Effect of Particle Size on Magnetic Phase Coexistence in Nanocrystalline La0.4Bi0.3Sr0.3MnO3

Journal of Superconductivity and Novel Magnetism - Magnetic phase coexistence in the substituted perovskite compound, La0.4Bi0.3Sr0.3MnO3, is attributed to the spontaneous moment and a step-like...     

Studies on <Emphasis Type="BoldItalic">n</Emphasis>- and <Emphasis Type="BoldItalic">p</Emphasis>-type metal oxide compounds for thermoelectric device fabrication

We report the high-temperature thermoelectric properties of electron- and hole-doped calcium manganese oxide materials, which exhibit potential of a thermoelectric device for conversion of wasteful thermal energy into useful electrical energy. Electron-doped \(\hbox {Ca}_{0.9}\hbox {R}_{0.1}\hbox {MnO}_{3}\) (R = La, Yb) and hole-doped \(\hbox {Ca}_{4}\hbox {Mn}_{2.85}\hbox {Nb}_{0.15}\hbox {O}_{10}\) manganites chosen for the present study were prepared by solid-state reaction of starting compounds and characterized by powder X-ray diffraction. Electrical resistivity and thermopower were measured as a function of temperature to determine the power factor for all the three compounds studied. We discuss these results according to their application potential as a thermoelectric device.     

Size and grain morphology dependent magnetic behaviour of Co-doped ZnO

We have carried out a comparative study of structural, microstructural and magnetic properties of the two sets of Co-doped ZnO samples synthesized using solid state reaction and sol–gel method. Rietveld refinement of the X-ray diffraction data reveals single phase hexagonal wurtzite structure for all the samples, while the tunnelling electron microscopy measurements show the presence of nano-phase in the sol–gel grown Co-doped ZnO samples. It is found that, the microstructure strongly depends on the synthesis method adopted. Samples with higher Co-concentration synthesized by SSR route exhibit antiferromagnetism while SG grown Co-doped ZnO samples exhibit weak ferromagnetic behaviour. Improved magnetic phase in the SG grown samples has been attributed to the grain morphology.     

Low-field Magnetoresistance,Specific Heat and Magnetocaloric Effect in Sr Substituted Pr<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

We investigate the effect of ionic size variation on the electrical and thermodynamic properties in a series of Pr_0.7Ca_0.3−x Sr _x MnO₃ (PCSMO) samples. The increase in Sr content results in an increase of the unit cell volume, as a bigger Sr²⁺ ion replaces the smaller Ca²⁺ ions. Resistivity measurements show that the increase in the Sr content also results in the induction of a metal–insulator transition (T _MI), which increases with increasing Sr content. The activation energy (E _a), calculated from the resistivity data, decreases with increasing Sr content confirming the metallic character. The effect of the magnetic field on resistivity and specific heat has also been studied.     

Modeling Rainwater Storage in Distributed Reservoir Systems in Humid Subtropical and Tropical Savannah Regions

Using a hydrologic model this study estimated rainwater storages in field-scale on-farm reservoir (OFR) systems at two locations: (1) Fort Worth, Texas, US; (2) Kharagpur, West Bengal, India. The water storages were estimated for variable OFR sizes: 1%, 5%, 10%, 15%, and 25% of the farm area. Water losses through seepage and evaporation were estimated using variable saturated hydraulic conductivity conditions: 0.33, 0.64, 1.3, 5 cm/h, which corresponded to the ranges of hydraulic conductivity of loam, sandy loam, loamy sand, and sandy soils, respectively. Results indicated that the water loss through evaporation was dominant at the first location, while seepage was at the second location. Changing the OFR sizes captured 5 to 28% of the total rainfall received in the farm area of the first location and 20–40% at the second location. Finally, a comparative economic analysis was made between a distributed OFR system and a centralized large reservoir that indicated that the distributed OFR system benefits exceeded the benefits of a large reservoir.     

Optimization and Simulation Modelling for Managing the Problems of Water Resources

Waterlogging and secondary salinization have become a serious problem in the canal irrigated areas of arid and semi–arid regions worldwide. In this study, a unique and simple technique was evolved in which a linear programming (LP) optimization model was first developed that allocates available land and water resources in order to maximize net annual returns by mitigating the waterlogging problems. A finite–difference two–dimensional simulation model was then used to evaluate the long–term impacts of various water management strategies on the groundwater table with the optimal land and water use parameters which were obtained through the optimization model. The model was used to combat the waterlogging and salinity problem of an area located in Haryana State of India. The calibration, validation, sensitivity analysis, and error analysis of the model was performed before it was used to study the impact of various water management scenarios on the long-term groundwater level. Based on the model results a change in cropping pattern with reduced rice area is suggested. Groundwater withdrawal should be increased by 1–7 % in the various nodes. It is concluded from the analysis of various scenarios that implementing multiple approaches simultaneously are more effective in controlling waterlogging problems as compared to individual interventions.     

Magnetic Anomalies and Electronic Structure of Ce<Subscript>2</Subscript>Cu<Subscript>2</Subscript>Mg and Ce<Subscript>2</Subscript>Pd<Subscript>2</Subscript>Mg

The intermetallic compounds RE ₂Cu₂Mg and RE ₂Pd₂Mg (RE=La, Ce) were prepared and characterized by magnetic susceptibility and heat-capacity measurements. They crystallize with an ordered U₃Si₂ type structure (space group P4/mbm) and the cerium compounds contain stable trivalent cerium ions, which undergo antiferromagnetic ordering at ∼7.5 and ∼4 K, respectively. In high magnetic fields Ce₂Cu₂Mg exhibits spin reorientation with critical field strength of 40 kOe at 5 K. The data are compared to the non-magnetic isotypic compounds La₂ T ₂Mg (T=Cu, Ni, Pd) and to the already reported intermediate valent Ce₂Ni₂Mg.     

Structural Investigations of La-2125 Mixed Oxide Superconducting System

Crystallographic studies on the (La_{2 – x} Nd _x )Ca _y Ba₂Cu_{4 + y} O _z [y = 2x; 0.0 x 0.5] samples are carried out using neutron diffraction technique. The analysis of the neutron diffraction patterns for the series of samples with 0.0 x 0.5 was done using Rietveld method. The La₂Ba₂Cu₄Oz (La-224, x = 0.0) system exhibits tetragonal phase and is a nonsuperconductor, which on addition of a CaCuO₂ rock salt like layer becomes superconducting. It is important to note the significant role played by Ca-doping in improvising the superconducting properties. Analysis of the structural data reveals that, as Ca concentration increases, the unit cell volume decreases while T _c increases with a maximum value of 78 K for y = 1.0. The detailed crystal structure for LaNdCaBCO series of samples has been studied in the light of changes in bond lengths with increase in Ca concentration and its role in turning on the superconductivity.