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This study investigates the unsteady, two-dimensional flow and heat transfer past a rotationally oscillating circular cylinder in linear shear flow. A higher order compact (HOC) finite difference scheme is used to solve the governing Navier–Stokes equations coupled with the energy equation on a nonuniform grid in polar coordinates. The hydrodynamic and thermal features of the flow are mainly influenced by the shear rate (K), Reynolds number (Re), Prandtl number (Pr), and the cylinder oscillation parameters, i.e., oscillation amplitude (αm), the frequency ratio (fr). The simulations are performed for Re=100,Pr=0.5−1.0, 0.0≤K≤0.15, and 0.5≤αm≤2.0. The numerical scheme is validated with the existing literature studies. Partial and full vortex suppression is observed for certain values of shear parameter K. The connection between heat transfer and vortex shedding phenomenon is examined where a pronounced increase in the heat transfer is observed for certain values of oscillation parameter, relative to the nonshear flow case.

In energy dispersive X-ray fluorescence (EDXRF) analytical studies of samples, the absorption and enhancement of analyte X-rays, collectively called matrix effects, complicate the relation between intensity of analyte X-rays and its concentration. Earlier, the absorption and enhancement relative terms have been derived from the builtup experimental relations of analyte X-ray counts with XRF fundamental parameters and the parameters of the experimental setup for each selective and enhanced X-rays. Now, the terms are implemented on the determined amounts of potassium and calcium nutrients in plants and pot soils from an experiment performed in the lab by growing fenugreek plants on the soils with variable contamination levels and applied fertilizers. The variation pattern of the terms with respective nutrient contents is found to be affected by the basic nature of soils. The pattern shows the high sensitivity of the terms to the plant's behaviour in soil and reflects the picture of supressed benefits of applied fertilizers to the heavy-metals contaminated soils.

The oral route is the most common choice for drug administration because of convenience, low cost, and high patient compliance, but is also a complex route. The rate of dissolution and gastric emptying of the dissolved active pharmaceutical ingredient (API) into the duodenum is modulated by factors such as gastric motility, but current in-vitro procedures for assessing drug dissolution are limited in their ability to recapitulate this process. This is particularly relevant for disease conditions, such as gastroparesis, that alter the anatomy and/or physiology of the stomach. In this study we employ a biomimetic in-silico simulator based on the realistic anatomy and morphology of the stomach, to investigate the effect of body posture and stomach motility on drug bioavailability. The simulations show that changes in posture can have a significant (up to 83%) effect on the emptying rate of the API into the duodenum. Similarly, reduction in antral contractility associated with gastroparesis can also significantly reduce the dissolution of the pill as well as emptying of the API into the duodenum. The simulations show that for an equivalent motility index, reduction in gastric emptying due to neuropathic gastroparesis is larger by a factor of about five compared to myopathic gastroparesis., Comment: 32 pages, 8 figures, supplemental material

Forced convection from a heated rotationally oscillating circular cylinder placed in a uniform cross flow of constant properties fluid is investigated. The two-dimensional governing equations of flow motion and energy are solved numerically on non-uniform polar grids using a higher order compact (HOC) formulation. The flow and thermal fields are mainly influenced by Reynolds number, Re, Prandtl number, Pr, maximum angular velocity of the cylinder, α m , and the frequency ratio, f / f 0 , which represents the ratio between the oscillation frequency, f, and the natural vortex shedding frequency, f 0 . The numerical simulations are performed at Re = 200 , Pr = 0.5 - 1.0 , α m ∈ [ 0.5 , 4.0 ] and f / f 0 ∈ [ 0.5 , 3.0 ] . The resulting lock-on phenomena behind the cylinder is detected and thermal field is determined. Comparisons with previous numerical and experimental results verify the accuracy and the reliability of the present study. Variations in heat transfer coefficients within the lock-on ranges are investigated to build a connection between the heat transfer and the lock-on regimes.

Elemental evaluations in scanty powdered material have been made using energy dispersive X-ray fluorescence (EDXRF) measurements, for which formulations along with specific procedure for sample target preparation have been developed. Fractional amount evaluation involves an itinerary of steps; (i) collection of elemental characteristic X-ray counts in EDXRF spectra recorded with different weights of material, (ii) search for linearity between X-ray counts and material weights, (iii) calculation of elemental fractions from the linear fit, and (iv) again linear fitting of calculated fractions with sample weights and its extrapolation to zero weight. Thus, elemental fractions at zero weight are free from material self absorption effects for incident and emitted photons. The analytical procedure after its verification with known synthetic samples of macro-nutrients, potassium and calcium, was used for wheat plant/ soil samples obtained from a pot experiment.

Metal Chalcogenides have been known for important technological applications and have attracted continuous interest in their structure, electronic, thermal and transport properties. Here we present first principles calculations of the vibrational and thermodynamic properties of NiX (X = S, Se, Te) compounds along with inelastic neutron scattering measurements of the phonon spectrum in NiSe. The measured phonon spectrum is in very good agreement with the computed result. We also report the measurement of thermal expansion behavior of NiSe using X-ray diffraction from 13 K to 300 K. The change in the hexagonal c lattice parameter in NiSe is considerably greater as compared to a parameter. The ab-initio calculated anisotropic Gr\"uneisen parameters of the different phonon modes in all the chalcogenides along with the elastic constants are used to compute anisotropic thermal expansion behviour, which is found in good agreement with experiments. The displacement pattern of phonons indicate that difference in amplitudes of Ni and X atoms follow the anisotropy of thermal expansion behavior along c- and a-axis., Comment: 21 Pages, 9 Figures

In order to identify and quantitatively analyze the anharmonicity of phonons relevant to the anomalous thermal expansion in the Ih phase of ice, we performed neutron inelastic scattering measurements of the phonon spectrum as a function of pressure up to 1 kbar at 225 K in deuterated ice (D2O), and as a function of temperature over 10-225 K at ambient pressure in both H2O and D2O ice. We also performed density functional theory calculations of the lattice dynamics. The anomalous expansion is quantitatively reproduced from the analysis of the neutron data as well as from the ab-initio calculations. Further, the ab-initio calculations are used to visualize the nature of anharmonic phonons across a large part of the Brillouin zone. We find that the negative thermal expansion below 60 K in the hexagonal plane is due to anharmonic librational motion of the hexagonal rings of the ice molecules, and that along the hexagonal axis originates from the transverse vibrations of the hexagonal layers.

The thermal expansion behavior of metal fluorides can be tuned by choosing an appropriate metal cation. We present ab initio lattice dynamical studies on the metal fluorides $(\mathrm{CaZr}{\mathrm{F}}_{6},\mathrm{MgZr}{\mathrm{F}}_{6}$, and $\mathrm{SrZr}{\mathrm{F}}_{6})$ and identify the anharmonic phonon modes responsible for the negative thermal expansion (NTE) in these materials. These phonon modes involve $\mathrm{Zr}{\mathrm{F}}_{6}$ polyhedral rotational motion, which leads to large transverse amplitude of the vibrations of the fluorine atom in the Zr-F-M bond in these compounds. The compounds with larger anisotropy in the thermal amplitude of the fluorine atom show larger NTE behavior. This has enabled us to understand the substantial variation in thermal expansion behavior of these compounds at high temperature. We have also calculated the potential energy profile of selected phonon modes, which enables us to derive the cubic and quartic anharmonic coefficients.

Here, we report inelastic neutron scattering measurements over 7–1251 K in CaMnO3 covering various phase transitions, and over 6–150 K in PrMnO3 covering the magnetic transition. The excitations around 20 meV in CaMnO3 and at 17 meV in PrMnO3 at low temperatures are found to be associated with magnetic origin. We observe coherent magnetic neutron scattering in localized regions in reciprocal space and show it to arise from long-range correlated magnetic spin-waves below the magnetic transition temperature (TN) and short-range stochastic spin-spin fluctuations above TN. In spite of the similarity of the structure of the two compounds, the neutron inelastic spectrum of PrMnO3 exhibits broad features at 150 K unlike well-defined peaks in the spectrum of CaMnO3. This might result from the difference in the nature of interactions in the two compounds (magnetic and Jahn-Teller distortion). Ab initio phonon calculations have been used to interpret the observed phonon spectra. The ab initio calculations at high pressures show that the variations of Mn-O distances are isotropic for CaMnO3 and highly anisotropic for PrMnO3. The calculation in PrMnO3 shows the suppression of Jahn-Teller distortion and simultaneous insulator-to-metal transition. It appears that this transition may not be associated with the occurrence of themore » tetragonal phase above 20 GPa as reported in the literature, since the tetragonal phase is found to be dynamically unstable, although it is found to be energetically favored over the orthorhombic phase above 20 GPa. CaMnO3 does not show any phase transition up to 60 GPa.« less

The physical and structural properties of Fe1.11Te and Fe1.11Te0.5Se0.5 have been investigated by means of X-ray and neutron diffraction as well as physical property measurements. For the Fe1.11Te compound, the structure distortion from a tetragonal to monoclinic phase takes place at 64 K accompanied with the onset of antiferromagnetic order upon cooling. The magnetic structure of the monoclinic phase was confirmed to be of antiferromagnetic configuration with a propagation vector k = (1/2, 0, 1/2) based on Rietveld refinement of neutron powder diffraction data. The structural/magnetic transitions are also clearly visible in magnetic, electronic and thermodynamic measurements. For superconducting Fe1.11Te0.5Se0.5 compound, the superconducting transition with T c = 13.4 K is observed in the resistivity and ac susceptibility measurements. The upper critical field H c2 is obtained by measuring the resistivity under different magnetic fields. The Kim’s critical state model is adopted to analyze the temperature dependence of the ac susceptibility and the intergranular critical current density is calculated as a function of both field amplitude and temperature. Neutron diffraction results show that Fe1.11Te0.5Se0.5 crystalizes in tetragonal structure at 300 K as in the parent compound Fe1.11Te and no structural distortion is detected upon cooling to 2 K. However an anisotropic thermal expansion anomaly is observed around 100 K.

Diffuse polarized neutron scattering studies have been carried out on single crystals of pyrochlore spin ice Ho(2-x)Y(x)Ti(2)O(7)(x = 0, 0.3, and 1) to investigate the effects of doping and anisotropy on spin correlations in the system. The crystals were aligned with the (1 - 10) orientation coincident with the direction of neutron polarization. For all the samples studied the spin flip (SF) diffuse scattering (i.e. the in-plane component) reveals that the spin correlations can be described using a nearest-neighbour spin ice model (NNSM) at higher temperatures (T = 3.6 K) and a dipolar spin ice model (DSM) as the temperature is reduced (T = 30 mK). In the non-spin flip (NSF) channel (i.e. the out-of-plane component), the signature of strong antiferromagnetic correlations is observed for all the samples at the same temperature as the dipolar spin ice behaviour appears in the SF channel. Our studies show that the non-magnetic dopant Y does not significantly alter SF or NSF scattering for the spin ice state, even when Y doping is as high as 50%. In this paper, we focus on the experimental results of the highly doped spin ice HoYTi(2)O(7) and compare our results with pure spin ice Ho(2)Ti(2)O(7). The crossover from a dipolar to a nearest-neighbour spin ice behaviour and the doping insensitivity in spin ices are briefly discussed.

Some selected applications of spin-polarized density functional theory are presented to illustrate the robustness of the applied approaches to help interpretation and to ellucidate some observed, intriguing magnetic behavior, as highlighted by recent neutron scattering experiments. Both structure and dynamics are concerned through four examples covering the elastic and inelastic neutron scattering processes and dealing with the case studies of some complex transition metal containing inorganic materials. In the first two examples, molecular cluster calculations of the magnetic exchange coupling constant and the evaluation of the spin density distribution are shown. Further, periodic simulations of the magnetic bands and the spin-orbit coupling are introduced. Finally, the role of the magnetic interactions in the inelastic case is illustrated through investigating the corresponding effect on phonon dynamics relevant to superconductivity.

The initial development of the two dimensional viscous, incompressible flow induced by an impulsively started circular cylinder which performs time dependent sinusoidal rotational oscillations about its axis is investigated numerically. The investigation is based on the solutions of stream function-vorticity formulation of Navier-Stokes equations on non-uniform polar grids using higher order compact formulation. The numerical method is validated by comparing the computed results with existing experimental and numerical results for Reynolds numbers Re = 150 and 500. The effects of forced oscillation frequency f and peak rotation rate αm on the early development of the flow structure in the near wake region are discussed. Results are given for the initial development with time of the flow structure at the rear of the cylinder at Re = 200. The details of the formation, movement, closure points, and strengths of the vortices behind the cylinder are presented. The velocity profiles at different locations and vorticity profiles at the surface of the cylinder are also shown. The effect of increase in αm on the timing of the formation of the vortices, the closed wake length, and the thickness of the boundary layer is investigated.

The ferroelectric materials are mainly focused on pure inorganic oxides; however, the organic molecule based materials have recently attracted great attention because of their multifunctional properties. The mixing of oxalate and phenanthroline ligands with metal ions (Fe or Mn) at room temperature followed by hydrothermal treatment results in the formation of one–dimensional single chain molecular magnets which exhibit room temperature dielectric and ferroelectric behavior. The compounds are chiral in nature, and exhibit a ferroelectric behavior, attributed to the polar point group C2, in which they crystallized. The compounds are also associated with a dielectric loss and thus a relaxation process. The observed electric dipole moment, essential for a ferroelectricity, has been understood quantitatively in terms of lattice distortions at two different lattice sites within the crystal structure. The studied single chain molecular magnetic materials with room temperature ferroelectric and dielectric proper...

This paper reports detailed lattice dynamical studies involving experimental inelastic neutron-scattering measurements and theoretical shell model calculations of the vibrational and thermodynamic properties of the garnet mineral almandine Fe{sub 3}Al{sub 2}Si{sub 3}O{sub 12}. Inelastic neutron-scattering studies using the time-of-flight technique provide the measurement of the phonon density of states (DOS) of almandine, which have been interpreted based on the model calculations. The calculated DOS is in good agreement with the inelastic neutron-scattering data and has been used to compute various macroscopic properties like the specific heat, thermal expansion, equation of state, and mean-square atomic displacements. (c) 2000 The American Physical Society.

We have measured phonon spectra of Ag3M(CN)6 (M=Co,Fe) using neutron time-of-flight spectroscopy as a function of temperature and pressure. Ab-initio calculations were carried out for the sake of analysis and interpretation. Thermal expansion has been calculated via the volume dependence of phonon spectra. Our analysis indicates that Ag phonon modes within the energy range 2 to 5 meV are strongly anharmonic and major contributors to thermal expansion in both systems. The application of pressure hardens the low-energy part of the phonon spectra involving Ag vibrations and confirms the highly anharmonic nature of these modes.

We report here our study on SiC doped with transition metals using first principle density functional theory calculations. We have considered cubic SiC with 3d transition metals as substitutional impurities for Si and C site separately. Cubic SiC doped with Cr, Mn, show ferromagnetism whereas with Sc, Ti, V and Co show site dependency of magnetic properties. Rests of the impurities are found to be non-magnetic., Presented in the 55th DAE-Solid State Physics Symposium, 26th to 30th December, 2010, Manipal University, Manipal, India; AIP Conf. Proc. 1349, 1087-1088 (2011)

Yttria (Y${}_{2}$O${}_{3}$) is a well-known ceramic material extensively used in industry. We report new neutron inelastic scattering measurement of the phonon density of states (PDOS) and lattice dynamic calculations using the ab-initio density functional theory and interatomic potential model, which are found to be in good agreement with each other. The model is then used in extensive free-energy calculation to understand the stability of various phases as a function of pressure and temperature. We find that one of the Y-O bonds shows a very large compression with increasing pressure, involving change of coordination around the Y atoms. This seems to provide the mechanism of the transition from the monoclinic phase to the hexagonal phase at the high pressure. We find that this transition is displacive in nature, and we also identify how the change of coordination affects the phonon spectra of the various phases.

In this work, we establish the bulk superconductivity of a high quality sample of monoclinic BiPd ($\alpha$-BiPd, space group P2$_1$) below 3.87 K by studying its electrical resistivity, magnetic susceptibility and heat capacity. We show that it is clean type-II superconductor with moderate electron-phonon coupling and determine its superconducitng and normal state parameters. Although $\alpha$-BiPd is a noncentrosymmetric superconductor with large electronic heat capacity (therefore, large $\gamma$), the effect of spin-orbit splitting of the electronic bands at the Fermi level is small. This makes little influence on the superconducting properties of $\alpha$-BiPd., Comment: 6 pages; 6 figures. Submitted to Phys. Rev. B

The dc‐bias field‐dependence of the complex dielectric permittivity in potassium dihydrogen phosphate (KDP) crystal has been studied across its ferroelectric transition temperature, revealing novel effects of the applied field on the domain wall dynamics. Exactly at the domain‐wall freezing temperature Tf , the dielectric constant (e′) is dramatically field‐insensitive while the dielectric loss (e″) is maximally frequency‐dispersive. The relaxational behaviour of domain‐wall motion manifests double Arrhenius feature‐‐‐ evident for two types of domain‐wall kinetic evolution; their activation energies having opposite dependences on the applied field. Rao and co‐workers have reported using PFM to study the D‐W dynamics [1]. Our results on the bulk dielectric property using appropriate probe illustrate higher sensitivity, making the precision measurements of rather small effects, yet unreported in the KDP literature.

Structure and Impedance studies of single phase Ba(Mn0.5Nb0.5)O3 (BMN) are reported here. The equivalent circuit modeling of complex impedance data fits with parallel combination of a capacitor and resistor. The activation energy values are similar for impedance (conductance) and relaxation suggesting that, the mechanism involved is same. The substitution of Mn at the B‐site do not help in reducing dielectric loses due to oxygen vacancies and/or doping of holes.

In the present work we have studied the variation of LFMR as a function of the angle (θ) between the applied magnetic field and the plane of the film. DC magnetron sputtering was used for film preparation on LSAT single crystal substrates from Sm0.55Sr0.45MnO3 targets synthesized by the solid state reaction route. X‐ray diffraction confirmed the epitaxial nature of these films. These films have simultaneous ferromagnetic and metal insulator transition at ∼91 K. These films exhibit enhanced low field colossal magnetoresistance ∼99% at 3.6 kOe at 80 K. Huge anisotropy is observed in the MR, which decreases from ∼80% to 6% as θ increases from 0 to 90°. The evolution of the resistance as a function of time and the magnetic field at a constant temperature (T≈77 K) has also been studied.

Magnetisation studies on nickel nano particles of different sizes viz. 4 and 12 nm are reported. Magnetisation measurements showed a hump with peak temperature (Tmax) at 17.3 K in ZFC for both the samples with average grain size of 4 nm and 12 nm. AC Susceptibility measurements showed a systematic shift of Tmax to higher temperatures with increase of frequency. Hysteresis measurements showed two types of magnetic ordering possibly arising from core spins and disordered shell spins.

The nature of spin‐waves in the quasi‐two dimensional spin‐1/2 square‐lattice Heisenberg system Zn2VO(PO4)2 has been studied. The coexistence of diffuse magnetic scattering and three dimensional antiferromagnetic Bragg peaks in the neutron diffraction pattern below TN (= 3.75 K), indicates the presence of spin‐waves at T

AC susceptibility and DC magnetization measurements were performed to examine the effect of P substitution on the superconducting and critical properties of optimally doped PrOFe0.9Co0.1As superconductor. Although P substitution increases the superconducting phase fraction, the TC of the compound is found to decrease at a rate of ∼13 K/at%. The magnetic critical current density (JC) and irreversibility field (H*) for these compounds were measured, both of which were found to decrease dramatically with the increase in phosphorus substitution.

We have used the first principle density functional approach for analyzing the structural stability of GaAs nanocrystal (NC) in various possible phases like wurtzite (B4), NiAs (B8), zincblende (B3), CsCl (B2) and NaCl (B1). The study reveals that the stable B3 phase of bulk GaAs is unstable in its nanocrystal and better stabilizes in wurtzite (B4) type phase. The study has been performed using local density approximation (LDA) with the Perdew‐Zunger(PZ) parameterization and Perdew‐Burke‐Ernzerhof(PBE) and Revised Perdew‐Burke‐Ernzerhof (revPBE) parameterization of the GGA potential. The calculated lattice parameter of bulk GaAs is in close agreement with its experimental counterpart.

CeOFeAs is a versatile oxy‐arsenide which shows a variety of electrical and magnetic properties. Superconductivity in this system has been achieved by doping electrons through different ionic substitutions by sealed tube reactions at ∼1100 °C. The superconducting transition temperature (Tc) and upper critical field (Hc2) could be optimized by substitution of suitable ions at Ce, O and Fe site. The highest Tc obtained was ∼49 K in a Y‐doped CeO0.9F0.1FeAs.

In this paper, we report the structural, magnetic and magnetotransport properties of (Pr0.7Sr0.3MnO3)1−x/NiOx (x = 0, 0.05, 0.10, 0.15 and 0.20) composites samples. The composite samples have been synthesized in such a manner so that there is no reaction between Pr0.7Sr0.3MnO3 (PSMO) and NiO. This has been confirmed by XRD and FESEM results. The magnetic measurements show reduction in ferromagnetic ordering in the composite samples with increasing level of NiO. Furthermore, incorporation of NiO phase into Pr0.7Sr0.3MnO3 matrix lowers the metal‐insulator transition temperature (TIM) and increases the resistance of composites. An enhancement in magnetoresistance (MR) is observed at low temperature, below 140 K, for the composites with x = 0.05, 0.10 and 0.15 and at high temperature (298K) for all the composites at applied magnetic field H = 5 kOe. It is suggested that the higher value of MR at temperature below 140 K is low field magnetoresistance (LFMR) caused by spin polarized tunneling, whereas at around...

Structural and magnetic measurements were performed on half doped polycrystalline manganite, Eu0.5Pr0.5MnO3. Reitveld refinement of the X‐ray powder diffraction pattern at room temperature suggests considerable Jahn‐Teller distortion. Investigation indicates a disordered antiferromagnetic ground state with a competition between antiferromagnetic and ferromagnetic interactions. A signature of spin frustration is encountered in the ac response.

The pressure induced structural phase transition and elastic properties of lutatium monopnictides LuX (X = N, P, Bi) have been studied using the first principles density functional theory within the generalized gradient approximation. The present work indicates that there is a structural phase transition from their ambient NaCl‐ (B1) structure to CsCl‐ (B2) structure at 299, 105 and 27 GPa along with the volume collapse of 4.7, 6.8 and 7.0%, respectively. Structural parameters like lattice constant (a0), bulk modulus (B) and pressure derivatives of bulk moduli (B′) are presented. We also report the second order elastic constants for these compounds.

The electrical resistivity and thermopower of the parent manganites LaMnO3, NdMnO3, and PrMnO3 is analyzed within the framework of the small polaron conduction. The high temperature state of RMnO3 compounds documents that the charge carriers are localized as small polarons. This enables one to estimate the activation energy for both the resistivity and thermopower properties. The activation energy increases with the decrease in ionic radii from La to Nd in parent manganites. Deduced polaron activation energy shows that it is low for LaMnO3 as compare to PrMnO3, and is attributed to reduce disorder state in LaMnO3 as compared to PrMnO3.

Magnetic behaviour has been reported for lanthanum doped gadolinium orthochromite, La0.1Gd0.9CrO3 in the temperature range 20 K–300 K. Distinct negative magnetization is exhibited by field cooling measurements while zero field cooling measurements show only positive magnetization. This arises due to superposition of magnetization of canted Cr3+ sub‐lattice and Gd3+ moments aligned in opposite directions under combined effect of external field and an internal field of ordered Cr3+ sub‐lattice. Estimated values of Cr3+ moments, internal field due to sublattice of canted ordered Cr3+ and the paramagnetic Curie temperature of Gd3+ sub lattice show strong dependence on external magnetic field. Magnetization‐field curves below TN show small hysteresis with the reduction in anisotropy below a certain temperature.

We present results of Raman study on epitaxial Fe3O4 films grown in three different orientations (100, 110 and 111) on MgO (100), MgO (110) and c‐axis Al2O3 substrates respectively. X‐ray diffraction and in‐plane (φ scan) measurements indicate that films are epitaxial and single phase in nature on all the three substrates. Using Allen’s formula, the strength of the electron‐phonon coupling (λ) is estimated with the help of frequency and line width of different Raman modes. The observed variation in λ value in epitaxially grown film in different orientation indicates the anisotropic behavior of electron ‐phonon coupling constant.

Condensed matters can be expanded into negative pressure states. Although these states are metastable, their long life‐time makes them appropriate for experimental investigations. Some relevant behaviour of liquids and solids under negative pressure will be reviewed.

The effect of Bi on the structural and optical properties of Se82−xBixTe18 glassy alloys is studied, theoretically. Cohesive energy is calculated by using chemical bond approach and is found to decrease with increasing Bi content. Optical band gap of thin films is calculated by Shimakawa’s relation. The optical band gap decreases with increase in Bi content.

We report ab initio calculations of the phonon spectra for hafnium nitride (HfN) at ambient and high pressures. The calculation of phonon density of states using the density functional perturbation theory including external perturbations like strains and electric fields in periodic systems carried out for full Brillouin zone. The lattice constant obtained for the HfN is in agreement with the experimental value. The calculated pressure variation of the phonon density of states show trend similar to the pressure dependent Raman spectra. The results regarding zone‐center phonon modes for HfN shows generally good agreement with Raman measurements phonon.

Series of nanocrystalline Cu1−xZnxFe2O4 (x = 0.2, 0.4, 0.6 and 0.8) spinel ferrites have been synthesized using advanced sol‐gel method. The XRD measurements confirm the formation of cubic spinel structure in single phase for all the samples and the average particle sizes are 14–18 nm. In this paper the dc magnetization study for one sample Cu0.4Zn0.6Fe2O4 is reported. The nanocrystalline sample is superparamagnetic above the blocking temperature of 180 K. The reduction in saturation magnetization is attributed to disordered magnetic moments at surface around the core of nanoparticles.

The spin dependent momentum densities in Ni2MnSn Heusler alloy have been measured at 10 and 300 K using magnetic Compton scattering. For these measurements, we have used 182.79 keV circularly polarized synchrotron radiation at SPring8, Japan. Spin dependent electron momentum densities are analyzed in terms of Mn 3d, Ni 3d and itinerant electrons to calculate their role in formation of net spin moment. Magnetic moments at different sites of constituent atoms have also been compared with the present full potential linearised augmented plane wave calculations and other available data.

Nano dimensional effect on magnetic, electronic and magneto‐transport properties of granular ferromagnetic insulating Pr0.8Sr0.2MnO3 (PSMO) manganites showing two magnetic phase transitions, paramagnetic to ferromagnetic transition at higher temperature (∼150 K) followed by a ferromagnetic to antiferromagnetic transition below 45 K has been investigated in detail. While the high temperature transition is found to increase with the decrease of particle size, the low temperature transition is smeared. In the electronic transport, though, the bulk sample shows insulating nature throughout the temperature range, while surprisingly, its nanometric counterpart, shows metal‐insulator transition at around 150 K. The magnetoresistance (MR) of the nanometric sample is found to be very high (∼90%) at 8 Tesla at 2 K compared to the MR of the bulk sample (∼40%). We have analyzed the DC magnetization, ac‐susceptibility, electronic‐, magneto‐transport and other results in nano mangaanites on the basis of enhanced surfac...

BiMn2O5, prepared by high energy ball milling of precursor oxides followed by sintering at 900° C for 24 h, has been investigated for its magnetic and electrical properties. The XRD pattern reveals orthorhombic phase with Pbam space‐group. Magnetization measurements show a paramagnetic behaviour at room temperature with a Neel transition at 40 K. Electrical conductivity studies show room temperature resistivity value around 9×105Ωcm.

Real time intrinsic stress behavior of Co‐film on p‐Si (100) suggests that the Co film is composed of Co grain with large grain boundaries. This granular system shows an appreciable change of magnetoresistance (MR). The current voltage (I–V) measurement of the Co/Si interface shows a rectifying behavior, having ideality factor 5.86 and Schottky barrier height (SBH) of 0.61 eV. At low temperature (∼10 K) under zero and non‐zero magnetic field at forward bias (+5 V) the device shows spin‐valve like behavior.

The present work reports electrical properties of ZrSTe crystals gown by direct vapour transport method. To find out resistivity we have performed two probe resistivity measurements and Hall coefficient, mobility as well as carrier concentration are obtained by Hall effect measurements along the cleavage plane of as grown ZrSTe crystals. We report thermoelectric power of ZrSTe crystals in temperature range 313K‐573K. Data of Hall coefficient and thermo electric power have good agreement and indicates the semiconducting behavior of ZrSTe crystals.

Charge transport is dynamically and strongly linked with atomic structure, in nanostructures. We report our ab‐initio calculations on electronic transport through atomic chains and the model calculations on electron‐electron and electron‐phonon scattering rates in presence of random impurity potential in a quantum well and in a quantum wire. We computed synthesis and ballistic transport through; (a) C and Si based atomic chains attached to metallic electrodes, (b) armchair (AC), zigzag (ZZ), mixed, rotated‐AC and rotated‐ZZ geometries of small molecules made of 2S, 6C & 4H atoms attaching to metallic electrodes, and (c) carbon atomic chain attached to graphene electrodes. Computed results show that synthesis of various atomic chains are practically possible and their transmission coefficients are nonzero for a wide energy range. The ab‐initio calculations on electronic transport have been performed with the use of Landauer‐type scattering formalism formulated in terms of Grben’s functions in combination w...

In the present study, we provide the origin of the large Seebeck coefficient (S) within the framework of narrow band model in NaxCoO2. It is revealed that the bandwidth and asymmetry involved in narrow bands offer a reasonable explanation to the large and anomalous temperature variation of Seebeck coefficient of NaxCoO2 system, and our results represent an alternative view in understanding the thermoelectric properties of these materials.

The electronic, structural, mechanical and thermal properties of strongly correlated HoSb in the stable Fm3m and high‐pressure Pm3m phases have been analyzed using full‐potential method at normal and high pressures. The spin polarized Local Spin Density Approximation (LSDA) based on exchange‐correlation energy optimization has been used for calculating the total energy using WIEN2K code. The structural properties viz., equilibrium lattice constant, bulk modulus and its pressure derivative agree well with the available experimental data. The electronic structures have been obtained with the LSDA and LSDA+U approach. The LSDA+U strategy shows significant impact on the energy levels of the occupied and unoccupied 4f states of HoSb.

The prototypical Sm1−xSrxMnO3 has been extensively studied in order to understand the role of disorder on the nature of ferromagnetic (FM) to paramagnetic (PM) phase transition in narrowband manganites. It is shown that both the magnetic and structural properties of Sm1−xSrxMnO3 are extremely sensitive to the applied external pressure (P) and magnetic field (H). It is reported that TC increases and the width of the thermal hysteresis in magnetization and resistivity decrease rapidly with increasing P. Above a critical value of P, the hysteresis disappears completely and the transition becomes second order. Such a strong dependence of magnetic properties on P clearly indicates that magnetic and structural order parameters are strongly coupled in this system and there exists a critical end point of the first order FM transition. To confirm the transition becomes conventional second order above the critical point, the system should obey the critical behavior belonging to some universality class, the most imp...

Optical dielectric function and absorption coefficient of FeS2 are computed using ab initio full potential linearized augmented plane wave method within the density functional approximation. Our band structure calculations show a direct band gap of 0.68 eV. Different peaks in the dielectric function are explained in terms of interband transitions in the energy bands. On the basis of present optical properties, a potential use of FeS2 in photovoltaic applications is also discussed.