We study the effect of nano(n)-SiC addition on the crystal structure, critical temperature (T(c)), critical current density (J(c)) and flux pinning in MgB(2) superconductors. X-ray diffraction patterns show that all the samples have MgB(2) as the main phase with a very small amount of MgO; further, with n-SiC addition the presence of Mg(2)Si is also noted and confirmed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The T(c) value for pure MgB(2) is 18.9 K under 8 T applied field, while it is 20.8 K for the 10 wt% n-SiC doped sample under the same field. This points towards the increment in the upper critical field value with n-SiC addition. The irreversibility field (H(irr)) for the 5% n-SiC added sample reached 11.3, 10 and 5.8 T, compared to 7.5, 6.5, and 4.2 T for the pure MgB(2) at 5, 10 and 20 K, respectively. The critical current density (J(c)) for the 5 wt% n-SiC added sample is increased by a factor of 35 at 10 K and 6.5 T field and by a factor 20 at 20 K and 4.2 T field. These results are understood on the basis of superconducting condensate (sigma band) disorder and ensuing intrinsic pining due to B-site C substitution clubbed with further external pinning due to available n-SiC/Mg(2)Si pins in the composite system.

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We report the synthesis, (micro)structural, magneto-transport and magnetization of polycrystalline La 2/3 Ca 1/3 MnO 3 :Ag x composites with x = 0.0, 0.1, 0.2, 0.3 and 0.4. The temperature coefficient of resistance (TCR) near ferromagnetic (FM) transition is increased significantly with addition of Ag. The FM transition temperature (T FM ) is also increased slightly with Ag addition. Magneto-transport measurements revealed that magneto-resistance MR is found to be maximum near T FM . Further the increased MR of up to 60% is seen above 300 K for higher silver added samples in an applied field of 7 Tesla. Sharp TCR is seen near T FM with highest value of up to 15 % for Ag (0.4) sample, which is an order of magnitude higher than as for present pristine sample and best value yet reported for any polycrystalline LCMO compound. Increased TCR, T FM and significant above room temperature MR of La 2/3 Ca 1/3 MnO 3 :Ag x composites is explained on the basis of improved grains 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 La 2/3 Ca 1/3 MnO 3 manganites. Ag composites Ag is not substituted into main LCMO lattice but remain rather as an additive in the system. (280 K) is comparable to aligned thin films [6,8,15] of LCMO, and to our knowledge is the best one yet obtained for any polycrystalline mangenites. As far fixed temperature and varying field MR is concerned its shape is changed from U type to V type. And is maximum at all fields up to 7 Tesla at 300 K. Infact with an increase in Ag content the low T below 300K MR% decrease and the room temperature 300 K increase. For LCMO: Ag (0.4) sample the MR of up to 60% is observed in 7 Tesla field at 300 K. Even at low fields of say 1 Tesla the MR of up to 16% is seen.The results of magnetization and magneto transport of LCMO:Ag x composites can be summarized as follows: 7 1. Ag does not substitute into host LCMO matrix in our polycrystalline LCMO:Ag x composites but improved significantly the grain morphology of the host.2. The T MI and T c remain nearly invariant with increase in x (Ag content).3. The sharpness of insulator-metal transition increases dramatically with increase in x (Ag content) and high (15%) sharp TCR is observed for Ag composites 4. Though the MR is seen in all the samples right from 300 K down to 5 K, the same is negligible at 300 K and more at lower T for pure sample and is maximum at 300 K and least at 5 K for Ag (0.4) containing compounds. DISCUSSIONNow we try to explain in broad sense the main results summarized above, as far as (1) is concerned there are some very recent reports in literature, which deals with the LCMO and LCMO/ZrO 2 [20]. In all these composites the quality of the LCMO was deteriorated. In case of LCMO:Ag there is a good probability of Ag being distributed at grain boundaries and hence providing better connectivity of grains, which is seen in Fig. 2(b). In most of other composites [16][17][18][19][20] the addi...

We study the effect of synthesis temperature on the phase formation in nano(n)-SiC added bulk MgB 2 superconductor. In particular we study: lattice parameters, amount of carbon (C) substitution, microstructure, critical temperature (T c ), irreversibility field substitution enhances the H c2 while the low temperature synthesis is responsible for the improvement in J c due to the smaller grain size, defects and nano-inclusion induced by C incorporation into MgB 2 matrix, which is corroborated by elaborative HRTEM (highresolution transmission electron microscopy) results. We optimized the the T c (R=0) of above 15K for the studied n-SiC doped and 750 0 C synthesized MgB 2 under 140 KOe field, which is one of the highest values yet obtained for variously processed and nanoparticle added MgB 2 in literature to our knowledge.

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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 FeSe 1/2 Te 1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a = 3.8015͑2͒ and c = 6.0280͑4͒ Å. Magnetization measurements indicated bulk superconductivity with lower critical field ͑H c1 ͒ of around 180 Oe. By applying Ginzburg-Landau theory, the H c2 ͑0͒ value is estimated to be ϳ1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at T c near 13 K and an expected decrease in the same was observed under an applied magnetic field.

a b s t r a c tHere we report the structural, electrical and magnetic properties of Fe doped La 0.7 Ca 0.3 Mn 1−x Fe x O 3 (LCMFO; 0 ≤ x ≤ 1) prepared by conventional solid state reaction method. Simulated data on XRD shows an increase in volume with an increase in Fe ion concentration. XPS supports that Fe 3+ ions directly substitute Mn 3+ ions. Shifting towards lower wave number and symmetric IR band structure confirms increase in volume and homogeneous distribution of Fe ions. Fe ion does not contribute in double-exchange (DE) conduction mechanism due to its stable half filled 3d orbital. The presence of Fe 3+ ions encourages anti-ferromagnetism (AFM) generated by super-exchange interaction and suppress insulator-metal transition temperature (T IM ). Magnetic measurements show the existence of magnetic polarons supported by increase in volume of unit cell and deviation from Curie-Weiss law.

We report an easy single step synthesis route of title compound Although by now nearly two years are over after the discovery of superconductivity in C. Finally the sample was allowed to cool down to room temperature. All the heating schedules were given in one single step. The resultant compound was hard enough for transport measurements and was black in color. Typically, 1 gram of raw pellet was sealed in 2.5 cm diameter and 10 cm length high quality "thick walled" quartz tube. The X-ray diffraction pattern of the compound was taken on a Rigaku diffractometer using CuK α radiation and the Rietveld analysis was carried out to know the lattice parameters and impurities etc., if present at all. Magneto-resistivity measurement R(T)H up to 14 T Field and DC magnetic susceptibility in both zero-field-cooled (zfc) and field-cooled (fc) situations along with the isothermal magnetization (MH) measurements were carried out on a physical property measurement system (PPMS) from Quantum Design (QD). The AC susceptibility at different frequencies (33 to 9999 Hz) & different amplitudes (1 to 15 Oe) of AC drive field with 4 temperatures down to 5 K, the specific heat with temperature down to 2.2 K and thermo-electric power (TEP) were also measured on the same physical property measurement system (PPMS). Figure The upper critical field is determined using different criterion of H c2 =H at which =90% N or 50% N or 10% N , where  N is the normal resistivity or resistance at about 51 K. RESULTS AND DISCUSSIONThe H c2 variation with temperature is shown in Figure 2(c). To determine H c2 (0) value, we applied Ginzburg Landau (GL) theory. The GL equation is:Where, t=T/T c is the reduced temperature [18]. DC magnetic susceptibility versus temperature plot in both zero-field-cooled (zfc) and field-cooled (fc) situations is given in Figure 3. The applied magnetic field is 50 Oe.Superconductivity sets in below 49 K, as evidenced from clear diamagnetic signal at this temperature. Although the transition seems slightly broad the same is still sharper than previous reports on polycrystalline NdFeAsO/F [14,15]. Both zfc and fc are nearly saturated below 30 K.As far as the determination of superconducting volume fraction is concerned the same cannot be ascertained without ambiguity primarily due to positive paramagnetic contribution to magnetic susceptibility from Nd/Fe moments and secondly the pinning defects and impurities hamper the real outcome. Still one can say with confidence that the studied compound is a bulk superconductor with shielding fraction above 25% and superconducting volume fraction of > 8%. 7Measurement of the AC susceptibility can be conveniently used to investigate both intergrain and intragrain vortex dynamics in superconductors [31][32][33]. Figure sample is a granular superconductor like other reported oxy-pnictides.The temperature variation of the AC susceptibility measured at different AC field amplitudes 1, 2, 4, 6, 8, 10, 12, 13 & 15 Oe is shown in Figure 5. The diamagnetic onset temperature is ~ 47.7 K...