered La0.5Ca0.5MnO3 manganites by conventional solid-state route, which crystallizes in single-phase form having orthorhombic structure with Pbnm space group. The electrical transport of the compound exhibits highly semi-conducting behaviour from 300K down to 130K and showed an insulator–metal transition (T MI) with a sharp peak in ρ(T). The low temperature resistance below 30K exhibits some upturn in the ρ(T). The charge ordered state (CO) of the Mn3+/Mn4+ ions is not clearly seen as a step in ρ(T), but the same could be seen as a change in the slope of M(T) curve around charge ordered temperature(T CO). Interestingly, when the sample is cycled for the resistance (R) measurements during cooling/heating process hysteresis of 12K is seen near T MI. The magneto-transport of the synthesized compound in 7T field, exhibits nearly 100% magnetoresistance (MR) between T MI and T CO. The fixed temperature (400, 300, 200, 130, 100 and 5K) MR in ±7T field exhibited up and down cusps at all the studied temperatures. The electrical transport, large hysteresis in ρ(T) and MR results can be explained in terms of complex phase separated magnetic structure of this compound around T MI. [Copyright &y& Elsevier]

Abstract: We have synthesized La0.7Ba0.3MnO3 (LBMO):wt%Ag x and La0.7Sr0.3MnO3 (LSMO):wt%Ag x composites with x=0.0, 0.1, 0.2, 0.3 and 0.4 at different sintering temperatures of 1300 and 1400°C by solid-state reaction route. In our previous work [Awana et al. Solid State Commun. 140 (2006) 410] on La2/3Ca1/3MnO3 (LCMO):Ag x (x=0.0, 0.1, 0.2, 0.3, 0.4) composites, we reported about 12% temperature coefficient of resistance (TCR) for Ag0.4 samples near metal–insulator (MI) transition, which was explained on the basis of better grains connectivity. A sharp MI transition results in high TCR. Such high-TCR material can be used as a bolometer or infrared detector at room temperature. In the present work, it is shown that the TCR is improved with Ag addition for both LBMO:wt%Ag x and LSMO:wt%Ag x composites. In addition to improvement in TCR, high MR is also achieved in the vicinity of room temperature. [Copyright &y& Elsevier]

Superconducting order parameter and its symmetry are important parameters towards deciphering the pairing mechanism in newly discovered superconducting systems. We report a study on penetration depth measurement on Nb 2 PdS 5 that has recently been reported with extremely high upper critical field with possible triplet pairing mechanism. Our data show that at low temperatures the change in penetration depth Δ λ is best fitted with BCS s-wave model for single gap with zero-temperature value of the superconducting energy gap Δ 0 = 1.05 meV, corresponding to the ratio 2Δ 0 / k B T c = 3.9 ± 0.18. The superfluid density in the entire temperature range is well described by single gap with gap ratio 2Δ 0 / k B T c = 4.1 ± 0.13 for λ (0) = 225 nm. [ABSTRACT FROM AUTHOR]

We report the impact of silver addition on granularity of NdFeAsO 0.8 F 0.2 superconductor. The ac susceptibility and electrical resistivity under magnetic field are measured to study the improvement in weak links of NdFeAsO 0.8 F 0.2 with addition of Ag x ( x = 0.0–0.3). The Ag free NdFeAsO 0.8 F 0.2 compound shows superconductivity at around 51.8 K. Typical two step superconducting transitions due to the inter- and intra-grain contributions, induced from the combined effect of superconducting grains and the inter-granular weak-coupled medium respectively are clearly seen in susceptibility [ χ ( T )] plots. In comparison to the pure NdFeAsO 0.8 F 0.2 compound, the coupling between the superconducting grains is significantly improved for 20 at% silver doped sample, and the same is deteriorated for higher Ag content i.e., for 30 at%Ag sample. The magneto transport measurements ρ ( T ) H of polycrystalline 20 at% Ag doped NdFeAsO 0.8 F 0.2 exhibited the upper critical filed [ H c2 (0)] of up to 334 T, which is slightly higher than the one observed for pure NdFeAsO 0.8 F 0.2 . The flux flow activation energy ( U 0 / k B ) varies from 7143.38 K to 454.77 K with magnetic field ranging from 0 T to 14 T for 20 at% Ag doped NdFeAsO 0.8 F 0.2 . In this investigation, our results show that limited addition of Ag improves the granular coupling of superconducting grains of NdFeAsO 0.8 F 0.2 compound. [ABSTRACT FROM AUTHOR]

In the present work, the structural, magnetic, magneto-transport and thermoelectric properties of polycrystalline compounds of La 0.8− x Bi x Ca 0.2 MnO 3 (0≤ x ≤0.1) compounds are reported. Structure refinement using Rietveld method confirms that the samples are single phased and crystallize in rhombohedral structure with R-3C space group. Magnetic studies reveal that the pristine sample exhibits T C at 221 K and it shift towards lower temperature with Bi doping. Deviation of the temperature dependent of inverse susceptibility curves from the Curie–Weiss law confirms the existence of Griffiths-like phase. All the samples exhibit metal to insulator transition at temperature T MI , which is found to decrease with increase in Bi doping which is consistent with the magnetic studies. Magneto-resistance MR % data shows that its peak value increases with Bi-doping. The analysis of electrical resistivity data in the metallic region ( T < T MI ) suggests that the electron–electron scattering is predominant in this region whereas the insulating region ( T > T MI ) is well described using Small polaron hopping ( SPH ) and Mott's variable range hopping ( VRH ) models. Analysis of thermoelectric power data in the high temperature region suggests that the SPH mechanism is operative in this regime, while the analysis of low temperature data reveals that the electron–magnon scattering is dominant in the region. [ABSTRACT FROM AUTHOR]

We study the effect of hydrostatic pressure on superconductivity of new BiS 2 based layered REO 0.5 F 0.5 BiS 2 (RE=La, Pr, and Nd) compounds through the measurements of dc electrical resistivity. The REO 0.5 F 0.5 BiS 2 (RE=La, Pr and Nd) compounds synthesized by solid state reaction route via vacuum encapsulation are crystallized in the tetragonal P4/ nmm space group. At ambient pressure the superconducting transition onset temperatures ( T c onset ) are 2.7 K, 3.5 K and 4.5 K, which are enhanced substantially under external hydrostatic pressure to 10.5 K, 7.8 K and 7.5 K for LaO 0.5 F 0.5 BiS 2 , PrO 0.5 F 0.5 BiS 2 and NdO 0.5 F 0.5 BiS 2 respectively at 1.68 GPa. The normal state electrical resistivity decreases with applied pressure for REO 0.5 F 0.5 BiS 2 (RE=La, Pr and Nd). The electrical resistivity under magnetic field and applied pressure has been measured to estimate upper critical field H c2 (0), the values of which are 15.9 Tesla, 8.8 Tesla and 8.2 Tesla for LaO 0.5 F 0.5 BiS 2 , PrO 0.5 F 0.5 BiS 2 and NdO 0.5 F 0.5 BiS 2 compounds. Substantial enhancement of superconductivity under moderate pressures in studied new BiS 2 based superconductors call for the attention of condensed matter physics community. [ABSTRACT FROM AUTHOR]