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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.

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 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.

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.