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In this paper, we investigate the impact of an external magnetic field on the Weibel instability driven by temperature anisotropy in a magnetized plasma. The study provides the influence of electron temperature anisotropy, considering both cold as well as warm ions. We derive expressions for the growth rate Γ (s−1) in each case to quantify the effect of some specific parameters on the instability. For example, the growth rate is plotted against the magnetic field for three distinct cases: considering only electrons, including cold ions, and incorporating warm ions. It is observed that the growth rate decreases as the applied magnetic field increases. Furthermore, the addition of both cold and warm ions to the plasma significantly influences the observed effects. It can be explained as follows: in the presence of cold ions, the growth rate is decreased with an increase in the wave number kz (cm−1). In addition, a decrease in the growth rate is observed with an increasing wave number in the case of warm ions. Therefore, it can be seen that the Weibel instability, propelled by thermal anisotropy, holds significant implications owing to its prevalence in both astrophysical and laboratory plasmas. The findings presented here are expected to contribute to the advancements in magnetic field generation and particle acceleration in various astrophysical phenomena, including gamma-ray bursts, relativistic collisionless shock fronts, radio supernovae, and pulsar winds. [ABSTRACT FROM AUTHOR]

We have carried out detailed investigations of magnetic ordering and the origin of exchange-bias phenomenology in polycrystalline 154Sm0.4Ca0.6MnO3 perovskite compound by employing dc and ac magnetizations, neutron depolarization, and neutron diffraction techniques. The neutron diffraction study reveals a broad charge ordering transition in the temperature range of 275-150 K, manifested by gradually varying structural distortions. DC magnetization and neutron diffraction studies infer a magnetic ordering around 110 K. Below ~40 K, this compound exhibits a large enhancement of the magnetization and an exchange-bias effect (~18 kOe at 5 K). The exchange-bias effect shows a characteristic temperature and cooling field dependence and a training effect. The compound undergoes a CE-type (checker-board type) antiferromagnetic (AFM) ordering of Mn3+/Mn4+ spins below 110 K. The large magnetization below ~40 K arises from the ferrimagnetic (FIM) ordering of a minority (~5 vol. %) non-perovskite phase of Mn3O4. The appearance of exchange bias is ascribed due to the presence of an interface, formed between the FIM (Mn3O4) phase and the main AFM perovskite phase. Our study has implications in giving new directions in the search of large exchange-bias effects in mixed FIM/AFM bulk systems. [ABSTRACT FROM AUTHOR]

Often, a depressed fill factor is observed in organic solar cells (OSCs), which is usually known as S-shaped current-voltage (J−V) characteristics. To investigate the origin of the depressed fill factor further, a poly[N-9-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)]:[6,6]-phenyl C71 butyric acid methyl ester based OSC has been characterized through impedance spectroscopy. In addition, the photocurrent vs the applied effective bias plot reveals that the S-shaped J−V characteristics primarily reduce the diffusion current of the device. The present study shows that the diffusion current dominated section of photocurrent reduces with a slope of 2 in the depressed fill factor section given that the slope may further increase as per the impact of the S-shape. The reduction in the diffusion constant (Dn) in the S-shaped region supports the decrease in the diffusion current, which is observed through the photocurrent analysis. It is observed that, in the S-shaped section of the current-voltage characteristics, the transport time for free carriers increases up to 443 μs. The larger Urbach energy for the active layer of an S-shaped device demonstrates higher subbandgap disorder. Therefore, it is concluded that the accumulation of the charge carriers within the device and disorder in the active layer leads to the S-shaped current–voltage characteristics as well as poor carrier extraction. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices. [ABSTRACT FROM AUTHOR]

Here, we demonstrate the effect of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and molybdenum trioxide (MoO3) hole transport layers (HTLs) on degradation of the bulk-heterojunction organic solar cell (OSC) with the combination of two active layers—poly(3-hexylthiophene) and poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]. The study is performed for unencapsulated conventional structure OSCs exposed to the ambient dark condition. In the self-life test situation, it is found that PEDOT:PSS based devices show an initial higher short circuit current and subsequent faster degradation with time in comparison to the MoO3 based devices. The effects of these HTLs have been shown in terms of better charge extraction and a decrease in the shunt resistance as well as the bulk resistance of the active layer. The charge carrier generation probability evaluated from photocurrent data shows the dominant impact of active layer degradation rather than the oxidation of a top electrode under the ambient condition. This suggested mechanism is further supported by impedance spectroscopy as well as the evaluated transit time, global mobility, and exciton dissociation probability, establishing that the degradation does not much affect the transport property of the active material. Rather, it affects more the carrier generation rate. The low hole extraction barrier in PEDOT:PSS based devices show small transit time and high global mobility compared to MoO3. It is found that during the degradation process, the bulk resistance of the device significantly increases, which reduces the diffusion current in the device. [ABSTRACT FROM AUTHOR]

In this manuscript, conventional and inverted organic solar cells based on P3HT:PC[60]BM have been explored to understand the effect of deep defect states on the open circuit voltage. The enhancement in the open circuit voltage in the inverted structure compared to the conventional structure has been comprehensively discussed in terms of density of defect states. To comply with the investigation, DC and AC measurements (impedance spectroscopy) at various temperatures have been performed extensively. Enhancement in open circuit voltage at low temperature is observed which is described by the shifting of hole and electron quasi-Fermi levels. The important observation from the defect density of states profile is that the center of Gaussian distribution is shifted to high energy as the temperature is increased which is an indication of the creation of shallow traps in polymers. In the inverted device, the disorder parameter (σ) is 33 meV, whereas in the conventional device it becomes 75 meV. This implies that the energetic disorder is reduced in an inverted device which helps in the improvement of open circuit voltage. [ABSTRACT FROM AUTHOR]

The Weibel instability due to temperature anisotropy of electrons and ions in a plasma in the presence of cold and warm ions is reported. Numerical calculations of the normalized growth rate are carried out when the frequency of electromagnetic waves is greater than or less than the thermal velocity of electrons for typical existing plasma parameters. The normalized growth rate increases with an increasing normalized wave number, and after attaining maxima, it decreases due to thermal effects. Therefore, a parabolic plot is obtained for the growth rate. The threshold values of the growth rate depend on the anisotropy parameters. On increasing the value of the temperature anisotropy ratio of either plasma component, the observed growth rate increases. There is a considerable and contrasting effect of the presence of cold and warm ions on the growth rate of the Weibel instability in the plasma. The addition of cold ions stabilizes the instability and reduces the maximum growth rate values, while the addition of warm ions to the plasma increases the instability with a considerable decrease in the domain of instability. Our theoretical investigations of the effect of temperature anisotropy on the growth rate of the Weibel instability are in good agreement with the existing experimental results. [ABSTRACT FROM AUTHOR]

In this article, the effect of dust charge fluctuations on the parametric upconversion of a lower hybrid wave into an ion cyclotron wave and a side band wave in a two-ion species tokamak plasma is studied. When the oscillatory velocity of plasma electrons is a few percent of the sound velocity, the lower hybrid wave becomes unstable and decays into two modes: an ion cyclotron wave mode and a low frequency lower hybrid side band wave. Furthermore, a ponderomotive force by a lower hybrid pump and a side band wave is exerted on the existing electrons, which drives the ion cyclotron decay mode. The presence of negatively charged dust grains and their shape, size, radius, and density influence the instability. The growth rate of instability is calculated by considering typical existing D–T (Deuterium–Tritium) dusty plasma parameters, and it is observed that the growth rate increases with the relative density of dust grains, number density of dust grains, oscillatory velocity of electrons, and amplitude of pump waves. However, the normalized growth rate increases with the unstable wave frequency, and it also increases as we increase the ratio of deuterium to tritium density. Here, the growth rate decreases with the increase in the size of dust grains and electron cyclotron frequency. The theoretical results summarized in the present study are able to efficiently elaborate the complexity produced in plasma properties in a tokamak due to the dust–plasma interactions, which are briefly discussed here. [ABSTRACT FROM AUTHOR]

We have observed the phenomenon of negative magnetization in spinel ferrites, CoCr2-xFexO4. The x = 0.15 compound lies in the interesting region of the composition (Fe) driven magnetic phase diagram as it shows two magnetic ordering temperatures along with a negative magnetization behavior. We have given a microscopic experimental proof of magnetic sublattice decoupling and temperature-induced negative magnetization using the neutron diffraction technique. The present study supports the Belov's hypothesis of a “weak” magnetic sublattice for an explanation of negative magnetization, where the “weak” octahedral sublattice deviates from the Brillouin function type behavior of sublattice magnetization as envisioned by Néel in his theory of ferrimagnetism. A physics concept for a possible application of such a negative magnetization phenomenon in spin transfer torque based magnetic random access memory has been outlined. [ABSTRACT FROM AUTHOR]

The effect of fluctuations of dust grains on the parametric up conversion of lower hybrid waves into a whistler wave in a complex plasma is studied. In a complex plasma, which contains ambient magnetic field, the lower hybrid pump possessing a large amplitude decays into two modes: a whistler wave mode and a lower hybrid wave mode having low frequency. Furthermore, a ponderomotive force is exerted by the lower hybrid pump and whistler side bands on the existing electrons, which drives the lower hybrid decay mode. Furthermore, the coupling of v ⃗ 1 , the oscillatory velocity of low-frequency lower hybrid waves, along with the density perturbations, produces a nonlinear current, which drives the whistler mode. The growth rate Γ (sec−1) of lower hybrid waves scales linearly with the amplitude of the pump waves, and it increases as the amplitude of the lower hybrid pump waves increase. Moreover, the dust grain charges influence the instability appreciably. Our theoretically observed growth rate decreases with the increase in the relative density d = n 0 i / n 0 e of negatively charged dust grains, while it decreases with the size of dust grains a (μm). The growth rate varies inversely to the electron cyclotron frequency ωce, and it decreases as ωce increases. The results presented in the article are efficiently able to elaborate the basics of the whistler wave excitation in complex plasmas, space plasmas, processing in solid state plasmas, fusion plasmas, and laboratory plasmas as well as industrial plasmas. [ABSTRACT FROM AUTHOR]

The paper discusses the formation and characteristics of stratified air–water downflow in the mesodomain. The stratified pattern, observed at low phase velocities, is characterized by air and water flowing side by side and both wetting the conduit wall, similar to stratified distributions in horizontal conduits. Such flow segregation without the influence of gravity is counterintuitive and no detailed investigation on the formation and flow physics of this distribution is reported till date. We have performed extensive experiments in glass conduits of 2.5–12.5 mm diameter where the two phases are introduced through T and Y junctions with different included angles between the entry arms. Our experiments reveal that stratified flows are formed up to a critical angle ϕ c subtended by the edges of the circumferential liquid film and beyond the critical wetting angle, the flow pattern is annular with liquid completely wetting the conduit wall. We further note ϕ c to depend on liquid properties, included angle of Y-entry, conduit diameter, and phase flow rates. Based on experimental observations, we propose a simplistic analysis to relate the liquid properties, conduit dimension, and Y-entry included angle and the liquid and gas flow rates to describe the formation of stratified and annular flow at the junction. The analysis also estimates the in situ void fraction during stratified gas–liquid downflow. [ABSTRACT FROM AUTHOR]

The mechanical and dielectric relaxation moduli of dendrimers with the excluded volume interactions are theoretically investigated within the framework of Rouse-Zimm theory. The excluded volume interactions in dendrimers are expressed in terms of the effective co-volume between nearest non-bonded monomers, modeled through the delta function pseudopotential. These short range interactions play a decisive role in determining the mechanical moduli of dendrimers. The characteristic feature of excluded volume effect in the mechanical moduli is typically revealed in the intermediate frequency regime, where dendrimers with varied strengths of excluded volume interactions display power-law scaling relations with frequency. The value of the power-law scaling exponents for the mechanical moduli exactly matches with the earlier results for dendrimers in good solvent conditions. The mechanical moduli are dominated by the smaller eigenvalues in the low frequency region corresponding to the collective modes with smaller relaxation rates, which increase with the corresponding increase of the excluded volume interactions. The local modes are practically independent of excluded volume. A cross-over between the loss and storage moduli is observed at the intermediate frequency regime. The position of this cross-over shifts towards the low frequency region with the decrease in the strength of the excluded volume, which resembles the behavior of dendrimers with the variation of temperature as reported in an earlier experimental work. The structure of dendrimers show a conspicuous change as a function of the effective co-volume between the nearest non-bonded monomers. The real part of dielectric relaxation moduli remains unchanged by varying excluded volume parameters, while its imaginary part varies with the change in strength of excluded volumes for the entire range of frequency except in the high frequency regime. A comparison with the model semiflexible dendrimers show that in such densely packed molecules the mechanical relaxation moduli are strongly affected by the short-ranged excluded volume interactions between the nearest non-bonded monomers. [ABSTRACT FROM AUTHOR]

Polypyrrole/carbon (PPy/C) composites have been synthesized using varying concentration of p-toluenesulfonate (pTS) dopant by surface initiated in-situ chemical oxidative polymerization. The synthesis and influence of pTS on the structure of the PPy/C composites are confirmed by Fourier transform infrared studies and the morphological features have been examined by scanning electron microscopy. X-ray photoelectron spectroscopy, employed to examine the surface composition and doping level of these composites, confirms the anionic doping into the polymer backbone. Electron spin resonance measurement has been carried out on these samples to identify the nature of the charge carriers and their concentration at different doping levels. The dc electrical conductivity of these composites has been measured in the temperature range ~10-305 K. The observed results have been analyzed in the framework of existing theoretical models. Different Mott's parameters, such as characteristic temperature (T0), density of states at the Fermi level {N(EF)}, average hopping distance (R), and average hopping energy (W), evaluated from dc conductivity data supports the applicability of Mott's three dimensional variable range hopping mechanism in this system. [ABSTRACT FROM AUTHOR]

The conformational and dynamic properties of semiflexible randomly hyperbranched polymers are investigated in dilute solutions within the framework of optimized Rouse-Zimm formalism. Semiflexibility is incorporated by restricting the directions and orientations of the respective bond vectors, while hydrodynamic interactions are modeled through the preaveraged Oseen tensor. The effect of semiflexibility is typically reflected in the intermediate frequency regime of the viscoelastic relaxation moduli where the bond orientation angle restores the characteristic power-law scaling in fractal structures, as in randomly hyperbranched polymers. Despite the absence of this power-law scaling regime in flexible randomly hyperbranched polymers and in earlier models of semiflexible randomly branched polymers due to weak disorder [C. von Ferber and A. Blumen, J. Chem. Phys. 116, 8616 (2002)], this power-law behavior may be reinstated by explicitly modeling hyperbranched polymers as a Vicsek fractals. The length of this power-law zone in the intermediate frequency region is a combined function of the number of monomers and the degree of semiflexibility. A clear conformational transition from compact to open structures is facilitated by changing the bond orientation angle, where the compressed conformations are compact, while the expanded ones are relatively non-compact. The extent of compactness in the compressed conformations are much less compared to the semiflexible dendrimers, which resemble hard spheres. The fractal dimensions of the compressed and expanded conformations calculated from the Porod's scaling law vary as a function of the bond orientation angle, spanning the entire range of three distinct scaling regimes of linear polymers in three-dimensions. The results confirm that semiflexibility exactly accounts for the excluded volume interactions which are expected to be significant for such polymers with complex topologies. [ABSTRACT FROM AUTHOR]

We theoretically investigate the conformational properties of semiflexible dendrimers where the semiflexibility is implemented by topologically restricting the bond directions and orientations of the respective bond vectors. Molecular size (radius of gyration, Rg and Wiener index, W), shape factor ρ, configurational free energy F, and the static structure factor, S(q) of semiflexible dendrimers are analyzed as a function of the bond orientation angle, [lowercase_phi_synonym]. The size of the lower generation dendrimers decreases with increasing [lowercase_phi_synonym] throughout the entire range of [lowercase_phi_synonym], [lowercase_phi_synonym] ∈ (0, π). The higher generation dendrimers show a non-uniform behavior, for compressed conformations the size decreases with increasing [lowercase_phi_synonym], while for the expanded ones it increases with the increase in [lowercase_phi_synonym]. A conformational transition occurs for the higher generation dendrimers from the limiting value of the hard sphere to an ideal chain with the change in [lowercase_phi_synonym]. This conformational transition at [lowercase_phi_synonym] = π/2 is also reflected in the configurational free energy. The configurational free energy exhibits a discontinuous behavior with the variation of [lowercase_phi_synonym], and this discontinuity occurs at [lowercase_phi_synonym] = π/2. However, no such conformational transition is observed with the variation of the bond direction angle, θ, generation, G and functionality, f of the semiflexible dendrimers. The flexible dendrimer, i.e., at [lowercase_phi_synonym] = π/2 is flanked between the compressed and expanded conformations of the semiflexible dendrimers resembling a hard sphere. The Kratky plot of the structure factor of all conformations quantitatively match with the results obtained from experiments and simulations in the low q-region in respect to the position of the major Kratky peak. For higher wave numbers, the Kratky plots for all conformations of semiflexible dendrimers agree with earlier theoretical results of model dendrimers [R. La Ferla, J. Chem. Phys. 106, 688 (1997); F. Ganazzoli, R. La Ferla, and G. Raffaini, Macromolecules 34, 4222 (2001)] but are in sharp contrast to the experimental [S. Rathgeber et al., J. Chem. Phys. 117, 4047 (2002); S. Rathgeber, T. Pakula, and V. Urban, J. Chem. Phys. 121, 3840 (2004)] and simulated [M. L. Mansfield and L. I. Klushin, Macromolecules 26, 4262 (1993)] scattering curves for the higher generation dendrimers. All compressed conformations (0 < [lowercase_phi_synonym] < π/2) behave as compact hard spheres, while the expanded conformations (π/2 < [lowercase_phi_synonym] < π) are relatively more open, partially decongesting the steric crowding among the monomers with increasing [lowercase_phi_synonym]. [ABSTRACT FROM AUTHOR]

Very recently, the discovery of ultra-tetragonal PbTiO3 thin films was reported [Zhang et al., Science, 361, 494 (2018)], in which the switchable out-of-plane polarization was seen to be almost twice that of any previously known ferroelectric. To understand more about this system and to explore features that might contribute to these remarkable functional properties, we have mapped the polarization microstructure on the nanoscale using piezoresponse force microscopy (PFM) (scan sizes less than 700 nm). Our study reveals an extremely fine-scale pattern, with individual domains typically 20–50 nm in size, all of which exhibit both out-of-plane and in-plane polarization components. In-plane vector PFM polarization maps show strongly charged quadrant-lattice domain arrays with fourfold domain wall junctions (vertices). The existence of fourfold vertices in ferroelectrics is rare but can be explained via the "Ashkin-Teller" model, in which very large interfacial lattice mismatch strains and local electric fields play a role. This ultra-tetragonal ferroelectric system was expected to contain straightforward c-axis out-of-plane 180° domains, but instead shows an extremely rich nanoscale domain tiling pattern; these unusual nanodomains may be important in facilitating the extremely high switchable polarization values previously reported. [ABSTRACT FROM AUTHOR]

The radially expanding twin (circular and vertical) liquid sheets produced by impingement of a vertical cylindrical liquid jet onto a horizontally placed cone-disk deflector with a single slot were examined experimentally in the present work. Dynamics of these liquid sheets and the events leading to their breakup were studied by carrying out high-speed shadowgraphy simultaneously from side, front, and top views at a 5.4 kHz framing rate and for the jet Weber number (Wejet) range of 993 < Wejet < 3776. In the presence of the slot, the variation of the radial breakup distance of the circular sheet (Rb,CS) with Wejet changed from the monotonically decreasing trend ( R b , C S ∼ W e j e t − 0.44 ) to a nonmonotonic increasing and decreasing one. Furthermore, Rb,CS was found to be lowered by about 42% compared to the breakup distance Rb,CS,no-slot of the circular sheet for the no-slot deflector. The vertical sheet breakup distance (Rb,Vs) was found to increase monotonically with the slot Weber number W e s l o t 0.44 . Three primary sources of droplet production, namely, the lower and front edges of the vertical sheet and the rim of the circular sheet, were identified. The smallest droplets were seen to originate from the front edge (D32,FE) and the largest droplets from the lower edge (D32,LE) of the vertical sheet. The measured droplet diameters followed D 32 , L E ∼ W e j e t − 1 / 3 and D 32 , F E ∼ W e j e t − 1 / 4 , whereas the droplets originating at the rim of the circular sheet followed D 32 , r i m ∼ W e j e t − 2 / 3 . The droplets at all three edges were found to depend more strongly on the ligament thickness than the ligament length. Following conservation of mass, a linear relation between the droplet diameter, D32, and the ligament thickness, tlig, at each edge has been obtained. [ABSTRACT FROM AUTHOR]

The conductive characteristics of Bi0.9La0.1Fe0.96Mg0.04O3 (BLFM) thin film are investigated at various temperatures and a negative differential resistance (NDR) is observed in the thin film, where a leakage current peak occurs upon application of a downward electric field above 80 °C. The origin of the NDR behavior is shown to be related to the ionic defect of oxygen vacancies (VO••) present in the film. On the basis of analyzing the leakage mechanism and surface potential behavior, the NDR behavior can be understood by considering the competition between the polarized distribution and neutralization of VO••. [ABSTRACT FROM AUTHOR]

The intramolecular relaxation dynamics of semiflexible dendrimers in dilute solutions are theoretically investigated in the framework of optimized Rouse-Zimm formalism. Semiflexibility is implemented by modeling topological restrictions on the bond directions and orientations of the respective bond-vectors. Based on our recently developed approach for semiflexible dendrimers [A. Kumar and P. Biswas, Macromolecules 43, 7378 (2010)], the mechanical and dielectric relaxation moduli are studied as functions of local flexibility parameters and branching topology. It is rather interesting to observe that semiflexibility affects the local modes of G′′(ω) and Δ[variant_greek_epsilon]′′(ω), which have lower relaxation rate with increasing bond restrictions, while the collective modes with small relaxation rate remain almost constant. The relaxation dynamics of the flexible dendrimer is similar to that of the semiflexible dendrimer with unrestricted bond orientations ([lowercase_phi_synonym] = 0) and is flanked by the compressed ([lowercase_phi_synonym] = 30°) and expanded ([lowercase_phi_synonym] = 150°) conformations, respectively. The effect of semiflexibility is typically reflected in the intermediate frequency regime. The expanded conformations of semiflexible dendrimers display a power-law behavior in the intermediate frequency regime for both loss and storage modulus resembling fractal structures, while the compressed and unrestricted bond orientation conformations exhibit an approximately logarithmic dependence. The power-law exponent is found to be similar to the flexible dendrimers with excluded volume interactions. Thus, by tuning [lowercase_phi_synonym], a spectrum of dynamic relaxation pattern is obtained spanning a broad range of conformations from a power-law fractal network to a non-fractal one. In certain limits, this highly generalized model captures the characteristics of flexible dendrimers and also resembles La Ferla's model semiflexible dendrimers. The influence of hydrodynamic interactions reduces the dynamical range and the width of the intermediate domain by decreasing the smaller relaxation rates and increasing the higher relaxation rates correspondingly. [ABSTRACT FROM AUTHOR]

Poly(2,5-dimethoxyaniline) (PDMA) has been synthesized by chemical oxidative polymerization technique using varying ratio of oxidants; ferric chloride (FeCl3) and ammonium persulfate [(NH4)2S2O8], in an inert atmosphere at low temperature ∼278 K. The synthesized samples of PDMA have been characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and by measuring its dc conductivity (σdc). The temperature dependence of dc conductivity of PDMA samples has been examined in the wide temperature range 6–303 K. The analysis of dc conductivity data reveals that in the temperature range ∼100–303 K, the dc conductivity is predominantly governed by Mott’s three-dimensional variable range hopping, however, below 100 K tunneling seems to dominate. Different Mott’s parameters such as characteristic temperature (T0), density of states at the Fermi level [N(EF)], the average hopping distance (R), and the average hopping energy (W) have been estimated for all the PDMA samples and are in good agreement with the values reported earlier for other conjugated polymers. [ABSTRACT FROM AUTHOR]

The magnetic properties of the nanoparticles of hexacyanometallate based molecular magnetic compound Fe[Fe(CN)6]·xH2O have been investigated using dc magnetization and the frequency dependent real part of ac susceptibility χac′ techniques. The magnetic properties of these nanoparticles with an average particle diameter ∼50 nm have been compared with that of the bulk polycrystalline sample. A reduction in the Curie temperature as well as low coercivity and remanent magnetization have been found for the nanoparticles compared to those for the bulk polycrystalline sample. The maximum magnetization for the nanoparticles is also found to be smaller as compared to that for the bulk polycrystalline sample. For the nanoparticles, the peak temperature Tp in the χac′ vs T curve has been found to shift to a higher temperature with increasing frequency and this frequency dependence is described well by a power law. The fitting yields the relaxation time constant τ0=1.3×10-13 s, the freezing temperature Tg=10.63 K, and the critical exponent zν=5.5±0.3. For the bulk polycrystalline sample, no such shift in the ac susceptibility peak temperature has been observed. The time dependence of the thermoremanent magnetization has been observed only for the nanoparticles, which could be represented well with a stretched exponential law. The observed magnetic behavior of the nanocrystalline sample indicates the presence of disordered spins (leading to a spin-glass behavior) in these ferromagnetically ordered particles. [ABSTRACT FROM AUTHOR]

This article reports on the formation and electronic characteristics of conducting carbon nanowires produced by swift heavy ion irradiation of a fullerene thin film. This study shows that it is possible to create arrays of carbon nanowires, which are perfectly parallel to each other and perpendicular to the substrate. As-deposited fullerene films exhibit poor field emission characteristics with breakdown fields as high as 51 V/μm, whereas low dose ion irradiated fullerene film produces a threshold field as low as 9 V/μm. The present approach of making conducting carbon nanowires by ion irradiation for potential field emitters and large area applications is also discussed. [ABSTRACT FROM AUTHOR]

Conducting nanowires parallel to each other, embedded in fullerene matrix are synthesized by high energy heavy ion irradiation of thin fullerene film at low fluence (up to 5×1011 ions/cm2). The conductivity of the conducting zone is about seven orders of magnitude higher than that of the fullerene matrix. The conducting nanowires are evidenced by conducting atomic force microscopy. The typical diameter of the conducting tracks is observed to be about 40–100 nm. The creation of conducting wires is explained by transformation of fullerene to conducting form of carbon in the ion track, surrounded by the polymerized zone. The polymerization of fullerene is evidenced by Fourier transform infrared spectroscopy. [ABSTRACT FROM AUTHOR]

The structural, magnetotransport, and angle-resolved photoemission spectroscopy (ARPES) of Ag-doped Bi2Se3 single crystals are presented. Temperature dependent resistivity exhibits metallic behavior with a slope change above 200 K for Ag-doped Bi2Se3. The magnetoresistance shows positive quadratic dependence at low fields satisfying Kohler's rule. Hall resistivity measurement shows that electrons are dominant charge carriers. Furthermore, these results agree well with the ARPES spectra observed at T = 20 K, where the Fermi level lies inside the bulk conduction band. The Dirac point of the topological surface states is shifted toward higher binding energy (∼0.12 eV) for Ag-doped samples as compared to pristine Bi2Se3. [ABSTRACT FROM AUTHOR]

One of the induced multiferroic materials, CuO has the magnetic as well as ferroelectric phase transition at same temperature (TN1∼213 K, TC and TN2∼230 K). These type of materials can show two types of entropy; magnetic field induced entropy (Magnetocaloric Effect) as well as electeric field induced entropy (Electrocaloric Effect). The presence of both type of entropy may be called "Multicaloric Entropy" (M. Vopson, Solid State Commun. 152, 2067 (2012) and Meng et al., Phys. Lett. A 377, 567 (2013)). We observed that "Multicaloric Entropy" in the induced multiferroic materials also depends on the magnetoelectric interaction (c). Therofore, this numerical attempt to calculate the entropy of CuO may be useful for the future "electromagnetic" based refrigerator technology. [ABSTRACT FROM AUTHOR]