Search

Interfaces between metals and semiconducting materials can inevitably influence the magnetotransport properties, which are crucial for technological applications ranging from magnetic sensing to storage devices. By taking advantage of this, a metallic graphene foam is integrated with semiconducting copper-based metal sulfide nanocrystals, i.e., Cu2ZnSnS4 (copper-zinc-tin-sulfur) without direct chemical bonding and structural damage, which creates numerous nanoboundaries that can be basically used to tune the magnetotransport properties. Herein, the magnetoresistance of a graphene foam is enhanced from nearly 90 to 130% at room temperature and under the application of 5 T magnetic field strength due to the addition of Cu2ZnSnS4 nanocrystals in high densities. We believe that the enhancement of magnetoresistance in hybrid graphene foam/Cu2ZnSnS4 nanocrystals is due to the evolution of the mobility fluctuation mechanism, triggered by the formation of nanoboundaries. Incorporating Cu2ZnSnS4 nanocrystals into a graphene foam not only provides an effective way to further enhance the magnitude of magnetoresistance but also opens a suitable window to achieve efficient and highly functional magnetic sensors with a large, linear, and controllable response.

In this work, tetravalent Ti doping effect on structural, electrical, and magnetic properties of disordered Sm0.55Sr0.45Mn1- xTixO3 (0.0 ≤ x ≤ 0.2) system was investigated. Unlike the metallic nature of resistivity below Curie temperature TC in parent compound, the Ti-doped composition exhibits only semiconducting-type behavior throughout the measured temperature range. The electrical transport results above TC can be explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. Furthermore, magnetization measurements show drastic reduction of TC, Curie Weiss temperature (θCW) and effective magnetic moment (µeff) due to replacement of Ti4+ at Mn4+ site, which can broke exchange coupling of Mn3+/Mn4+ network, destroy the long-range ferromagnetic order.

Room temperature positive magnetoresistance (PMR) in graphene is a conventional phenomenon but we observed large negative magnetoresistance (NMR) in GF/polydimethylsiloxane (GF/PDMS) at room temperature for the first time. The largest NMR ~ 35% was detected at 250 K, while PMR is observed below 200 K. Furthermore, PMR at all temperatures is observed in regular GF specimens, hence, NMR is the result of the infiltration with the electrically insulating polymer. Forward interference and wavefunction shrinkage model has been employed to understand the transport mechanism in GF/PDMS. A critical temperature ~ 224 K for switching between NMR and PMR is observed at the crystallization temperature of PDMS, suggesting a change in polymer chain conformation may be a major reason leading to NMR in GF/PDMS specimens thus role of mechanical properties of PDMS in NMR cannot be ignored and observed locally via specially resolved atomic force microscopy. In addition, storage modulus and heat flow study shows similar transition temperature (~ 200 K) of NMR to PMR and provide an evidence of mechanical stable specimens. As is known, large, tunable, and unsaturated NMR at room temperature is very useful for future facile practical shapeable magnetoelectronic devices.

In the present paper we studied the structural, magnetotransport and thermopower properties of a series of polycrystalline La 0.7−x Sm x Ba 0.3 MnO 3 (0≤x≤0.2) compounds which were synthesized by conventional solid state reaction techniques. The Rietveld refinement of the X-ray diffraction pattern predicts the formation of single-phase compositions and doping of La 3+ by Sm 3+ ion converted the chemical structure form rhombohedral ( R-3C ) to orthorhombic ( Imma ) The scanning electron microscopy show clean smooth and densified structure images be a sign of good crystalline nature of the samples. The temperature dependent electrical resistivity is measured by standard four-probe method between 5 and 300 K exhibits Metal–Insulator Transition MIT which shows the decreasing trend with increasing Sm doping content and metallic state (T p2 ) that signifies importance of electron-electron, electron–phonon and electron-spin fluctuation scattering process. The metal–insulator transition temperature (T p2 ) is observed which decreases with the increase in doping content when magnetic field is applied. The resistivity data in high temperature region (T>T p2 ) are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The application of magnetic field suppresses the resistivity in entire temperature range and with increasing the Sm 3+ content the samples showed very high magnetoresistance. The thermoelectric power (S) of the reported samples exhibit a crossover from positive to negative value and it increases in doped samples. The analysis of thermoelectric power data confirms the applicability of the small polaron hopping model in high temperature region and in low temperature fitted to an equation containing diffusion, magnon drag, phonon drag and electron-spin fluctuation term. An appropriate justification for the observed behavior is specified.

We have synthesized a series of Sm 0.55 Sr 0.45−x Ag x MnO 3 (x = 0 & 0.15) by conventional solid state reaction method to scrutinize the effect of monovalent Ag + as a replacement of Sr 2+ ion on structural, electrical, magnetotransport and thermoelectric properties. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure having orthorhombic ( Pnma ) symmetry without any detectable impurity phase. It is observed that M ZFC and M FC curves become more manifested as Ag + content is increased which indicates an increase in magnetic frustration arising due to bending of Mn-O-Mn bond. The M-H plots show the narrow hysteresis loops which indicate the soft ferromagnetic nature. Magnetic studies also show that the Curie temperature T C is found to decrease with Ag + content. The metal–insulator transition temperature (T MI ) is observed which decreases with the increase of Ag + content when magnetic field is applied. The resistivity data in high temperature region are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The thermoelectric power (S) of the reported samples exhibits a crossover from positive to negative value and value of S increases in doped samples. The analysis of thermoelectric power data confirms that the small polaron hopping model in high temperature region and at low temperature electron–magnon scattering is the dominating in the FM region. With increasing the Ag + content the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR%) which make the compound more promising for scientific and technological applications.

Silver ions substituted samarium strontium manganite (Sm0.55Sr0.30Ag0.15MnO3) pervoskite was synthesized by using respective oxides in stoichiometric ratio through solid state reaction. The as-prepared sample was characterized by various analytical techniques to confirm its formation and understand the effect of monovalent silver ions in pervoskite lattice. X-ray diffraction pattern confirms the single phase formation while grain morphology in SEM image indicates good connectivity among the grains. The enhancement in metal to insulator transition temperature shows quenched disorder and magnetoresistance phenomena. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) emerge from grain growth factor and homogeneity induced by Ag+ ions in the lattice. The reduction in hysteresis loss resulted from antiferromagnetic - ferromagnetic (TN) and ferromagnetic - paramagnetic (Tc) transitions reveals the removal of disorder in perovskite lattice by Ag+ ions substitution. This increases the magnetic moment across distinct ions on the applying magnetic field. The rise in MR% (~99%) with silver doping emerging from smooth spin tunneling of the grains across the boundary and suppression of the disordered magnetic fluctuations with increase in magnetic field has been reported. The present compound exhibits the first order nature of magnetism and observed first time the highest value of TCR ~ 95%.

Polycrystalline yttrium barium cobaltite (YBaCo4O7) powdered sample was prepared by conventional solid state reaction route using high purity yttrium oxide, barium carbonate and cobalt oxide. The as-prepared sample was characterized by XRD diffraction, SEM/EDAX, Raman analytical techniques, resistivity and magnetization measurements for structural, morphological, electrical and magnetic properties assessment. XRD pattern confirms the single phase formation of the sample without any impurity. SEM image shows the hexagonal growth of the crystal and EDAX spectrum reveals stoichiometric composition of as prepared sample. The variation in electrical resistivity from 90 K to 300 K follows the variable range hopping conductivity mechanism. The strong broad overlapped Raman peaks of Co–O and Y–O stretching and bending vibrations of tetrahedral CoO4 with included components of YO6 of octahedral symmetry are obtained at 542 cm−1, 486 cm−1 and 636 cm−1, 436 cm−1, respectively. DC magnetic susceptibility exhibits very weak ferromagnetism below 80 K and does not obey Curie-Weiss law.

(ZnO/SnO2) thick films were fabricated using a low cost simplified screen printing technique on glass substrates.The optical properties of the deposited films were characterized in order to study its reflectance and to calculate the optical constants such as refractive index (n) and extinction coefficient (k) with respect to photon energy.The room temperature photoluminescence spectra of (ZnO/SnO2) nanocomposite shows strong emission peak at 389 nm and stretching at 512 nm with appearance of multi peaks at an excitation wavelength of 225 nm. Raman spectra shows existence of high and low vibrational phonon modes with presence of second ordered modes occur dues defects. Whereas SEM micrograph shows porous surface with no crackes.

The polycrystalline samples with nominal composition Eu0.5Sr0.5Mn1−x Cr x O3 (0 ≤ x ≤ 0.1) were prepared by the conventional solid state reaction method and characterized by X-ray diffraction, scanning electron microscopy and electrical resistivity behavior without and with magnetic field. The structural parameters obtained by using Rietveld refinement of X-ray diffraction data showed that all samples crystallize with orthorhombic perovskite type symmetry with Pbnm space group. The scanning electron micrograph images reveal that the increase in Cr substitution hinders grain growth and grain connectivity. The temperature dependence of electrical resistivity show the semiconducting nature of these compounds and support the small polaron hoping model and variable range hopping conduction model. The calculated hopping distance and activation energy decreased as rate of Cr content increased whereas density of states at Fermi level increased. A large negative magnetoresistance is also present in the sample at the lowest temperature of measurements.

We have synthesized the single phase polycrystalline sample of silver doped disordered Sm0.55Sr0.45−xAgxMnO3 using the conventional solid state method. They have been investigated by X-ray diffraction for phase evolution and their Rietveld refined X-ray diffraction pattern indicates an increase in lattice parameters and unit cell volume with Ag doping. The magnetization analysis shows the presence of a first order paramagnetic to ferromagnetic transition; the transition temperature and amount of thermal hysteresis decreases on Ag doping. The transport, magneto-transport results indicates decrease in metal to insulator transition, drastic increase in resistance and temperature coefficient of resistance (TCR %) with nearly unaffected colossal magnetoresistance effect which indicates that at least a part of silver is incorporated in the lattice. Scanning electron micrographs indicate that silver has also increased the grain growth sharpness and thus decrease the effect of grain boundary scattering. The significant value of TCR of ∼43% of our samples indicates their applied nature for bolometric application.

The Single phase Ho1-xGdxMnO3 (0 ≤ x ≤ 0.1) compounds were synthesized by solid-state reaction techniques and characterized with various techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, ferroelectric loop tracer. The Rietveld refined X-ray diffraction and Raman patterns indicate that all the compounds exhibit a single-phase hexagonal structure with a P63cm space group. The room temperature Raman spectra signify that the phonon peaks observed in all reported samples, slightly shift towards the lower temperatures. Moreover, an increase in the polarization values and reduction of leaky nature with increment in Gd concentration has been observed. The improved ferroelectric parameter obtained in our study is an advancement in the present understanding of multiferroic compounds.

We have synthesized Pr0.67Sr0.33−xAgxMnO3 (0 ≤ x ≤ 0.1) compound by conventional solid state reaction method at different sintering temperature. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure with orthorhombic (Pnma) symmetry without any detectable impurity phase. The grain growth and grain connectivity extensively improved at higher sintering temperature with doping concentration. Depending upon the doping and the increment of sintering temperature, the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR). An improvement in magneto-resistance and TCR with increasing the sintering temperature i.e., 1200–1300 °C which make the compound more promising for scientific and technological applications.

We have synthesized and investigated the effect of Ag doping in Pr0.67Sr1−xAgxMnO3 (0≤x≤0.3) perovskite materials via solid state reaction route. The structural, transport and magnetoresistance behavior have been studied. The Rietveld refinement of X-ray diffraction data shows that the compounds crystallize in an orthorhombic structure with Pnma space group with systematic non-linear variation in unit cell volume and lattice parameters. The grain morphology confirms that silver enhances conducting channels and reacts well with the compound only upto a certain doping level. The temperature dependent zero-field and in-field resistivity have been measured between 5 K and 300 K. The samples exhibit a systematic variation in metal to insulator transition temperature and a large magnetoresistance at x=0.10. The highest value of temperature coefficient of resistance has been observed by us for the first time. The results revealed that Ag takes part in the reaction only when the doping amount is small and at higher doping the system becomes a two phase composite.

A systematic series of polycrystalline compounds of YBaCo4−xNixO7 (0 ≤ x ≤ 0.3) have been synthesized by conventional solid-state reaction technique in order to scrutinize comprehensively the effect of Ni substitution on structural, micro-structural and electrical transport properties. X-ray diffraction patterns recorded at room temperature illustrate the structural phase transition with Ni from hexagonal (P6 3 mc) phase symmetry to trigonal (P31c) phase symmetry. The grain morphology observed via scanning electron microscopy indicates the decrease in grain size with increasing Ni percentage. The EDS analysis indicates that Ni is distributed randomly on Co sites also supports the change in crystal structure. The calculated electrical resistivity revealed the semiconducting nature of all compound with and without magnetic field. The resistivity data supported by using Mott’s variable range hopping (VRH) model to calculate the hopping distance (Rh), hopping energy (Eh) and density of states at Fermi level N(EF). Moreover, resistivity data are well fitted with small polaron hopping (SPH) model to investigate the conduction behaviour in the system. Thus, conduction mechanism carried out electronically induced structural phase changes involves in Ni–O–Ni and Ni–O–Co bond angles and bond lengths.

We have investigated the transport studies of the Nb-doped Pr0.7Sr0.3Mn1−xNbxO3 (0≤x≤0.05) manganites for the first time for identifying the transport properties as a function of the composition and temperature. Pr0.7Sr0.3Mn1−xNbxO3 (0≤x≤0.05) samples exhibit a single phase nature with an orthorhombic structure and a Pbnm space group. These materials show colossal magnetoresistance effect (CMR) and have wide technological applications such as magnetic sensors, reading head devices, spintronics, bolometers, magnetic refrigeration, etc. The computed transport properties such as cohesive energy, Reststrahlen frequency, Debye temperature, Gruneisen parameter and temperature dependence of specific heat of Pr0.7Sr0.3Mn1−xNbxO3 (0≤x≤0.05) manganites are discussed in detail in the present work by applying extended rigid ion model (ERIM) and have shown significant agreement with the corresponding available results.

The effect of strontium (Sr) doping on the structural, magnetic, electrical, and thermal properties of Pr1-xSrxCoO3 (0.1 ≤ x ≤ 0.5) has been studied. The samples were synthesized by using the conventional solid-state reaction method. The Rietveld refinement of X-ray diffraction patterns confirms the single-phase composition with orthorhombic (Pbnm) perovskite symmetry. The magnetization measurements revealed the paramagnetic to ferromagnetic transition and the transition temperature (Tc) increased with increasing Sr doping. The effective magnetic moments determined by the Curie-Weiss law show an increase in the Sr concentration. The temperature dependence of electrical resistivity suppressed with increasing the Sr content. Moreover, all the compounds other than x = 0.5 show the semiconducting nature. All semiconductor compositions (x = 0.1, 0.2, 0.3, and 0.4) in the high temperature region can be explained within the framework of the small polaron hopping model and the variable range hopping model, wherea...

A systematic study of polycrystalline sample with composition Eu0.5Sr0.5Mn0.9Cr0.1O3 has been undertaken and synthesized by conventional solid state reaction techniques. The room temperature XRD study reveals the single phase formation of the reported compound with orthorhombic structure having Pbnm space group. The temperature dependent resistivity study indicates the highly resistive nature of the compound especially in the low temperature region exhibits a semiconductor behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the temperature scale T* ∼ 9.05×106 K and finally the density of state at Fermi level N(EF) is calculated to be ∼ 61.63 × 1018 eV−1 cm−3.

In this paper, we report the enhancement of metal – insulator transition temperature (TMI) induced by magnetic field confirms the MR phenomenon. The polycrystalline Sm0.55Sr0.45MnO3 were synthesized using solid state reaction route. The XRD patterns using Full Prof Rietveld analysis shows that the sample has single phase nature without any detectable impurity. The SEM micrograph carried to observe the grain morphology and four probe resistivity measurements using with superconducting magnet to investigate the electrical behaviour. The sharp value of temperature coefficient of resistance (TCR) of 11% is used for infrared bolometric sensors.

We have synthesized and investigated the effect of Ag doping at x = 0 and 0.10 in Pr0.67Sr1−xAgxMnO3 via solid state reaction route. The Rietveld refinement of XRD data shows that these compounds crystallize in an orthorhombic structure with Pnma space group. On increasing the Ag content to x = 0.10, a linear variation in unit cell volume and lattice parameters is observed. The temperature dependent zero-field and in-field resistivity has been measured between 5 K to 300 K. The samples show a systematic variation in metal to insulator transition temperature and a large magnetoresistance (MR) is also observed with maxima at TMI. The highest value of Temperature Coefficient of Resistance (TCR) % has been observed by us for the first time.

The thermophysical properties such as structural, transport and elastic properties of the orthorhombic perovskite-type titanate system, LaTiO3 have been explored in detail for the first time by applying extended rigid ion model (ERIM). LaTiO3 has been subject of recent interest because of the variety of attractive behaviors, including a metal-insulator transition, spin-charge-orbital ordering and high-temperature superconductivity. LaTiO3 has been suggested to have promising scientific and technological applications. The theoretically computed thermophysical properties of LaTiO3 compound are in good agreement with the available results.