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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.

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 this paper, CuInS2@ZnS (CIS@ZnS) core-shell quantum dots (QDs) were applied for the detection of heavy metals and bioanalytes. These Glutathione (GSH) capped CIS@ZnS QDs with an average size of 3.8 nm were treated using different biologically important biomolecule analytes, such as ascorbic acid (AA), citric acid (CA), oxalic acid (OA), cholesterol (Ch), cysteine (Cy), dextrose (Dx) and urea (U). According to spectroscopic analysis, the addition of cholesterol showed photoluminescence (PL) spectra of QDs remains unchanged at the main peak position 600 nm but generates a new peak at 487 nm with cholesterol dependent enhancement. Furthermore, the addition of citric acid contributes to PL quenching in the core-shell QDs without any spectral shift. Likewise, the interaction of CIS@ZnS QDs with different physiologically important heavy metal ions (HMI) was systematically studied as a luminescence probe. It was found out that the PL emission of CIS@ZnS QDs was effectively quenched by copper (Cu2+) ion with significant spectral shift detected. However, Hg2+ ions also lead to PL quenching at nanomolar level but with no spectral shift observed. According to these results, CIS@ZnS QDs are selectively sensitive to cholesterol, citric acid, Cu2+ and Hg2+ ions with satisfactory detection limit at nM level.

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.

Herein, we propose a quantum dots (QDs) based spectroscopic sensor for determination of ascorbic acid, gallic acid and oxalic acid. These aqueous stable AgInS2 (AIS) and AIS@ZnS QDs having average sizes of 2.5 ± 0.5 and 3.4 ± 0.5 nm, respectively, were surface coated with Glutathione (GSH), which provided enhanced stability against the aggregation/oxidation. These glutathione (GSH) capped AIS and AIS@ZnS core-shell nanostructures were systematically studied as a luminescence probe for the sensing of routinely used analytes. AIS QDs exhibit better specificity and selectivity for ascorbic acid and gallic acid detection, whereas, core-shell QDs show higher binding affinity and sensing ability for oxalic acid. It was noticed that AIS QDs exhibited 80% quenching efficiency towards gallic acid, compared to 55% of AIS@ZnS QDs. In addition, AIS QDs shows threefold increment in binding affinity towards gallic acid compared to AIS@ZnS nanostructures. As the consequence, AIS and AIS@ZnS QDs show concentration dependent red-shifted after binding with analytes. Based on this, AIS@ZnS QDs was found highly sensitive for the detection of oxalic acid with excellent detection limit as 35 nM. Interestingly, AIS QDs shows the specific and selective binding towards gallic acid where fluorescence quenching was noted and ascorbic acid for which fluorescence enhancement was observed. It was noted that these QDs shows the detection limit as 20 nM for GA and 45 nM for AA. Based on this, AIS and AIS@ZnS QDs can be used as fluorescence tool for multimode sensing of gallic acid ascorbic acid and oxalic acid with high selectivity and sensitivity.

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.

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...