Nature of small-polaron hopping conduction and the effect of Cr doping on the transport properties of rare-earth manganite La0.5Pb0.5Mn1−xCrxO3

Study of the correlation between the magnetic and electrical properties of the La0.6Sr0.4MnO3 compound

In this work, we investigated the relationship between the electrical and magnetic properties of the superparamagnetic (SPM) La0.6Sr0.4MnO3 (S1C0) compound prepared by the sol-gel method. The (S1C0) sample displayed a ferromagnetic metallic (FMM) behavior at low temperatures and a paramagnetic semiconductor (PMSC) behavior at high temperatures. The FMM behavior was described by the Zener Double Exchange (ZDE) polynomial law containing the contributions of the electron-electron (e-e) interactions and the electron-magnon (e-m) scattering. The PMSC behavior was described by the Mott Variable Range Hopping (Mott-VRH) transport model. The semiconductor/metallic transition temperature has been approximated at the blocking temperature. The Thermal Coefficient of Resistivity (TCR), which exhibits a linear variation around ambient temperature, can be used as a calibration curve for thermometry. Thus, our sample can be considered as a good candidate for the detection of infrared radiation used in night vision bolometer technologies.

Magneto-transport and thermoelectric studies of antiperovskite semimetal: Mn3SnC

We explore the magnetotransport and thermoelectric (Seebeck and Nernst coefficients) properties of Mn3SnC, an antiperovskite magnetic Nodal line semimetal. Mn3SnC shows paramagnetic (PM) to concurrent antiferromagnetic (AFM)/ferromagnetic (FM) transition atT∼ 286 K. The electrical resistivity and Seebeck coefficient indicate the importance of electron-magnon scattering in the concurrent AFM/FM regime. We observed a large positive magnetoresistance (MR) of ∼8.2 at 8 T field near magnetic transition, in the otherwise negative MR behaviour for low temperatures. The electrical resistivity and MR show a weak thermal hysteresis around the boundary of transition temperature and the width of hysteresis decreases as magnetic field increases. Interestingly the Hall and Seebeck coefficients change sign from positive to negative below the transition temperature, highlighting the different scattering for holes and electrons in this multi-band system. The Seebeck and Nernst signal exhibit two sharp anomalies; one at the transition temperature and another at ∼50 K. The anomaly at magnetic transition in the Nernst signal disappear at 8 T magnetic field, owing to the reduction of magnetic fluctuation. A pseudo-gap near the Fermi level produces an upturn with a broad minimum in the Seebeck signal.

Investigation of magnetic properties and colossal magnetoresistance in nanocrystalline doped manganite

Here in, we report structural, magnetic, and magneto-transport properties of nanocrystalline La0.6Ag0.2Bi0.2MnO3prepared using citrate sol-gel method. By using scanning and transmission electron microscopy measurements, the morphology and particle size of the sample have been confirmed. The Mn2p x-ray photoelectron spectroscopy spectra revealed the nanoparticles contained the coexistence of Mn3+and Mn4+ions with Mn3+/Mn4+ratio of 2:1. Field-cooled and zero field-cooled magnetization protocols with temperature span of 5 K-300 K, confirm the paramagnetic (PM) to ferromagnetic (FM) phase transition at critical temperature,TC∼ 146 K. The complete investigation of isothermal magnetization (130⩽T (K)⩽160,ΔT=2 K), Arrott plots, and magnetocaloric effect as well as quantitative analysis of second-order phase transition has been studied. The criticality at the PM-FM transition was examined for the sample, and the obtained critical exponents were verified for their reliability through the utilization of the scaling hypothesis and Kouvel-Fisher plot. We observed a large magnetic entropy change (∼7 J-Kg-1K-1) atTCupon 5 T magnetic field strength. The renormalized magnetic entropy change plots are found to collapse onto a single curve, thus verifying the universality of the sample. Above the metal-insulator transitions the electrical resistivity shows a small polaron hopping conduction mechanism, however, at low temperatures scattering mechanism dominates and the whole range was explained by the universal percolation model. The colossal value of negative MR is found to be 88% at 168 K under an applied field strength of 2 T. As a result of our experimental data, we can grasp the intuitive understanding of magnetic as well as transport properties in Bi-doped manganite systems potential for magnetic sensors and spintronics applications.

Investigation of the structural, electrical, and dielectric properties of La0.5Sm0.2Sr0.3Mn1-x Cr x O3 for electrical application

In the present research, polycrystalline samples of La_0.5Sm_0.2Sr_0.3Mn_1−xCr_xO₃ are prepared using the self-combustion method. Then, we have studied their crystalline structure, and dielectric and electrical properties. The X-ray diffraction study shows that all the samples exhibit a single phase with orthorhombic structure (space group Pnma). The studied samples were also characterized by complex impedance spectroscopy in a wide range of temperatures and frequency. AC conductivity analyses are used to study the transport property of the investigated samples. These analyses indicate that the conduction mechanism is strongly dependent on temperature and frequency. It is also found that the conductivity decreases with Cr concentration. Complex impedance analysis confirms the contributions of grain and grain boundaries in the conduction mechanism. Finally, the impedance spectra, characterized by the appearance of semicircle arcs at different temperatures, were well modeled in terms of equivalent electrical circuits to explain the impedance results.

In the present research, polycrystalline samples of La_0.5Sm_0.2Sr_0.3Mn_1−xCr_xO₃ are prepared using the self-combustion method.

Spin-polarized tunneling and polaronic transport properties of polycrystalline (Sm1-yGdy)0.55Sr0.45MnO3(y= 0.5 and 0.7) compounds

The detail investigations on the magneto-transport properties of the polycrystalline (Sm_0.3Gd_0.7)_0.55Sr_0.45MnO₃(SGSMO-1) and (Sm_0.5Gd_0.5)_0.55Sr_0.45MnO₃(SGSMO-2) compounds, having a glassy-like and ferromagnetic ground states respectively have been carried out in details. Due to the existence of two different magnetic ground states in the above mentioned systems, the magneto-transport properties are markedly differed from each other, specially at the low temperature region. The highly semi-conducting nature of the SGSMO-1 compound is suppressed with the application of magnetic field, whereas the SGSMO-2 compound exhibits a metal-insulator transition in its pristine state. The high-temperature semiconducting state of both the systems can be well-explained with the polaronic transport mechanisms via small-polaron hopping and variable-range-hopping models. The low-temperature metallic states for both the systems are explored by considering the various contributions arise from the grain boundary effect, electron-electron, electron-phonon, electron-magnon etc scattering processes. The spin-polarized tunneling transport mechanism at the grain boundaries plays a crucial role in the enhancement of low-field magnetoresistance in the studied systems.

Non-overlapping small polaron tunneling conduction coupled dielectric relaxation in weak ferromagnetic NiAl2O4

The inverse spinel nickel aluminate micro-particles was successfully synthesized via solid-state synthesis techniques. The single phase cubic structure with space group Fd3m of the as-prepared sample was entrenched from Rietveld refinement of x-ray diffraction pattern. In addition, the photoluminescence (PL) and FTIR spectra were also performed to give strong evidence of its pure phase formation. The narrow hysteresis m-h loop and UV-DRS spectra at room temperature demonstrate its weak ferromagnetic and semiconducting nature with saturation magnetization 64.96  ×  10^-3 emu gm^-1 and direct optical band gap 2.03 eV respectively. The high-resolution FESEM micrographs and EDS elemental analysis exhibit its grain growth in µm range (217 µm) and presence of elemental compound Ni, Al and O respectively. The electrical transport properties were accomplished by complex impedance spectroscopy as a function of frequency (100 Hz-1 MHz) with the evolution of high temperature (300 °C-500 °C). The Nyquist plots (Z″ versus Z') were well fitted with an equivalent circuit model (QR) (QR) consisting of a series combination of intra and inter-granular contribution. Furthermore, the imaginary modulus spectra were also fitted with Kohlrausch-Williams-Watts (KWW) function, which represents two thermally activated peaks of grain and grain boundary effects. The low-frequency dispersive ac conductivity was elucidated using the following equation: [Formula: see text]. The increasing nature of temperature dependent frequency exponent (n) suggests the quantum mechanical tunneling: non-overlapping small polaron tunneling (NSPT) concept for conduction mechanism. In low-frequency region, the lattice and charge carrier polarization simultaneously contribute in dielectric permittivity.

Complex impedance, dielectric properties and electrical conduction mechanism of La0.5Ba0.5FeO3−δ perovskite oxides

The new perovskite compound La_0.5Ba_0.5FeO_3−δ was prepared by the sol–gel method.

Structural, magnetic, magneto-transport properties and Bean–Rodbell model simulation of disorder effects in Cr3+ substituted La0.67Ba0.33MnO3 nanocrystalline synthesized by modified Pechini method

Nanocrystalline powders (around 100 nm) of La_0.67Ba_0.33Cr_xMn_1−xO₃ (x ≤ 0.17) perovskites have been synthesized by the sol–gel based Pechini method at low temperatures.

Electrical transport and giant magnetoresistance in La0.75Sr0.25Mn1-xCrxO3 (0.15, 0.20 and 0.25) manganite oxide

We have investigated the influence of chromium (Cr) doping on the magneto-electrical properties of polycrystalline samples La0.75Sr0.25Mn1-xCrxO3 (0.15 ≤ x ≤ 0.25), prepared by the sol-gel method. Comparison of experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behavior of the three samples is quite well described by a theory based on electron-electron, electron-phonon and electron-magnon scattering and Kondo-like spin dependent scattering. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping (SPH) model is found to fit well the experimental curves.

Thermoelectric Seebeck effect in oxide-based resistive switching memory

Reversible resistive switching induced by an electric field in oxide-based resistive switching memory shows a promising application in future information storage and processing. It is believed that there are some local conductive filaments formed and ruptured in the resistive switching process. However, as a fundamental question, how electron transports in the formed conductive filament is still under debate due to the difficulty to directly characterize its physical and electrical properties. Here we investigate the intrinsic electronic transport mechanism in such conductive filament by measuring thermoelectric Seebeck effects. We show that the small-polaron hopping model can well describe the electronic transport process for all resistance states, although the corresponding temperature-dependent resistance behaviours are contrary. Moreover, at low resistance states, we observe a clear semiconductor-metal transition around 150 K. These results provide insight in understanding resistive switching process and establish a basic framework for modelling resistive switching behaviour.