Electrical and Magnetic behaviour of PrFeAsO0.8F0.2 superconductor

The superconducting and ground state samples of PrFeAsO0.8F0.2 and PrFeAsO have been synthesised via easy and versatile single step solid state reaction route. X-ray & Reitveld refine parameters of the synthesised samples are in good agreement to the earlier reported value of the structure. The ground state of the pristine compound (PrFeAsO) exhibited a metallic like step in resistivity below 150K followed by another step at 12K. The former is associated with the spin density wave (SDW) like ordering of Fe spins and later to the anomalous magnetic ordering for Pr moments. Both the resistivity anomalies are absent in case of superconducting PrFeAsO0.8F0.2 sample. Detailed high field (up to 12Tesla) electrical and magnetization measurements are carried out for superconducting PrFeAsO0.8F0.2 sample. The PrFeAsO0.8F0.2 exhibited superconducting onset (Tconset) at around 47K with Tc({\rho} =0) at 38K. Though the Tconset remains nearly invariant, the Tc({\rho} =0) is decreased with applied field, and the same is around 23K under applied field of 12Tesla. The upper critical field (Hc2) is estimated from the Ginzburg Landau equation (GL) fitting, which is found to be ~ 182Tesla. Critical current density (Jc) being calculated from high field isothermal magnetization (MH) loops with the help of Beans critical state model, is found to be of the order of 103 A/cm2. Summarily, the superconductivity characterization of single step synthesised PrFeAsO0.8F0.2 superconductor is presented.Comment: 15 Pages Text + Fig

Regional characterization of pigeonpea sterility mosaic disease and exploring broad-based resistance

Pigeonpea sterility mosaic disease (SMD) caused by Pigeonpea sterility mosaic virus (PPSMV) is a serious threat to pigeonpea production in the Indian-subcontinent. Recent reports on the possible existence of two different viruses associated with the SMD further complicate the etiology of this difficult to manage viral disease. In this regard, a comprehensive and systematic survey was taken up across several pigeonpea growing areas in southern India to know the disease prevalence and variability in virus isolates. Further, selected pigeonpea elite genotypes were screened in different locations for their broad-based resistance. Results indicate huge variation in SMD incidence among the surveyed states. The highest disease incidence (9.38 percent) was observed in Karnataka, followed by Tamil Nadu state with 8.44 per cent incidence. Andhra Pradesh and Telangana states recorded disease incidences of 4.51 and 2.08 per cent respectively. Samples collected from Patancheru location and tested using viral-specific RNA-3 segment primers were all positive for both the viruses. However, one of the samples collected from Bengaluru location and four samples from Coimbatore location had a positive reaction for PPSMV-2 only. In order to identify broad-based resistance to SMD, 20 pigeonpea genotypes were screened in three different locations (Patancheru, Bengaluru and Coimbatore) in southern-India during rainy seasons of 2017 and 2018. Among them, ICPL- 16078, ICPL-16086 and ICPL-16087 showed resistance reaction ((≤10 % incidence) in all the three locations, whereas, ICPL-16072, ICPL-16077 and ICPL-16083 showed resistance to Patancheru and Coimbatore isolates but highly susceptible (≥40 % incidence) to Bengaluru isolate

Intriguing complex magnetism of Co in RECoAsO (RE=La, Nd and Sm)

We synthesized bulk polycrystalline samples of RECoAsO (RE=La, Nd and Sm) by solid state reaction route in an evacuated sealed quartz tube. All these compounds are crystallized in a tetragonal structure with space group P4/nmm. The Co, in these compounds is in itinerant ferromagnetic state with its paramagnetic moment above 1.5 microB and the same orders ferromagnetically (FM) with small saturation moment of around 0.20 microB below say 80K. This bulk intrinsic magnetism of Co changes dramatically when nonmagnetic La is changed by magnetic Sm and Nd. Although the itinerant ferromagnetism occurs below 80-100K with small saturation moment, typical anti-ferromagnetic (AFM) transitions (TN1, TN2) are observed at 57K and 45K for Sm and at 69K and 14K for Nd. The transition of Co spins from FM to AFM, for magnetic Sm and Nd in RECoAsO is both field and temperature dependent. For applied fields below 100Oe, both TN1 and TN2 are seen, with intermediate fields below 1-2kOe only TN1 and above say 5kOe the AFM transition is not observed. This is evidenced in isothermal magnetization (MH) plots as well. It is clear that Sm/Nd magnetic moments interact with the ordered Co spins in adjacent layer and thus transforms the FM ordering to AFM. All the studied compounds are metallic in nature, and their magneto-transport R(T)H follows the temperature and field dependent FM-AFM transition of ordered Co spins.Comment: 11 pages text + Figs: Queries to - [email protected] (www.freewebs.com/vpsawana

Synthesis and Characterization of Excess Magnesium MgB2 Superconductor under Inert Carbon Environment

The structural, transport and magnetic properties of MgB2 superconductor heavily blended with Mg is studied. The samples are synthesized with a new approach in both, pressed carbon environment and in flowing argon. The excess magnesium used is observed to play dual role: one being the prevention of Mg losses during the synthesis process and hence maintaining the stoichiometry of MgB2 phase, and second being the formation of Mg milieu probably all around the MgB2 grains to give a ductile and dense structure. Excess Mg also improves the grain connectivity by going in to the pores and there by minimizing the insulating junctions.Comment: 21 pages Text + Figs, comments/auggestions ([email protected]) (www.freewebs.com/vpsawana

Structural and Magnetic Properties of Co1-xFexSr2YCu2O7 compounds

Here we study the structural and magnetic properties of the CoFeSr2YCu2O7 compound with x = 0.0 to 1.0. X-ray diffraction patterns and simulated data obtained from Rietveld refinement of the same indicate that the iron ion replacement in CoFeSr2YCu2O7 induces a change in crystal structure. The orthorhombic Ima2 space group structure of Co-1212 changes to tetragonal P4/mmm with increasing Fe ion. The XPS studies reveal that both Co and Fe ions are in mixed states for the former and in case of later.Although none of the studied as synthesized samples in CoFeSr2YCu2O7 are superconducting, the interesting structural changes in terms of their crystallisation space groups and the weak magnetism highlights the rich solid state chemistry of this class of materials.Comment: 20 pages of Text+Figs: comments/suggestions welcome ([email protected]

Delimitation of lymphatic filariasis transmission risk areas: a geo-environmental approach

BACKGROUND: The Global Programme to Eliminate Lymphatic Filariasis (GPELF) depends upon Mass Drug Administration (MDA) to interrupt transmission. Therefore, delimitation of transmission risk areas is an important step, and hence we attempted to define a geo-environmental risk model (GERM) for determining the areas of potential transmission of lymphatic filariasis. METHODS: A range of geo-environmental variables has been selected, and customized on GIS platform to develop GERM for identifying the areas of filariasis transmission in terms of "risk" and "non-risk". The model was validated through a 'ground truth study' following standard procedure using GIS tools for sampling and Immuno-chromotographic Test (ICT) for screening the individuals. RESULTS: A map for filariasis transmission was created and stratified into different spatial entities, "risk' and "non-risk", depending on Filariasis Transmission Risk Index (FTRI). The model estimation corroborated well with the ground (observed) data. CONCLUSION: The geo-environmental risk model developed on GIS platform is useful for spatial delimitation purpose on a macro scale

Superconducting and magneto-transport properties of BiS2 based superconductor PrO1-xFxBiS2 (x=0 to 0.9)

We report superconducting properties of PrO1-xFxBiS2 compounds, synthesized by the vacuum encapsulation technique. The synthesized PrO1-xFxBiS2 (x = 0.1, 0.3, 0.5, 0.7, and 0.9) samples are crystallized in a tetragonal P4/nmm space group. Both transport and DC magnetic susceptibility measurements showed bulk superconductivity below 4 K. The maximum T-c is obtained for x = 0.7 sample. Under applied magnetic field, both T-c(onset) and T-c (rho = 0) decrease to lower temperatures. We estimated highest upper critical field [H-c2(0)] for PrO0.3F0.7BiS2 sample to be above 4 T (Tesla). The thermally activated flux flow activation energy (U-0) is estimated 54.63 meV in 0.05 T field for PrO0.3F0.7BiS2 sample. Hall measurement results showed that electron charge carriers are the dominating ones in these compounds. Thermoelectric effects (Thermal conductivity and Seebeck coefficient) data suggest strong electron-electron correlations in this material

Connectivity and critical current density of in-situ processed MgB2 superconductors: Effect of excess Mg and non-carbon based additives

In a sequel to our previous paper (J. Appl. Phys. 113, 036908 (2013)), where we reported comprehensive analysis of inter-grain connectivity (A(F)), pinning, percolation threshold (P-c), and anisotropy (gamma) in a series of ex-situ processed MgB2, we address the same issues in in-situ processed samples. MgB2 samples with stoichiometric composition, excess Mg (5wt. %) and further 3wt. % addition of various non-carbon based additives like nano-Ag, nano-Ni, and YBCO are synthesised by the in-situ route. Detailed investigations of X-ray diffraction, magnetization (M), and resistivity (rho) as a function of temperature (T) and field (B) in the range 5-300K and 0-8 T are carried out in all the samples. The resistive superconducting onset T-con similar to 38.6 +/- 0.3K and offset (where rho goes to zero) T-c0 similar to 38.1 +/- 0.3K of the samples stay nearly unchanged. The inter-grain connectivity (A(F)) of the samples varies between 11%-20%. All the additives result in a critical current density (J(c)) higher than the stoichiometric MgB2 sample, where the highest values (e.g., J(c)(1 T, 5K) similar to 1.2 x 10(9) A/m(2)) are observed for the sample with 5 wt. % excess Mg. The major findings based on quantitative analysis of rho (T, B) and J(c) (B, T) data in all the samples are: (1) along with previously studied ex-situ samples, the J(c)(A(F)) shows a significant increase at A(F)similar to 7%; (2) the irreversibility lines lie lower than the characteristic T-c0(B) lines in the B-T phase diagram; (3) a universal core pinning (delta l- and/or delta T-c- type) mechanism is revealed in the entire T range 5-30 K; and (4) typical values of P-c similar to 0.57 +/- 0.04 is indicative of weak link networks