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In this paper, we show that the Grotzsch graph Gz has admits Vertex Prime Labeling. When the graph has Vertex Prime Labeling that graph is called Vertex Prime graph. A Graph G = (V, E) is said to have a Vertex Prime Labeling if its edges can be labeled with distinct integers from {1,2,3,⋯, |E|} such that for each vertex of degree at least two, the Greatest Common Divisor of the labels on its incident edges is 1. We also prove that Vertex Prime Labeling in the context of the operation of duplication.

In this article, thermopower study of the polycrystalline TiSe2 and its Fe intercalated TiSe2 has been analyzed in detail. TiSe2 is two dimensional material which formed in hexagonal crystal structure having space group p3m1(164). Temperature dependent resistivity shows a considerable shift in Charge Density Wave (CDW) transition temperature towards low temperature with vanishing CDW peak intensity. The thermopower data shows peak or dip indicating the existence of CDW hybridization and this is in line with the electrical transport data. A scaling has been done in thermopower data by normalization which can be understood in terms of variation of hybridization across the CDW transition. Further, the temperature dependent thermopower data is well fitted using Nordheim-Gorter rule by Two Band Model (TBM). The results of the fittings indicate a drastic decrease of activation energy upon Fe intercalation in TiSe2 in semiconducting counterpart. Moreover, Diffusion thermopower corresponding to the metallic part is systematic as far as carrier compensation is concerned.

Heusler compound (Co1-xCrx)2CrAl for x=0 and 0.2 have been prepared by arc melting process. Room temperature XRD patterns of both compounds indicate single phase Cu2MnAl like L21 structure with B2 disorder. Resistivity measurement by varying temperature from 8-300K indicates metal like behavior of all compounds. At high temperature (above 150K) resistivity for both compounds linearly increases with increasing temperature. At low temperature region (≈8-40K) nonlinearity is observed in resistivity vs. temperature plot because of unconventional one-magnon scattering and two-magnon scattering that indicates half-metallic nature of both compounds. Magneto-resistance (MR) at 10K and 300K with varying magnetic field from 0-12 Tesla for both compounds have positive value but do not follow H2 dependency. The MR value at 10K at 12 Tesla magnetic field for the compound x=0 is 7.3% and for x=0.2 is 4.98%.

In the present work, influence of Sb doping on magneto transport properties of the topological insulator Bi1−xSbx in its nano crystalline form, prepared by microwave assisted solvothermal synthesis, is investigated. At a fixed temperature of 4K, for x=0.06, a positive linear magneto resistance (PLMR) at low magnetic fields was observed, which transforms towards a parabolic classical MR curve with a further increase in Sb molar ratio x. The slope of MR was found to increase with x, the deviation from linearity was found to be attributable to a monotonic decrease in average carrier mobility as well as a systematic increase in the carrier concentration (electron- hole) asymmetry ratio. This elucidates on a possible mechanism for tuning of MR by varying carrier concentration as well as mobility and hence is likely to be instrumental in development of MR dependent devices.

Here, we report the synthesis and characterization of the Nb2Pd(S0.9Te0.1)5 superconductor. The resultant polycrystalline sample is consists of solid chunks along with mesh of fibers which are grown in thin long rod shapes having length in several millimeters with cross-sectional area around 5x3 µm2. The normal state of this superconductor behaves abnormally compared to its parent compound (Nb2PdS5) which is shown here. In high temperature regime (T > 125K) it follows the power law which is completely different from its parent analog which shows metallicity (linear behavior) in high temperature range. Below this temperature region a broad peak appears centered around T* ≈ 62K, the origin of this anomaly is unknown right now, followed by a dip which is centered around T’ ≈ 23K which may be some sort of electron localization or some gap like excitation which preceding the superconducting transition having onset at Tc (onset)≈ 6.7K. The upper critical field value Hc2(0) = 52.24T enhances in these superconducting fibers. Aslamazov-Larkin (AL) theory shows three significant (3D, 1D and short-wave (SW)) fluctuation regimes in these superconducting fibers.

Transport and calorimetric property has been investigated down to 2K. It suggests the absence of magnetic ordering down to the lowest temperature and is at par with the normal metallic behavior. However, the Sommerfeld coefficient (γ) and the T2 coefficient ‘A’ from the resistivity measurements under zero field suggests small electron-electron correlations in comparison to MnSi. There is a negligible change in the physical properties with the application of magnetic field of the order 10T. Resistivity and Heat capacity in zero field suggests the Fermi liquid ground state of the compound.

Bi2Te3 nanomaterials were grown by microwave synthesis technique. Resistivity of the material shows semiconducting like nature which has been interpreted by thermally activated behavior in the high temperature range, three dimensional variable range hopping (VRH) mechanism in the middle range and combined effect of both electron-electron interaction and weak antilocalization(WAL) in the lower temperature regime from 10K to 2K. Full cycle magnetoresistance (MR) at 2K of the material exhibits WAL effect that evolves smoothly in to a linear positive magneto resistance (LPMR) up to 10K, thereafter to a simple parabolic nature with respect to magnetic fields. These features unequivocally provide evidence for the so called topological surface states (TSS) in Bi2Te3 even in its nanocrystalline form.

Magnetotransport and thermal properties of microwave-synthesized nanostructured Bi2Te3, a well-known material of topological interest, have been studied in detail. Temperature-dependent resistivity shows a disordered metal-like behavior at high temperature with unsaturated ln(T)-dependent upturns at low temperature manifesting localization tendency. The slopes (κ) of the normalized conductivity (Δσ) vs ln(T) curves change sharply with magnetic fields upto 1 T and then saturate at a certain higher field (Bϕ), which is an indication of a combined electron–electron interaction and quantum interference effect (QIE) dominated transport. A noteworthy result is a crossover from positive to negative Coulomb screening factor (F) in Bi2Te3. Low-field (H ≤ 1 T) magnetoconductivity at low temperature follows a 2D Hikami–Larkin–Nagaoka equation, thereby revealing the QIE and associated dephasing nature of the electronic states at high temperatures. High-field (14 T) magnetoresistance (MR) at 2 K shows interesting features like low-field weak antilocalization, possibly a defect-induced negative MR that vanishes after post-annealing treatment, and a high field parabolic character in place. The Seebeck coefficient (S) is negative and varies quasilinearly with a slight but notable slope change at intermediate temperatures. Heat capacity measurements are in line with a narrow gap degenerate semiconductor with a low θD of 140 K. A combined analysis of heat capacity and thermopower reveals the localization of carriers at low temperatures and is in line with transport data.

We have investigated the magnetic and magnetocaloric properties of van der Waals (vdW) layered CrCl3 from magnetization and heat capacity measurements. CrCl3 exhibits complicated magnetic properties due to the strong competition between the ferromagnetic and antiferromagnetic interactions: a ferromagnetic ordering around 17 K followed by an antiferromagnetic ordering at 14.3 K. A large magnetic entropy change (− Δ S M) of 19 J kg−1 K−1, an adiabatic temperature change ( Δ T a d) of 6.2 K, and a relative cooling power of 600 J kg−1 are observed for a field change of 7 T near the transition temperature, and the mechanical efficiency (ηm) at 18 K and 0–3 T is 1.17. These values of magnetocaloric parameters are significantly larger than those for CrI3 and other layered vdW systems. The scaling analysis shows that all the rescaled Δ S M(T, H) data collapse into a single curve, which indicates the second order nature of magnetic phase transition. The above results suggest that environmentally friendly CrCl3 can be a phenomenal alternative to very expensive rare-earth material for the magnetic refrigeration for liquefaction of hydrogen.

Studies on thermal and transport properties of topologically interesting polycrystalline ZrTe5 down to 2 K and magnetic fields up to 14 T are reported here. Attempts have been made to explain the metal insulator transition-like features seen in magnetic fields, a behavior characteristic of ZrTe5. The maximum in relative magnetoresistance (MRmax) for a particular magnetic field with respect to the peak temperature, i.e., Tp(B), shows an activated behavior reminiscent of polaronic conduction seen upon chemical substitution like Hf in Zr. Magnetoresistance is well described by a small polaron hopping transport model in a systematic way for various fields. The estimated activation energies are in line with infrared spectroscopy as well as hole dominated thermopower supported by heat capacity measurements. The essential features of the analysis include square root dependence of magnetoresistance with the magnetic field possibly due to the weak antilocalization effect as well as T3/2 dependence on mobility, extracted from a simplified two-band model fit in magnetoresistance curves.

We report the results of structural, electrical, surface morphological, and magnetic studies on the undoped and dilute Fe (0.05) doped InSb films (In0.95Fe0.05Sb) using the grazing angle X-ray diffraction technique, the quantum design physical property measurement system, atomic force microscopy (AFM), magnetic force microscopy (MFM), and the quantum design magnetic property measurement system. The In0.95Fe0.05Sb film of 500 nm thickness is grown on the silicon (Si) substrate using the thermal evaporation technique. A systematic investigation of electrical resistivity as a function of temperature and magnetic field is embarked. The electrical resistivity of the respective sample exhibits an upturn at approximately 15 K in the ferrimagnetic region. This theory explains the anomalous behavior of the electrical resistivity based on electron-electron, electron-phonon, electron-magnon, and Kondo-like spin-dependent scattering. The high-temperature data above 300 K are interpreted using the adiabatic small polaron hopping model. The AFM study shows the uniform particle size distribution, whereas the magnetic interaction at the surface is seen through MFM. The zero-field cooled magnetization measurement shows the transition at ∼65 K. The hysteresis curve at 10 K shows the ferrimagnetic behavior of the In0.95Fe0.05Sb film with coercivity and residual magnetization values of ∼100 Oe and 6.8811 emu, respectively.

The effect of oxygen partial pressure (OPP) during deposition on the structural and ferroelectric properties of epitaxial SmFeO 3 (SFO) thin films is studied in the present report. The thin films are deposited using the pulsed laser ablation method. Two (00l) oriented substrates, viz., LaAlO 3 (LAO) and niobium doped SrTiO 3 (Nb:STO), are used for the deposition of films with 35 and 170 nm thicknesses at different OPP values. The prepared films are found to be of single phase and grow in the out-of-plane configuration SFO(hh0)/LAO(00l) using x-ray 2 θ − ω and ϕ scans. The epitaxial relationship between the substrate and the film, domain twinning, is confirmed by reciprocal space map measurements. Films of higher thickness exhibit tilted twin structures, more prominently for the films prepared at lower OPP. A significant change in the leakage current is observed as a function of OPP, and the results are explained in terms of the microstructure of the films.The effect of oxygen partial pressure (OPP) during deposition on the structural and ferroelectric properties of epitaxial SmFeO 3 (SFO) thin films is studied in the present report. The thin films are deposited using the pulsed laser ablation method. Two (00l) oriented substrates, viz., LaAlO 3 (LAO) and niobium doped SrTiO 3 (Nb:STO), are used for the deposition of films with 35 and 170 nm thicknesses at different OPP values. The prepared films are found to be of single phase and grow in the out-of-plane configuration SFO(hh0)/LAO(00l) using x-ray 2 θ − ω and ϕ scans. The epitaxial relationship between the substrate and the film, domain twinning, is confirmed by reciprocal space map measurements. Films of higher thickness exhibit tilted twin structures, more prominently for the films prepared at lower OPP. A significant change in the leakage current is observed as a function of OPP, and the results are explained in terms of the microstructure of the films.

Electroluminescence from heterojunctions fabricated by depositing ultrathin films of nanocrystalline CdS and ZnS on porous silicon by the liquid–liquid interface reaction technique is reported. Junction current–voltage characteristics were studied for different thicknesses of the deposited films. Large forward currents on the order of 180 mA/cm2 and a rectification ratio on the order of 103 were characteristic of the diode. The reverse breakdown voltage on the order of 150 V indicated the stability of these diodes. Electroluminescence was observed to arise at around 625 nm, which was blueshifted as compared to the photoluminescence peak and showed much smaller full width at half maximum (∼40 nm).

Nearly exponentially decaying heat capacity was observed exceptionally in a well-characterized naturally assembled hexagonal closed packed lattice of 4.0 nm nickel nanoparticles (NPs). It was also associated with quantum jumps. These were however not observed in other NP sizes and have negligible effects of high magnetic fields. Magnetic susceptibilities in contrast revealed the evolution of quantum size effects with a decrease in particle size. They exhibited sharp rise below about 30 K and vestiges of saturations below 5 K. The sharp rise was explained by Curie-like characteristics of odd electrons, while the saturations tend towards the orthogonal even-like case.

Topographical evolution of 100 MeV Au8+-ion-irradiated InP surfaces was studied using atomic-force microscopy (AFM). The surfaces were roughened under dense electronic excitations. Root-mean-square roughness measured from AFM studies showed an exponential saturation behavior with fluence. Sample temperature during irradiation was found as a parameter to control the amount of roughness on the surface and the evolution of irradiated surface topography is discussed in terms of thermal spike model. © 2001 American Institute of Physics.

Modification on Si (111) surface resulting from 200 MeV 107Ag+14 ion irradiation at an incidence angle of 15° with respect to the surface normal has been investigated by atomic force microscope (AFM) and x-ray diffraction techniques. Root mean square roughness measured using AFM was found to increase from 0.96 nm in the pristine sample to 18.33 nm in the sample irradiated with an ion fluence of 5×1013 ions/cm2. This spectacular increase in surface roughness is ascribed to the displacement of Si atoms driven by the creation of unsaturated dangling bonds on the Si surface during swift heavy ion irradiation. At a fluence of 5×1013 ions/cm2, a new type of ditch and dike structure was observed. These structures were distributed over the irradiated surface. Each ditch is followed by a dike. This is attributed to the cumulative effect of ion irradiation arising due to overlapping of ion-induced damaged zones and electronic excitation-induced shear motion of the atoms towards the surface.

The design and fabrication of a fully automated, computer controlled, precise measurement system for sound velocity and internal friction using the vibrating reed technique is described in detail. Relative variation of sound velocity and internal friction has been measured using automatic frequency locking. A detailed description of the apparatus is given. The associated electronics that took care of quite a few problems in getting a good lock-in condition have been highlighted. With a bath cryostat and sample insert, measurements were made down to liquid helium temperatures with a temperature control accuracy better than 10 mK. The resonance frequency and the peak amplitude were recorded as a function of temperature which in turn provided temperature variation of sound velocity and internal friction with a relative accuracy better than 1 part in 104 and 1.5%, respectively. Precise nature of the results obtained using this setup is highlighted for a specimen of an amorphous alloy near it’s Curie temperature.

A fully automated precise electrical resistance measurement system for more than one sample has been constructed. Conventional four‐probe measurements with van der Pauw and Montgomery configurations are possible with this system. Resistance measurements in the range of a few μΩ to a few GΩ are possible for six samples at a time from room temperature down to liquid‐helium or liquid‐nitrogen temperatures with a temperature control accuracy of better than 10 mK. The design features of the system with special reference to the low‐noise switching methods of currents and voltages are described in detail. Precision of the results thus obtained using this system are highlighted for a few superconducting and semiconducting samples.

Resonant dipolar relaxation in poly( e-caprolactone) (PCL) is reported using thermally stimulated discharge current spectroscopy. PCL is a bio-medically known shape memory polymer having a well defined γ, β, α, and α′ relaxations, respectively, centered around 125 K, 170 K, 220 K, and 270 K as seen by the measurements. By employing a new protocol variable poling temperature at constant freezing temperature, resonant dipolar relaxation in PCL could be induced, especially in the vicinity of α relaxation. Such a protocol is useful in de-convoluting the features in a more meaningful fashion. By an analysis of activation process, we could show a clear contrast enhancement of the dynamics of the participating dipoles by means of a minimum in the activation energies situated around the glass transition region. The relevant parameters of interest such as activation energies and relaxation times are estimated and discussed.

We studied localized surface plasmon resonances (LSPR) at different compositions, substrate temperatures, and mass thicknesses of Ag-Au alloy nanoparticle films grown by sequential pulsed laser deposition. The LSPRs were pronounced at all compositions of the films grown at high substrate temperature of about 300 °C as compared to those grown at room temperature. The alloy formation and composition of the films were determined using X-ray photoelectron and energy dispersive spectroscopy. Films' mass thickness and compositional uniformity along the thickness were determined using X-ray reflectometry and secondary ion mass spectroscopy. Atomic force microscopic analysis revealed the formation of densely packed nanoparticles of increasing size with the number of laser ablation pulses. The LSPR wavelength red shifted with increasing either Au percentage or film mass thickness and corresponding LSPR tuning was obtained in the range of 450 to 690 nm. The alloy dielectric functions obtained from three different models were compared and the optical responses of the nanoparticle films were calculated from modified Yamaguchi effective medium theory. The tuning of LSPR was found to be due to combined effect of change in intrinsic and extrinsic parameters mainly the composition, morphology, particle-particle, and particle-substrate interactions.

Present study reveals that the length-scale of phase separation in La5/8-yPryCa3/8MnO3 thin films can be controlled by strain disorder invoked during the growth and relaxation process of film. Strain disorder provides an additional degree of freedom to tune colossal magnetoresistance. Magneto-transport measurements following cooling and heating in unequal fields protocol demonstrate that coherent strain stabilizes antiferromagnetic insulating phase, while strain disorder favors ferromagnetic metallic phase. Compared to bulk, antiferromagnetic-insulating phase freezes at lower temperatures in strain disordered films. Raman spectroscopy confirms the coexistence of charge-ordered-insulating and ferromagnetic-metallic phases which are structurally dissimilar and possess P2(1)/m and R-3C like symmetries, respectively. (C) 2015 AIP Publishing LLC.

In this paper, we report on physical properties of pure and Cu doped cadmium telluride (CdTe) films deposited onto corning 7059 microscopic glass substrates by electron beam evaporation technique. X-ray diffraction study showed that all the deposited films belong to amorphous nature. The average transmittance of the films is varied between 77% and 90%. The optical energy band gap of pure CdTe film is 1.57 eV and it decreased to 1.47 eV upon 4 wt. % of Cu addition, which may be due to the extension of localized states in the band structure. The refractive index of the films was calculated using Swanepoel method. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (Ed) parameters, dielectric constants, plasma frequency, and oscillator energy (Eo) of CdTe and CdTe:Cu films were calculated and discussed in detail with the light of possible mechanisms underlying the phenomena. The variation in intensity of photoluminescence band...

We investigated the effect of magnetic (Mn) and nonmagnetic (Ga) doping at the Cr site of the layered geometrically frustrated antiferromagnetic compound LiCrO2. 10% Ga doping at the Cr site does not invoke any metastability typical of a glassy magnetic state. However, similar amount of Mn doping drives the system to a spin glass (SG) state which is particularly evident from the magnetic memory and heat capacity studies. The onset of glassy state in 10% Mn doped sample is of reentrant type developing out of higher temperature antiferromagnetic state. The SG state in the Mn-doped sample shows a true reentry with the complete disappearance of the antiferromagnetic phase below the SG transition. The lack of SG state on Ga doping indicates the importance of random ferromagnetic/antiferromagnetic bonds for the glassy ground state in LiCrO2.

Epitaxial thin films of GaFeO3 (GFO) with different thicknesses (22–170 nm) are prepared on (001) oriented yttria-stabilized zirconia substrate using pulsed laser deposition. The M-H data measured below Curie temperature (TC) mimic two phase composite magnetic system consisting of hard and soft magnetic phases. The results are explained in terms of Fe distribution among the available cation sites of GFO. Thermo-magnetic irreversibility and cusp in zero-field cooled magnetization are observed for all the films and are explained in terms of the magnetic anisotropy of the GFO.

Silver incorporated tungsten oxide thin films are prepared by RF magnetron sputtering technique. The effect of silver incorporation in micro structure evolution, phase enhancement, band gap tuning and other optical properties are investigated using techniques such as x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and UV-Visible spectroscopy. Effect of silver addition in phase formation and band gap tuning of tungsten oxide thin films are investigated. It is found that the texturing and phase formation improves with enhancement in silver content. It is also found that as the silver incorporation enhances the thickness of the films increases at the same time the strain in the film decreases. Even without annealing the desired phase can be achieved by doping with silver. A broad band centered at the wavelength 437 nm is observed in the absorption spectra of tungsten oxide films of higher silver incorporation and this can be attributed to surface plasmon resonance of silver atoms present in the tungsten oxide matrix. The transmittance of the films is decreased with increase in silver content which can be due to increase in film thickness, enhancement of scattering, and absorption of light caused by the increase of grain size, surface roughness and porosity of films and enhanced absorption due to surface plasmon resonance of silver. It is found that silver can act as the seed for the growth of tungsten oxide grains and found that the grain size increases with silver content which in turn decreases the band gap of tungsten oxide from 3.14 eV to 2.70 eV.

We report the effect of strontium (Sr) doping on dielectric, magnetization, and thermodynamic properties of polycrystalline Y1−xSrxMnO3 (x = 0.1, 0.2) samples prepared by conventional solid-state reaction method. The temperature dependent dielectric permittivity and specific heat curves noticeably show the anomalies near its magnetic transition point, i.e., Neel temperature (TN), which are probably generated by the frustrated Mn3+ spins (S = 2) on a triangular Mn lattice showing the magneto-electric coupling between the electric and magnetic orders. However, the magnetic transition is not clearly evident in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Y3+ spins. The electronic transport mechanism in these materials was analyzed within the framework of conventional Arrhenius Law, i.e., ρ(T) = C exp(Ea/kBT) applied to low frequency ac resistivity data, and through the peak method employed to the permittivity and loss ta...

We demonstrate the use of controlling the ambient during spin coating to finely control the solvent evaporation rate in order to obtain varying degree of phase separation in P3HT:PCBM blend films and study the effect on device performance. To understand the basic phenomenon driving the phase separation, modelling study has been performed, which show that the phase separation is due to PCBM diffusion towards the nucleation site once its solubility limit is crossed during spin coating process.

Self-assembled epitaxial nanostructures of NiFe2O4 ferrimagnetic material were grown in the matrix of CaCu3Ti4O12 dielectric material by pulsed laser deposition. SEM and AFM studies showed self-assembly of vertical columnar structures of NiFe2O4 in the matrix of CaCu3Ti4O12. The substrate induced strain in this nanocomposite system is insignificant and vertical strain induced by CaCu3Ti4O12 matrix material on the NiFe2O4 rods governs the strain state. Further, vertical strain state in NiFe2O4 is switched from tension to compression as a result of this geometry. A change in magnetization of the composite film is observed around 100 K where the dielectric constant also showed a sudden change.

The samples of Bi2Sr2Ca2Cu3-xMnxO10+δ (x = 0.0 to 0.30) were prepared by the standard solid-state reaction method. The phase identification characteristics of synthesized (HTSC) materials were explored through powder X-ray diffractometer reveals that all the samples crystallize in orthorhombic structure with lattice parameters a = 5.4053 Å, b = 5.4110 Å and c = 37.0642 Å up to Mn concentration of x = 0.30. The critical temperature (Tc) measured by standard four probe method has been found to depress from 108 K to 70 K as Mn content (x) increases from 0.00 to 0.30. The effects of sintering temperature on the surface morphology of Bi2Sr2Ca2Cu3-xMnxO10+δ have also been investigated. The surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM & AFM) results that voids are decreasing but grains size increases as the Mn concentration increases besides, nanosphere like structures on the surface of the Mn doped Bi2Sr2Ca2Cu3-xMnxO10+δ (Bi-2223) samples.

This paper reports an in-depth study on nanocrystalline Gd-doped ZnO thin films synthesized using versatile pulsed spray pyrolysis method and exhibit room temperature ferromagnetism. The detailed structural and microstructural studies confirm that the doped Gd ions occupy Zn sites and the peak shift can be elucidated by charge neutrality. Optical investigation shows that the Gd doping in ZnO lattice leads to a decrease in the near band edge position due to the introduction of new unoccupied states by Gd 4f electrons. The electronic structure of the Zn1−xGdxO at the O K edge shows the evolution of pre-edge spectral features similar to cuprates and manganites, and also confirms the strong hybridization of O 2p–Gd 4f/5d states. Furthermore, the Gd M5 edge provides evidence that Gd ions are in the trivalent state. Hysteresis measurements demonstrate that the Gd-doped ZnO films are magnetically anisotropic and exhibit intrinsic ferromagnetic behavior at room temperature. Higher magnetization in 3 kOe values is...

Here we report the optimized magneto-transport properties of polycrystalline La0.70Ca0.3-xSrxMnO3 and their composites with Ag. The optimization was carried out by varying the Sr and Ag contents simultaneously to achieve large temperature coefficient of resistance (TCR) as well as low field magneto-resistance (MR) at room temperature. Sharpest paramagnetic (PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the vicinity of the room temperature (TC=300 K=TIM) for the composition La0.70Ca0.20Sr00.10MnO3:Ag0.20. Partial substitution of larger Sr2+ ions at the Ca2+ ions sites controls the magnitude of the FM and IM transition temperatures, while the Ag induces the desired sharpness in these transitions. For the optimized composition, maximum TCR and MR are tuned to room temperature (300 K) with the former being as high as 9% and the later being 20 and 30 percent at 5 and 10 kOe magnetic fields respectively. Such sharp single peak (TCR= 9 percent) at room temperature can be used for the bolometric and infrared detector applications. The achievement of large TCR and low field MR at T~300K in polycrystalline samples is encouraging and we believe that further improvements can be achieved in thin films, which, by virtue of their low conduction noise, are more suitable for device applications., Comment: 11 pages Text + Figures. Suggestions/comments welcome (awana@mail.nplindia.ernet.in)

We have investigated the magnetic and magnetocaloric properties of HoMnO3 single crystal. HoMnO3 displays a series of complicated phase transitions due to the long range ordering of Mn3+ and Ho3+ moments. Field variation in magnetization generates a metamagnetic transition and produces an entropy change of 13.1 J/kg K at 7 T in the vicinity of antiferromagnetic ordering temperature of Ho3+. The values of adiabatic temperature change (∼6.5 K) and relative cooling power (∼320 J/kg) for a field change of 7 T are also appreciable to consider HoMnO3 as a magnetic refrigerant at low temperature.

The high field magnetization and magneto transport measurements are carried out to determine the critical superconducting parameters of MgB2-xCx system. The synthesized samples are pure phase and the lattice parameters evaluation is carried out using the Rietveld refinement. The R-T(H) measurements are done up to a field of 140 kOe. The upper critical field values, Hc2 are obtained from this data based upon the criterion of 90% of normal resistivity i.e. Hc2=H at which Rho=90%Rho; where RhoN is the normal resistivity i.e., resistivity at about 40 K in our case. The Werthamer-Helfand-Hohenberg (WHH) prediction of Hc(0) underestimates the critical field value even below than the field up to which measurement is carried out. After this the model, the Ginzburg Landau theory (GL equation) is applied to the R-T(H) data which not only calculates the Hc2(0) value but also determines the dependence of Hc2 on temperature in the low temperature high field region. The estimated Hc(0)=157.2 kOe for pure MgB2 is profoundly enhanced to 297.5 kOe for the x=0.15 sample in MgB2-xCx series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters like irreversibility field, Hirr and critical current density Jc(H) are also calculated. The nano carbon doping results in substantial enhancement of critical parameters like Hc2, Hirr and Jc(H) in comparison to the pure MgB2 sample., 25 pages with 9 Figs: comments/suggestions(awana@mail.nplindia.ernet.in)

We report here on a simple but precise thermoelectric power measurement setup that can be adapted for different environments. This setup has been extensively used for cryogen-free environment to measure a variety of samples. It is made simple to load and hold the sample between two copper blocks by a spring-shaft arrangement. The usable range of measurements is a few microV/K to a few hundreds of microV/K. The salient features of the setup in achieving good precision both in natural warm-up/cooldown and controlled measurements are (i) the continuous DeltaT control across the sample by a chromel-AuFe(0.07%) thermocouple and (ii) the measurements of emf generated across the sample and the thermocouple using a nanovoltmeter and a scanner system. The versatile nature of the setup is further demonstrated by employing it in a magnetic field environment up to 140 kOe. The precision achieved using this system is highlighted for a few systems of current interest.

Highly photoconducting β-In2S3 thin films with conducting grain boundaries were obtained, using “chemical spray pyrolysis” technique. By varying the atomic ratio of the precursor solution used for spray pyrolysis, the photoconductivity of these films could be tailored. Conducting grain boundaries were found only for samples with a specific stoichiometry and these films exhibited photoresponse to intrinsic and extrinsic excitation wavelengths in the range of 325–532nm. Postdeposition vacuum annealing of these films enhanced the grain boundary conductivity, caused the films to exhibit persistent photoconductivity for both intrinsic and extrinsic excitations and extended the extrinsic photoresponse to wavelengths beyond 632.8nm. Photoresponse to excitation wavelength of 632.8nm was observed in films with and without conducting grain boundaries which proved that the extrinsic photoresponse to this wavelength was an effect associated with the defect chemistry of the β-In2S3.

A simple technique of single shot x-ray microscopic imaging is reported using two simultaneously produced laser-plasma x-ray sources. Twin x-ray images are recorded by placing the sample in a proximity gap with a photoresist and exposing it to two equivalent point x-ray sources. Characterization of the technique is carried out using a carbon fiber as a test sample and x-ray emission (hν⩾1 keV) from laser produced copper plasmas. A spatial resolution of ∼300 nm is observed, consistent with the geometrical parameters of the imaging system. This method may be useful in obtaining a single shot comparison of spectral and temporal characteristics of a sample by using different x-ray filters or plasma targets for the two imaging paths and a temporal delay in generation of the two x-ray sources, respectively.