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Polycrystalline samples of Ni1 − xCoxFe2O4 (where x = 0.0, 0.4, 0.5, 0.6, 1.0) have been synthesized by solid state sintering of stoichiometric nanoparticles prepared by sol–gel technique. Rietveld refined powder X-ray diffraction patterns confirm the formation of a single cubic spinel phase in each sample. Substitution of cobalt ions results in the increase of the lattice parameter. The saturation magnetization and coercivity of all the samples were measured using PPMS-VSM and found to increase from 51.6 to 82.2 emu/g, and 9.7 to 588 Oe, respectively. The observed magnetic ordering is explained on the bases of two sublattice model and redistribution of cations in these partially inverse Co substituted Ni ferrite samples. The strong increment (60 times) in the coercivity is explained on the bases of microstructure and magnetocrystalline anisotropy. Cation redistribution in these samples is proposed on the basis of the observed magnetic moment. Close matching of lattice parameter calculated from the magnetic data and estimated from the X-ray diffraction data supports the proposed cation redistribution in the partially inverse spinel phase of NCFO.

Functionally graded tungsten–copper bimetallic compact with fine microstructure and good mechanical property has been synthesized by employing microwave heating method at a temperature of 800 °C and in a short processing time of 30 min. Scanning electron microscopy and energy dispersive X-ray analysis revealed the graded structure of synthesized sample. The fine microstructure of tungsten in each layer is caused by arrested grain growth because of the short sintering time. The overall relative density of the W/Cu functionally graded sample has reached 87% of the theoretical density. Vickers microhardness measurements, across the length of a compact, show increase in hardness value of the sample with the increase in tungsten content. The experimental hardness values match well with the theoretically calculated hardness values.

Single-phase nanoparticles of Mn0.5Zn0.5Fe2 O 4 (MZF) with improved magnetic properties were prepared from the precursor (formed by chemical route) by microwave processing technique at 500 ∘C in only 3 min. Crystallographically, these were found to be of spinel phase. Using Debye-Scherrer formula, the particle size of conventionally sintered powder is estimated to be about 20 nm, whereas that of microwave processed is nearly 50 nm with improved grain size. The field emission scanning electron (FESEM) and transmission electron (TEM) micrographs revealed the particles in microwave-processed samples to be spherical in shape and confirmed the sample size (to be nearly 50 nm). Room temperature magnetization measurement of conventionally sintered samples (by vibrating sample magnetometer (VSM)) showed their superparamagnetic nature with saturation magnetization of nearly 19 emu/g. The microwave-processed samples showed improved saturation magnetization of nearly 36 emu/g, which is even better than the reported value.

Observation of room temperature ferromagnetism (RTFM) is reported in polycrystalline thin films of Ti1−xMnxO2 (x = 0.10 and 0.15) synthesized by spray pyrolysis technique on fused quartz substrates. Our experimental results clearly suggest partial incorporation of manganese (Mn) in titanium dioxide (TiO2) lattice up to certain extent and rest of the Mn ions are consumed to form secondary Mn-related phase such as manganese oxide (Mn3O4). The observed weak ferromagnetic ordering at room temperature in the films is established to be due to incorporation of Mn in TiO2matrix rather than the presence of other secondary phases since none of the Mn or Ti/Mn oxide phase is ferromagnetic at room temperature. Bound magnetic polaron model is invoked to explain the observed ferromagnetism in these highly resistive films.

The present paper describes our results on the phase transformation (from crystalline to amorphous) of M-type hard barium hexaferrite, and consequently its conversion into soft ferrite by the application of magnetic energy at microwave frequency (2.45 GHz). The rapid volumetric heating of the conventionally prepared polycrystalline hexaferrite by microwave energy at a temperature of 950 °C in a short duration of only 5 min resulted in a decrystallized phase. The magnetic studies (M–H loops) of the resistively heated and MW processed samples have revealed a lowering in coercivity (from 188 to 2 mT) in the latter samples, thereby establishing the formation of soft ferrite. An attempt has also been made to understand the observed transformation from hard to soft ferrite.

Nanocrystalline samples of both undoped TiO2 and with 5 at.% Co at cationic sites were prepared by a simple chemical route. X-ray diffraction study of these samples revealed an increase in lattice parameters due to incorporation of Co in the TiO2 lattice and possibly due to formation of oxygen vacancies. No traces of crystalline Co or any other secondary phases could be detected. High-temperature SQUID measurement of these samples exhibited ferromagnetic signature up to 700 K, implying that the Curie temperature of doped and undoped TiO2 exceeds 700 K. Vacuum annealing of both types of samples enhanced the ferromagnetic character. The as-prepared and vacuum-annealed Co incorporated TiO2 samples, in addition to the ferromagnetic character, also exhibited a paramagnetic signal. All these measurements strongly support the role of defects in inducing room-temperature ferromagnetism in undoped and Co doped TiO2 nanopowders, which can be explained using the bound magnetic polaron model.

Thin films and nanowires of Fe3O4 have potentiostatically been electrodeposited on ITO coated glass and employing templates in a conventional three-electrode cell using two different baths. Appropriate potential windows, suitable for films and nanowires, were estimated from cyclic voltametry. Structural property of Fe3O4 films was studied by X-ray diffraction. A large (−3.35%, at 2.3 kOe) longitudinal magnetoresistance (MR) was observed at room temperature, and the shape of MR curves showed a reduced hysteresis loop for Fe3O4 films with low coercivity. Room-temperature magnetic properties of Fe3O4 films were studied by vibrating sample magnetometer (VSM). Surface morphology of nanowires was studied by scanning electron microscope (SEM). The nonlinear I–V characteristic of nanowires was observed at room temperature. An attempt has been made to understand the conduction mechanism.

NiCuZn ferrite has recently attracted a lot of attention for its application in high frequency (up to a few GHz) multilayer chip inductors (MLCIs) and for other microwave devices owing to their favorable electromagnetic properties and low densification temperature. In order to study the effect of substitution of cations by cobalt in small concentration on the dielectric and magnetic properties at low and high frequencies, bulk polycrystalline ferrite samples of starting composition (Ni0.2Cu0.2Zn0.6)1 − x Co x Fe2O4, having x = 0, 0.01, 0.03 and 0.05, were prepared by citrate precursor method. Pure spinel (cubic) ferrite formation was confirmed by powder X-ray diffraction technique. Complex permittivity and permeability were measured at microwave frequencies (X-band) using the cavity perturbation method, which is a non-contact method. The values of real part of permittivity (e ′) vary in the range 7–9.6 and of the imaginary part (e ″) vary from 0.020–0.120, whereas real part of the permeability (μ′) lies in the range 2.6–14.0 and the imaginary part of permeability (μ″) varies from 0.5–6.0. It is observed that there is an increase in μ′ and decrease in the magnetic loss (tan δ μ) on increasing the cobalt concentration from x = 0 to x = 0.05. The variation of these parameters, both with frequency in X-band and with the cobalt concentration, is discussed in this paper.

Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1:2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (T C) and critical current density (J C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2:2 ratio, at temperatures around 790°C. Critical current density has been found to vary systematically with processing temperature.

Genetic Variability, Character Association and Path Analysis Studies for Grain Yield and Contributing Traits in Rice (Oryza Sativa L.) under Temperate Conditions of Kashmir A comprehensive study was done for the assessment of genetic variability, character association and path-coefficient using fourteen agro-morphological traits among 35 rice (Oryza sativa L.) genotypes under temperate conditions of Kashmir valley. Analysis of variance (ANOVA) revealed a substantial level of variability among the tested genotypes for all the traits. The greater values of phenotypic coefficient of variation (PCV) over genotypic coefficient of variation (GCV) for all the characters unveiled the influence of environment on character expression. Harvest index showed the highest values of GCV (33.26) and PCV (33.59) and lowest for 1000 grain weight (6.66) and (7.08). High heritability together with high genetic advance was observed in biological yield (0.99) and (53.01). Number of spikelets per panicle (0.49). (46.50), denotes the number of filled grains per panicle (0.99) and (41.90). However, high heritability associated with low genetic advance as percentage of mean was observed for days to maturity (97.00) and (15.11) and 1000 seed weight (89.00) and (12.90). Correlation studies revealed that harvest index (0.47) and (0.43) showed significant positive correlation with grain yield per hill at both genotypic and phenotypic level. While as days to 50% flowering (-0.31) and (-0.28) showed significant negative correlation with grain yield per hill. Path coefficient studies revealed that at genotypic level flag leaf length (0.62) showed high direct positive effect with grain yield per hill followed by flag leaf width (0.61) - while as at phenotypic level flag leaf area (0.49) showed maximum positive direct effect with grain yield per hill followed by harvest index (0.36).)....

In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium substituted (partially) large single crystals of high temperature superconducting Y1−x Pr x Ba2Cu3O7−δ (x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm3 and 4 × 1 × 1 mm3, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y0·8Pr0·2Ba2Cu3O7−δ and Y0·6Pr0·4Ba2Cu3O7−δ materials are ≈ 2 × 3 × 0·1 mm3 and 5 × 1 × 1 mm3 and ≈ 1 × 1·5 × 0·1 mm3 and 7 × 0·2 × 0·1 mm3, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T c) of the oxygenated crystals were found to depend on the Pr-content.

Bismuth germanium oxide (BGO) has tremendous application potential due to its favourable electro-mechanical and electro-optic properties. The present paper describes some of our preliminary results on the variation of dielectric constant with applied high hydrostatic pressure and temperature. It is noted that BGO is a promising candidate for its application as a pressure sensor.

Small additions of MnO2 up to 15 at. % in YBa2Cu3O7−δ in place of Cu have been carried out to study their influence on the superconducting properties. It has been found that transition temperature and microstructure of Mn-doped samples are highly sensitive to the sintering temperature and Mn content. The normal state resistance increases with Mn content. Microstructure shows plate-like grain growth for low Mn contents (up to x = 0.05) at higher sintering temperature. XRD and microstructure reveals the presence of additional Y2BaCuO5 and Ba3Mn2O8 phases with an increase in Mn content. Also, reduction in the diamagnetic signal and broadening of transition is observed beyond certain Mn content. A detailed discussion of microstructure, XRD, normalized resistance, and magnetic properties has been carried out in correlation with sintering temperature and Mn content.

DC magnetization measurements have been carried out on bulk YBCO/Ag composites with silver content up to 20wt per cent. DC fields in the range 0·5 mT to 200 mT have been used to investigate the inter- and intragranular properties at 77K. The AC susceptibility as a function of temperature at different AC fields (0·026–0·30 mT) has also been studied. Under small DC fields (≈ 4 mT), depending on the Ag content andH max, the M-H loop shows a complicated behaviour. This behaviour can be explained on the basis of effect of strong field dependence of transport critical current, grain size and intragrain critical current densityJ cgm on low-field M-H loop. The estimation of intergranular critical current densityJ cjm from these loops does not remain a simple function of ΔM/d. The AC susceptibility measurements show a small increase inJ c(T) with silver content under low AC fields only, consistent with the transportJ c data; beyond thatJ c(T) decreases. This improvement inJ c(T) and transportJ c with silver can be ascribed to the improved coupling between grains but not to the pinning. Also at higher field (H max>20 mT) the addition of Ag decreases the intragrain critical current density. The upper critical field of intergranular regionH c2j and lower critical field of intragrain regionH c1g also decrease with silver content.

The role of cationic ratios (Sr/Ca and Bi/Pb) in the evolution of high-T c phase (2223) in samples prepared under different sintering conditions, starting with a composition of Bi2Pb0.6Sr2Ca2Cu3.1Oy, has been investigated by employing energy-dispersive X-ray analysis, scanning electron microscopy and X-ray diffraction. As manifested by the observed decrease in Sr/Ca ratio, an increase in sintering temperature from 822 to 852 °C increases the disorder in Sr-O and Ca layers. The observed increase in the volume fraction of 2223 phase and the contraction inc-axis parameter have been explained on the basis of the observed decrease in Sr/Ca ratio. It thus appears that the disorder caused by the intersubstitution of Ca and Sr in SrO and Ca layers and partial replacement of Bi by Pb in the structure promote the evolution and growth of 2223 phase.

The role of preparation conditions and the effect of addition of Pb in Bi-Sr-Ca-Cu-O (BSCCO) superconductor, on theTc,Jc and grain orientation have been studied. Calcination at a temperature higher than the melting point of Bi2O3 after the prereaction at 800°C leads to formation ofc-axis oriented nearly single phase material. The presence of lead yields a nearly highTc phase (2223) exhibiting a maximum transition temperatureTc=110 K and ΔTc=2 K. The addition of lead and grain orientation together result in an increase inJc by nearly two orders of magnitude. The degradation behaviour was studied in terms of changes inTc,Jc and structure on exposure to atmosphere up to 250 days. Samples with 0.6 Pb were found to be superconducting withTc=97 K even after 250 days. The highTc phase was stable against degradation. Our studies indicate that the degradation of leaded BSCCO is a surface phenomenon rather than bulk phenomenon.

Studies on Mn, Ni and Co doped ZnO systems have revealed that the RTFM present in these systems can be both intrinsic and extrinsic depending on the choice of TM ion incorporated, technique of preparation and post-synthesis processing. Choice of such a technique that ensures better homogeneity and incorporation of TM ions in the ZnO host, leads to the occurrence of intrinsic, stable and robust RTFM. The air ambient processing eliminates the chances of any metallic cluster inclusions, and instead such TM oxide phases are formed that are non-ferromagnetic. However, post synthesis processing like vacuum annealing of ZnO:Co samples under some situations can give rise to occurrence of extrinsic RTFM. But, this can be overcome by certain additional processing step. ZnO:Co samples with intrinsic RTFM, stable upto 900°C annealing with Curie temperatures in excess of 450°C have successfully been prepared.

Intrinsic room temperature ferromagnetism is reported in sequentially sintered (in air ambient) nanocrystalline ZnO:Co (1 to 10 at% Co) samples prepared by chemical route. The Curie temperature of the ZnO:Co ferromagnetic samples is determined to be ∼495°C. The saturation magnetization of the ferromagnetic phase is found to first increase with Co concentration (up to 5%) and then decrease. It is also found to decrease with increase in sintering temperature up to 800°C; there after it remains unaffected till 1000°C. The d-d band transitions in the optical spectrum confirm that Co2+ substitutes Zn2+ in the ZnO lattice. A plausible explanation of the observed ferromagnetic ordering is presented in terms of Bound Magnetic Polarons model.

Electrodeposition has emerged as a novel economically viable technique with large-scale production capabilities in modern day micro technologies. The current trends are to extend the potential of the electrodeposition to nano fabrication. We have successfully electrodeposited Cu/Co multilayers, exhibiting appreciably high GMR, on ITO as well as on Cu/Si substrates. Multilayer stacks with films in thickness range 1 – 10 nm were deposited. The Co layers have different mechanisms of growth on these substrates, thus resulting in different microstructure and topography of the electrodeposited films. This leads to different GMR behavior of the multilayers in both these cases. Room temperature GMR values of 15% at low fields are obtained on ITO substrate and higher values are possible on Cu/Si substrate.

The effect of composition, sintering parameters, frequency and temperature on the dielectric parameters of ZnO-based ceramic semiconductors (cersems) having small amounts of Bi2O3, Sb2O3, CoO, MnO2, La2O3 and/or Cr2O3 has been investigated. The unusually high dielectric constant of these composites, arising due to a two-phase microstructure has been explained on the basis of a depletion layer model. The agreement in values of barrier height and donor concentration calculated fromC −2 −V plot, Hall measurement and I-V characteristics of these cersems supports the validity of barrier and depletion layer models. The depletion and inter-granular layers are estimated to be nearly 102 nm and 1–2 nm respectively. The observed variation of dielectric constant/capacitance with sintering parameters and temperature of measurement has also been explained on the basis of simplified microstructure and depletion layers. The loss peak (f max) observed at 300 kHz remains practically unaltered with change in composition and sintering parameters. The observed dielectric dispersion in the range 102−106 Hz, exhibiting multiple relaxation times and activation energy of relaxation process as 0·36 eV, has been explained on the basis of Debye-type relaxation process originating due to trapping/detrapping and possibly due to scattering of carriers in the depletion regions.