Small Polaron Hopping Conduction Mechanism Research Articles

High temperature study of dielectric and electrical conduction behaviour of La2NiO4

Materials showing negative permittivity have attracted considerable attention from researchers on account of their notable applications in electronic and electromagnetic devices. Discovering materials exhibiting negative permittivity is a challenging task. Very few single-phase oxides have been reported as negative permittivity materials. In this work, we have attempted to investigate the dielectric properties of La2NiO4 to explore the possibility of negative permittivity. To achieve the goal, powder, and ceramic of La2NiO4 have been synthesized by the conventional solid-state reaction method. Rietveld refinement of the X-ray diffraction data studies has confirmed the tetragonal structure and space group I4/mmm. The Dielectric properties and AC conductivity have been studied in the frequency range of 20 Hz–2 MHz and over a wide temperature range (30 °C–600 °C). The permittivity of La2NiO4 is found to be negative at all the measured frequencies and temperatures. The Drude model fitted the experimental data very well, suggesting that negative permittivity behavior can be assigned to the plasma oscillation of conducting electrons. The trend of AC conductivity with frequency is similar to the skin effect observed in metals. The variation of DC conductivity with temperature indicated small polaron hopping conduction mechanism. Analysis of reactance (Z′′) suggested inductive electrical character in the tested frequency and temperature range. Room temperature negative permittivity behavior of La2NiO4 makes it a potential candidate for practical electronic and electromagnetic devices that work in the Radio-frequency range. Furthermore, this work will add a new member to the family of Perovskite oxides showing tunable negative permittivity.

Investigation of magnetic properties and colossal magnetoresistance in nanocrystalline doped manganite

Here in, we report structural, magnetic, and magneto-transport properties of nanocrystalline La0.6Ag0.2Bi0.2MnO3 prepared 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, ∼ 146 K. The complete investigation of isothermal magnetization (), 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) at upon 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.

Influence of the A-site cation on structural, morphological, magnetic, optical and transport properties of R2CoMnO6(R = Nd, Y, Ho and Er) double perovskite oxides

The A-site substituted double perovskite oxides (DPOs) have in the recent decades gained much attention due to their various interesting properties and possible applications. For this reason, R2CoMnO6 (R = Nd, Y, Ho, and Er) DPOs have been synthesized using the auto-combustion sol-gel method. X-ray diffraction analysis suggests the crystal structure, i.e., monoclinic for all under-investigated DPOs at room temperature (RT), consisting of space group P2 1 /n which is confirmed by Rietveld refinement. Crystallite size is calculated using Scherrer and Williamson-Hall methods, and it was found that the crystallite size decreased with decreasing ionic radii from 55–29 nm on average. The micrographs were obtained by using a field-emission scanning electron microscope (FE-SEM), which reveals an almost homogeneous distribution of grains throughout the surface of all DPOs. All observed infrared and Raman active phonon modes have been assigned to vibrations of atoms and groups of atoms consistent with the prediction of group theory. The intermediate band gap values (1.34–1.63 eV) determined by the Tauc relations suggest the semiconducting nature of these DPOs which makes them promising materials for photovoltaic applications. Dc electrical resistivity and dielectric measurements also suggest semiconducting behaviour above ambient temperature, which is attributed to a small polaron hopping conduction mechanism. The Maxwell-Wagner type interfacial polarization has described the nature of the frequency-dependent dielectric constants in these DPOs. The dielectric (ac) study also suggests the small polaron hopping conduction mechanism in all samples, which supports our findings in resistivity measurements.

Small polaron hopping conduction mechanism and enhanced thermoelectric power factor in the perovskite LaCoO3 ceramic.

Among the various thermoelectric oxide materials, perovskites offer more flexibility to adjust the interdependent thermoelectric parameters for an improved thermoelectric performance. In this work, we investigated the effect of A-site cation deficiency and Sr-substitution on the thermoelectric properties of the LaCoO3 ceramic synthesized via a solid-state reaction. A rhombohedral crystal structure with the R3̄c space group was revealed through Rietveld refinement of the XRD data. XPS analysis further confirmed the presence of multiple oxidation states of Co, and the mechanism of charge transport involving these multivalent cations was described using the small polaron hopping model. The La deficiency and Sr-substitution were found to increase the electrical conductivity in the LCO1 and LCO2 compositions, which resulted in a significant increase in the thermoelectric power factor. It was found that the increase in electrical conductivity of LCO1 and LCO2 was caused by a substantial reduction in the activation energy barrier for small polaron hopping conduction and an increase in fractional polaron concentration. The maximum power factor value of 78 μW m-1 K-2 was observed for the LCO2 composition at 403 K.

Dielectric capacitance and energy storage performances of organic molecule stabilized hexagonal lead iodide with a layered network

Nanostructured lead iodide particles were synthesized by applying a wet chemical synthesis route in presence of aminobenzene and fluoro-aminobenzene as ligands. The ligands were performed as the stabilizer of the particles. Two types of devices were designed using aminobenzene and fluoro-aminobenzene stabilized lead iodide. The dielectric capacitance, AC-conductivity, field-driven polarization and energy storage performances of the devices were investigated under varying temperature and frequency conditions. The electrical performance of fluoro-aminobenzene stabilized lead iodide-based device exhibited superior performance than that of aminobenzene-stabilized lead iodide-based devices. The fluoro-aminobenzene based device showed the maximum dielectric constant value 398 under the frequency of 100 Hz at 80 °C and maintained a low dielectric loss and high quality factor within the frequency range from 100 Hz to 2 kHz. Both the devices demonstrated the small polaron hopping conduction mechanism. The fluoro-aminobenzene based device maintained a fatigue-free unipolar hysteresis loop under 4 kV/mm with the maximum polarization value of 0.21 μC/cm2 and attended a stable charge and discharge energy density for the period of 103 cycles.

Study of structural properties and conduction mechanisms of La0.67Ca0.2Ba0.13Fe0.97Ti0.03O3 perovskite

In the present investigation, the La0.67Ca0.2Ba0.13Fe0.97Ti0.03O3 perovskite structure is prepared using the auto combustion method. The Rietveld refinement of the X-ray diffraction results indicates that the prepared compound crystallizes in the orthorhombic structure with the Pnma space group. Morphologic and elastic properties are analyzed using electron microscopy and Raman spectroscopy techniques. The nanoparticles size of the investigated perovskite structure was determined using TEM microscopy and the nanocrystallites values were obtained from XRD patterns. The Raman investigation confirms that the prepared compound reveals similar vibration modes compared to the reported modes of the LaFeO3 structure. The semi-conductor behavior of the prepared compound is explained based on the small polaron hopping conduction mechanism. The conductivity spectra are studied using the universal Jonscher power law. The dynamic region of the spectra confirms the activation of the non-overlapping small polaron tunneling and the correlated barrier hopping conduction processes. Impedance analysis confirms the important role of the grain boundary contribution to the electrical properties of the studied structure. Also, the electrical conduction and the relaxation phenomena are related to the same origin. Different physical parameters of this compound are determined, which can orient their use in specific applications.

Transition of charge transport phenomena from 3D to 1D hopping at low temperatures in polyaniline/graphene composites

Here, we present the charge transport properties of polyaniline/graphene composites prepared by a chemical oxidation method in the presence of four different loading concentrations (2, 4, 6, and 8 wt. %) of graphene. The synthesized materials are characterized for surface and chemical bonding analyses through field-emission scanning electron microscopy and Fourier transform infrared spectroscopy techniques, respectively. The change in the chemical structure of the prepared composites with graphene loading concentrations revealed the possible increment in electrical conductivity. The room-temperature dc conductivity of the prepared composites was found to increase from ∼22 to 217 S/cm with an increase in the loading concentration of graphene from 2 to 8 wt. %. The temperature-dependent electrical conduction behavior of the prepared samples is investigated under Mott's variable-range hopping conduction mechanism. It is found that all composite samples follow three-dimensional (3D) hopping in the higher temperature region (>44 K), which transforms into one-dimensional (1D) hopping at lower temperatures (<44 K). A decrease in hopping distance (1.07–0.96 nm) and an increase in density of states (3.20 × 1021–4.95 × 1021 cm−3 eV−1) in three dimensions with an increase in the graphene loading concentration from 2 to 8 wt. % suggest the requirement of lower hopping energy (61.3–55.5 meV) for conduction. The estimated hopping parameters also revealed a nonadiabatic small-polaron hopping conduction mechanism that is followed by the charge carriers in the present samples for both one- and three-dimensional variable range hoppings.

Dielectric relaxations and optical properties of Mn-doped ZnO nanoparticles

Nanoparticles (NPs) of pure zinc oxide (ZnO) and Zn1-xMnxO, where x = 0.01 and 0.05, were prepared using the co-precipitation method. The X-ray diffraction patterns revealed that both pure ZnO and Mn-doped ZnO NPs crystallize in hexagonal wurtzite. Different structure parameters are given. Other characterizations, such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, and FTIR, were used to test the studied samples. The dielectric and optical properties were performed and discussed in detail. It was found that the dielectric permittivity and the ac conductivity of pure ZnO NPs increased significantly when the Mn ions substituted the Zn ones. A small polaron hopping conduction mechanism is suggested for the investigated samples. Different optical parameters were calculated in this work. The outcome results are discussed and compared to similar materials.

High temperature Seebeck coefficient, small-polaron conduction and work function of LiMn1.5Ni0.5O4 thin films

We report on the high temperature Seebeck coefficient, conduction mechanism and room temperature work function of LiMn1.5Ni0.5O4 thin film prepared using the radio frequency sputtering technique. Cubic spinel LiMn1.5Ni0.5O4 thin film exhibits a room temperature average work function value of 4.94 eV. DC electrical conductivity exhibits a small-polaron hopping mechanism with the activation energy of 0.47 eV. The polaron radius, inverse localization length and the Debye temperature values of LiMn1.5Ni0.5O4 thin films are predicted using the variable range hopping model and Raman studies. The Seebeck coefficient and the power factor values for the LiMn1.5Ni0.5O4 thin film is seen to vary from −1000 to −600 μV K−1 and 0.09 to 0.5 μW mK−2, respectively, in the temperature range of 420 to 560 K. Electrical transport studies reveal the fact that the LiMn1.5Ni0.5O4 thin film posseses n type charge carriers with a high Seebeck coefficient, high power factor and small-polaron hopping conduction mechanism in the temperature range of 420–560 K.

Synthesis, structure, magnetic behavior and dielectric relaxation of the LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) oxide ceramic

This study is devoted to the investigation of the high dielectric constant causes in complex oxides with a structure of the K2NiF4 type. А new thermobaric treated ceramics on the basis conjugate LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) solid solutions was synthesized and the study their structure, microstructure, magnetic and dielectric properties was performed. It is shown that antiferromagnetic interactions coexist with ferromagnetic, which become dominant towards to low temperatures; the appearance of two types of magnetic interactions may be related to the presence of magnetic ions of different valences. Different values of the dielectric constants ε are observed in wide region of frequencies 10–107 ​Hz. In obtained at ambient pressure LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) ceramics the highest permittivity ε value is only 30–50 in the frequency range from 1 ​kHz to 1 ​MHz. After the samples treatment at 1273 ​K and P ​= ​4 ​GPa during 5 ​min ε increases to 5–102–103 ​at 293 ​К and independent of frequency in the range (102–106) Hz. At the temperature increase the permittivity as well increases and the ε value becomes ~106 at, approximately, f ​= ​100 ​Hz and T ​= ​750 ​K. An obvious change of samples microstructure and polyhedra structure anisotropy in LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) was observed after the thermobaric treatment. Described in this article performed dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure, microstructure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and small polaron hopping conduction mechanism.

Impact of A-site rare earth substitution on structural, magnetic, optical and transport properties of double perovskites

In the current research work R2CoMnO6 (R = La, Sm, Gd and Dy) double perovskites (DPOs) have been synthesized using auto combustion sol-gel method. Structural characterizations were carried out by X-ray diffraction technique and the analysis confirms the correct crystal structure by Rietveld refinement with a monoclinic symmetry (space group P21/n) in all DPOs. Crystallite size has been calculated by using Scherrer and Williamson-Hall (W-H) methods and found that the crystallite size with the decrease in ionic radius (RLn) decreases from 61.37–49.03 nm on average. The IR reflectivity spectrums fitted by the Lorentz oscillator model reveal that the given DPOs have a monoclinic structure and change of R-site also has ability to impact on the crystal structure. The optical band gap has been estimated in the range of 1.30–1.60 eV reflecting that the considered DPOs have potential to be used as light harvesting materials. The resistivity data of all DPOs depict semiconductor like behavior above room temperature and this behavior has been best described by small polaron hopping (SPH) conduction mechanism. Dielectric measurements exhibit usual dielectric dispersion, which is due to the Maxwell-Wagner-type interfacial polarization in all DPOs. AC conductivity measurement also suggests the conduction is due to SPH.

Effect of Yttrium doping on structural, optical and transport properties of La2NiMnO6

We have prepared a series of double perovskites La2−xYxNiMnO6 (x = 0.0, 0.5, 1.0, 1.5, 2.0 mol%) by sol-gel method. The structural, optical and transport properties of La2−xYxNiMnO6 have been characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) and ultra-violet (UV) visible spectroscopy at room temperature whereas dielectric and electrical properties are calibrated in the temperature range of 293–473 K. The structural properties are discussed by rietveld refinement (JANA software) which gives monoclinic structure with space group P21/n for all series. FT-IR measurements give IR spectra which are fitted by using Lorentz oscillator model, optical conductivity, oscillator strength and damping factors. UV-visible spectroscopy gives optical band gaps, indicating the semiconducting behavior of observed series. The transport characteristics of La2−xYxNiMnO6 have been found by dielectric and electrical measurements. The dielectric constant, tangent losses and ac conductivities as function of frequency and temperature have been discussed in detail. The activation energies are calculated by Arrhenius plot which inveterate the semiconducting nature of all samples. It has been further confirmed that there is small polaron hopping (SPH) conduction mechanism in all samples.

Structural and electrical transport properties of (La0.7-Y )Ca0.3MnO3 manganites

Abstract The effect of yttrium (Y) substitution at La-site on structural, microstructural and electrical transport properties of (La0.7-xYx)Ca0.3MnO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were investigated. Samples were prepared by conventional solid state reaction method and structural properties of the samples were obtained using the Rietveld refinement of X-ray diffraction data. X-ray diffraction patterns show orthorhombic distorted perovskite structures. Resistivity measurement results of the LaYCaMnO3 compounds show that metal–insulator transition temperature, TMI shifts to lower temperature while the resistivity increases by increasing Y3+ substitution. In the metallic region (T TMI), resistivity data were fitted to model of small polaron hopping conduction mechanism and the activation energy, Ea increased as Y substitutions increases.

Impact of crystal stacking sequence on electrical transport and dielectric properties of the nanocrystalline BaCo0.9Mn0.1O3-δ

We investigate the electrical transport and dielectric properties of the nanocrystalline BaCo0.9Mn0.1O3-δ under 2H- and 12H-type hexagonal phases. Temperature dependent electrical transport properties under 2H- and 12H-type phases show semiconducting-like behavior above the magnetic transition. The numerical value of electrical resistivity of the 12H-type phase at low temperature is 10-fold higher than the 2H-type counterpart, following the trend of structural stacking sequence. The 12H-type phase exhibits rarely known characteristics of ferromagnetic-insulator. The conduction mechanism under both phases is studied using variable range and small polaron hopping conduction mechanism. The 12H-phase shows large magnetoresistance (∼60%) under an application of 5 T of magnetic field at 50 K. The relation between magnetization and electrical resistivity around the magnetic ordering temperature is studied. The relation has been used to correlate the magnetic entropy change derived by magnetization and electrical resistivity measurements. Temperature dependence and magnetic field induced dielectric permittivity of the 2H- and 12H-type hexagonal phases is studied around the magnetic ordering temperature. Both phases exhibit dielectric suppression by magnetic ordering. The field dependence dielectric behavior shows magnetocapacitance value of ∼4% for 2H-phase and ∼94% for 12H-phase at their magnetic ordering temperature under external magnetic field of 5 T. The existence of intrinsic magneto-dielectric coupling is studied under the framework of Ginzburg-Landau theory for ferroelectromagnet. The origin of extrinsic magneto-dielectric contribution is justified using combinational effect of large negative magnetoresistance and Maxwell-Wagner effect. The magnetic and electrical transport properties of the nanocrystalline BaCo0.9Mn0.1O3-δ compound are also studied using density of states. Nanocrystalline BaCo0.9Mn0.1O3-δ sample shows novel magnetic field-induced effect on the magnetic, electric and dielectric properties around the same temperature window which could be utilized for multi-functional applications.

Impact of the Sr doping on structural and magnetic properties of nanocrystalline Ba1-xSrxCo0.9Mn0.1O3-δ (0 ≤ x ≤ 0.5)

Abstract We have investigated the impact of Sr-doping on physical properties of the nanocrystalline Ba1-xSrxCo0.9Mn0.1O3-δ (0 ≤ x ≤ 0.5) samples synthesized by using sol–gel method under different annealing temperature. The X-ray diffraction patterns of the nanocrystalline samples annealed at 900 °C show 2H-type hexagonal stacking sequence which consist of one-dimensional chain of face sharing octahedra. With increase in annealing temperature, samples crystallize in mixed 2H + 12H-hexagonal polytypes, exhibiting additional terminal sharing tetrahedra. The magneto-structural properties influenced by annealing temperature under different Sr-doping level have been elaborated using spin model projection and superparamagnetic cluster contribution. The inclusion of 12H-phase showed higher magnetic moment contribution compared with single 2H-phase. The studied nanocrystalline samples show semiconducting-like electrical transport properties. The phase dependent electrical transport properties of the nanocrystalline samples have been studied using variable range hopping and small polaron hopping conduction mechanism. The synthesized samples exhibit moderate negative magnetoresistance for a field change of 5 T in the vicinity of the magnetic ordering. The numerical value of magnetoresistance suppresses with increase in Sr-doping and it shows the 2H-type hexagonal phase dominance. The relation between magnetization and electrical resistivity around the magnetic ordering temperature is well explained using magnetoresistance data and magnetization isotherms.

Hole doping effect on structure, transport and magnetic properties of Dy1-xBaxMnO3 (0 ≤x ≤1)

Structural, electrical and magnetic properties of Dy1-xBaxMnO3 compounds synthesized by the standard solid state reaction route are reported in this paper. For x = 0.0 to 0.5, the compounds have orthorhombic structure and for x = 0.8 and 1.0, the structure changed to hexagonal structure corresponding to 2H. Raman spectra of the materials compliment structural phase transition. Phonon lifetimes estimated from the Raman line width were found to be in the order of pico seconds. X-ray photoelectron spectra of Dy1-xBaxMnO3, revealed the presence of Dy, Ba, Mn and O elements with respective binding energies. Mn ions were found to be in the mixed valent states of Mn (III) and Mn (IV) and their ratio decreased with increasing Ba concentration. Temperature behavior of electrical resistivity of all the compounds showed semiconducting behavior that persisted in the entire temperature range with small polaron hopping conduction mechanism. As Ba content increased, activation energies for hopping of polarons decreased in the orthorhombic phase and increased in the hexagonal phase. Magnetic studies as a function of temperature indicated that ordering temperatures of rare earth (Dy) moments are suppressed with Ba substitution. Random occupation of magnetic Dy3+, Mn3+ and Mn4+ ions in Dy1-xBaxMnO3 system resulted in complex magnetic structures. The reduction in the experimental effective magnetic moments determined from the Curie-Weiss fit parameters followed the magnetic dilution. Isothermal magnetization curves confirmed the presence of multiple interactions between the magnetic ions.

Ferroelectric, dielectric and electrical behavior of two-dimensional lead sulphide nanosheets

Two-dimensional pure cubic phase lead sulphide (PbS) nanosheets were synthesized using solid state reaction method at ambient pressure and low temperature ~190 °C. From 210 K–300 K, small polaron hopping conduction mechanism was found to be dominant in PbS nanosheets at frequencies 20 Hz–2 MHz. High values of dielectric constant (~200) and electrical conductivity (of the order of 10−3 S m−1 at 300 K) of PbS nanosheets were extracted suggesting that it is a proficient material for capacitive storage devices. A high value of density of states of the order of 1032 eV−1 cm−3 was obtained for PbS nanosheets. The capacitance-voltage (CV) measurements of PbS nanosheets resulted in a stable butterfly loop due to switching of ferroelectric polarization at 300 K. The permittivity calculated at 0 V capacitance was ~150 and the dielectric loss remained below ~0.50. The polarization-voltage (QV) measurements showed a remnant polarization 23 µC cm−2 in PbS nanosheets. The leakage current density was below 0.5 mA cm−2 in the range ±5 V.

Electronic conduction mechanism and defect chemical model of LaNi0.4Fe0.6O3 − δ

In order to elucidate the electronic conduction mechanism and defect chemical model of LaNi0.4Fe0.6O3−δ at high temperatures, electrical conductivity (σ), Seebeck coefficient (S), and oxygen vacancy concentration (δ) of LaNi0.4Fe0.6O3−δ were measured as a function of oxygen partial pressure (p(O2)) and temperature. Relatively large σ and small positive S values are observed, which indicates the contribution of ionic conduction is negligibly small to thermoelectric power and the major electronic carrier is a hole. From the analysis of σ and S, it is expected that the LaNi0.4Fe0.6O3−δ has small polaron hopping conduction mechanism where an electron is localized on the Fe. The slope of δ vs p(O2) shows a minimum value near the stoichiometric composition and the δ increases as p(O2) reduces and temperature increases. The relationship between δ vs. log p(O2) is analyzed by a localized electron model and the behavior of the oxygen nonstoichiometry of LaNi0.4Fe0.6O3−δ can be explained.

Dielectric properties and impedance analysis of polycrystalline Li-Si ferrite prepared by high energy ball milling technique

The effect of Si substitution on the ac electrical conductivity, dielectric and impedance properties of Li0.5+0.5xSixFe2.5−1.5xO4 (0≤x≤0.6) ferrite synthesized by high energy ball milling technique has been reported. The ac measurements were performed over a wide range of frequencies from 100Hz up to 1MHz and as a function of temperature from room temperature up to 960K. Ac electrical conductivity as a function of frequency and temperature exhibited a semiconducting behavior. Small polaron hopping conduction mechanism has been observed in all compositions. For the samples with x=0.0 and 0.1, the correlated barrier hopping mechanism was noticed at first, followed by the small polaron hopping conduction mechanism. The dielectric constant έ and dielectric loss ε″ decrease with increasing frequency and remain constant at higher frequencies, showing the usual dielectric dispersion. The dispersion of the dielectric properties was discussed through Koop’s phenomenological theory. The low dielectric loss tangent at higher frequencies makes the opportunity of these ferrites for high frequency applications. The impedance spectroscopy technique was utilized to investigate the effect of grain and grain boundary on the electrical properties of the present series.

Effects of Dy sub lattice dilution on transport and magnetic properties in Dy1-xKxMnO3

Interaction of multiple oxidation states of manganese ions with rare earth ions in manganites leads to the observation of various magnetic ground states. To understand the effect of average ionic size on electrical conductivity and magnetic ground state properties in Dy1-xKxMnO3 (x=0.0, 0.1, 0.2 & 0.3), we have investigated electron transport as a function of temperature and magnetic properties as a function of temperature, frequency and magnetic field of these compounds. Although mixed valent manganese ions can facilitate a double exchange interaction via oxygen ion leading to a ferromagnetic metallic ground state, no insulator-metal transition was detected. On the other hand, in the compounds with x=0.0 to 0.2, transport properties suggested an adiabatic small polaron hopping conduction mechanism. However, x=0.3 compound followed a variable range hopping conduction. Temperature variation of magnetization data exhibited three different types of transitions involving Mn and Dy ions. The bifurcation between zero field cooled and field cooled magnetization data was observed in all the compounds. Field-dependent magnetization of all the compounds showed hysteresis loops for temperatures less than 10 K. Although large irreversibility between zero field cooled and field cooled magnetization data was observed with a peak for x=0.3, the peak temperatures did not alter with frequency ruling out the possibility of spin glass behavior. The presence of hysteresis loops and lack of saturation magnetization implied the simultaneous presence of ferromagnetic and antiferromagnetic exchange interactions well within the antiferromagnetic ordering of Mn ions.