Observation Of Hysteresis Loops Research Articles

Thermo‐Optical Bistability Enabled by Bound States in The Continuum in Silicon Metasurfaces

AbstractThe control of light through all‐optical means is a fundamental challenge in nanophotonics and a key effect in optical switching and logic. The optical bistability effect enables this control and can be observed in various planar photonic systems such as microdisk and photonic crystal cavities and waveguides. However, the recent advancements in flat optics with wavelength‐thin optical elements require nonlinear elements based on metastructures and metasurfaces. The performance of these systems can be enhanced with high‐Q bound states in the continuum (BIC), which leads to intense harmonic generation, improved light‐matter coupling, and pushes forward sensing limits. This study reports enhanced thermo‐optical nonlinearity and the observation of optical bistability in an all‐dielectric metasurface membrane with BIC. Unlike many other nanophotonic platforms, metasurfaces allow for fine control of the quality factor of the BIC resonance by managing the radiative losses. This provides an opportunity to control the parameters of the observed hysteresis loop and even switch from bistability to optical discrimination by varying the angle of incidence. Additionally, this work proposes a mechanism of nonlinear critical coupling that establishes the conditions for maximal hysteresis width and minimal switching power, which has not been reported before. The study suggests that all‐dielectric metasurfaces supporting BICs can serve as a flat‐optics platform for optical switching and modulation based on strong thermo‐optical nonlinearity.

Ferroelectric domain structure in Bi4Ti3O12 ceramics: Insights from Confocal Raman Microscopy

Bismuth Layer-Structured Ferroelectric (BLSF) materials with Bi4Ti3O12 composition exhibit high ferroelectricity, potential for high-temperature piezoelectricity, and the puzzle of low polarizability, explored via textured ceramics and domain configurations. Here, we show that a distinctive stripe configuration of 90° domains emerges for large platelet-like grains, while the smallest grains, possessing a more equiaxial morphology, exhibit a needle-like domain structure that significantly impacts the ferroelectric properties of the ceramics. The observed hysteresis loops suggest that polarization is effectively clamped, owing to reduced mobility along the needle-like domain walls, thereby leading to a reduction in remnant polarization as grain size diminishes. It is elucidated that the domain structure is intricately linked to both internal stress within the grains and the presence of defects, notably oxygen vacancies, at the domain walls. Consequently, these multifaceted factors are identified as key determinants of the ferroelectric activity within ceramics bearing such a distinctive crystalline structure.

Shear thickening and hysteresis in dense suspensions: The effect of particle shape

The flow of dense suspension of non-Brownian particles has been considered by various studies affected by their significance in a variety of industries and natural phenomena. In this study, we investigate the effect of polyhedron morphology on shear thickening, shear jamming, and hysteresis characteristics of non-Brownian suspension of acrylate particles. Particles with the same chemical nature and three different shapes of spherical (aspect ratio Γ = 1), elliptical paraboloid (Γ ≈ 1), and boat-shaped (Γ ≈ 3) are fabricated via photopolymerization-based methods. Studied suspensions show the shear-thinning behavior at low shear stresses and shear thickening behavior at the higher range of shear stress. Also, the strength of observed shear thickening is enhanced for the suspensions of polyhedron particles, which can be attributed to the heightened degree of interparticle frictional contacts. Furthermore, it is found that angularity not only shifts the predicted frictionless and frictional jamming packing fractions to lower values but also expands the shear jamming packing fraction range. Finally, a history-dependent hysteresis is observed in all samples due to the different particle spatial structures forming in ascending and descending flow modes. The observed hysteresis loops strongly depend on the volume fraction and diminish near the jamming packing fraction due to the restricted mobility space of particles. In addition, the tumbling of elongated particles also can decrease the hysteresis loop by enhancing viscosity in the ascending flow mode, where the structures are not fully developed.

On the thixotropy of mature fine tailings

The rheological behavior of mature fine tailings (MFTs) is investigated using transient and steady shear flow fields. The structure breakdown of intact MFT samples is examined by a startup flow experiment at various shear rates. The yield stress of MFTs is estimated by the steady shear stress values at low shear rates. Oscillatory shear (strain amplitude sweep) is also used to verify the obtained yield stress value. MFT samples exhibit thixotropy and a positive hysteresis loop at short shearing time intervals in increasing and decreasing stepwise shear rate tests. The observed hysteresis loops and thixotropy disappear by increasing the shearing time intervals, as the system reaches its equilibrium steady-state structure. The time-dependent rheological behavior of MFTs is quantified by a structural kinetics model through the dimensionless structure parameter, λ. [Toorman, “Modelling the thixotropic behaviour of dense cohesive sediment suspensions,” Rheol. Acta 36, 56–65 (1997).] The kinetic parameters are estimated based on steady-state stresses, elucidating the relative effects of shear rate and Brownian motion on buildup and breakdown of the structure. The flow behavior of MFTs predicted by the structural kinetics model is in agreement with the experimental data.

Reformulation of a phenomenological model for symmetric rate-independent hysteresis

The present paper enhances, both theoretically and numerically, a recent uniaxial phenomenological model aiming to reproduce complex hysteretic behaviors of seismic isolation devices, including steel- and fiber-reinforced elastomeric bearings, presenting smooth hysteresis loops with hardening and/or softening regions. The investigated constitutive model is based on five parameters that can be directly related to the experimentally observed hysteresis loops. Moreover, because of its analytical nature, the presented formulation is capable of computing in closed form the generalized response relevant to any displacement increment starting from a known equilibrium state. Hence, differently from the original differential formulation of the investigated model as well as from popular materials such as the celebrated Bouc–Wen, the presented formulation does not require any iterative strategy for computing the hysteretic force. Finally, the investigated model is validated by numerical simulations compared with experimental tests selected from the literature.

Enhanced electrical and ferrimagnetic properties of bismuth substituted yttrium iron garnets

Y3-xBixFe5O12 (0 ≤ x ≤ 1.0) powders are successfully prepared by sol-gel auto-combustion method. The structural, morphological, electrical and magnetic properties of bismuth substituted YIG are systematically studied and reported. The phase formation and position of vibrational modes are studied using XRD, FTIR and Raman Spectroscopy respectively. The XRD patterns of Bi-YIG powders confirm the formation of polycrystalline, single phasic and cubic garnet structure with average crystallite size around 39 nm. FTIR spectra show well resolved bands corresponding to the tetrahedral and octahedral voids of Fe–O in YIG which is characteristic of garnets. The observed translational Raman active vibrational modes confirm the presence of cubic YIG phase. SEM micrographs reveal the formation of adense homogenous network of spherical shaped Y3-xBixFe5O12 grains. Magnetic properties of Bi-YIG show an enhancement compared to the host YIG, confirming the presence of ferrimagnetic ordering at room temperature. The observation of hysteresis loop along with low coercivities are typical of soft magnetic materials. Impedance measurements of Bi-YIG show an increase in electrical resistance up to two orders compared to YIG. The Bi-YIG sample having x = 0.6 exhibits a low dielectric loss equal to 0.045 and a low conductivity of the order of 10−6 Scm−1 at 100 kHz. The observations from magnetic and electrical studies illustrate the distinct role played by bismuth ions in the YIG lattice making it a potential candidate for microwave and magnetic-optical applications.

Origin of the hysteresis of magnetoconductance in a supramolecular spin-valve based on aTbPc2single-molecule magnet

We present a time-dependent microscopic model for Coulomb blockade transport through an experimentally realized supramolecular spin-valve device driven by an oscillating magnetic field, in which the $4f$-electron magnetic states of an array of $\mathrm{Tb}{\mathrm{Pc}}_{2}$ single-molecule magnets (SMMs) were observed to modulate a sequential tunneling current through an underlying substrate nanoconstriction. Our model elucidates the dynamical mechanism at the origin of the observed hysteresis loops of the magnetoconductance, a signature of the SMM-modulated spin-valve effect, in terms of a phonon-assisted multi-spin-reversal cascade relaxation process, which mediates the switching of the device between the two conductive all-parallel spin configurations of the SMM array. Moreover, our proposed model can explain the zero-bias giant magnetoresistive transport gap measured in this device, solely within the incoherent transport regime, consistently with the experimental observations, as opposed to previous interpretations invoking Fano-resonance conductance suppression within a coherent ballistic transport regime. Finally, according to the proposed Coulomb blockade scenario, the SMM-mediated giant magnetoresistance effect is predicted to increase with the number of SMMs aligned on the nanoconstriction surface, on account of the increased number of intermediate nonconducting spin-flip states intervening in the phonon-assisted multi-spin-reversal cascade relaxation process necessary to switch between the two conducting all-parallel SMM spin configurations.

Spin structure at zero magnetic field and field-induced spin reorientation transitions in a layered organic canted antiferromagnet bordering a superconducting phase

We attempted to assign the spin structure of a layered organic antiferromagnet, $\ensuremath{\kappa}$-(d8-BEDT-${\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Br}$, which is a key material located closest to the Mott boundary at ambient pressure among this family of compounds, by investigating its macroscopic magnetization thoroughly, motivated by a recent successful assignment of the spin structure of an isostructural material, $\ensuremath{\kappa}$-(BEDT-${\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Cl}$ [BEDT-TTF and d8-BEDT-TTF are bis(ethylenedithio)tetrathiafulvalene and its deuterated molecule, respectively]. We measured the isothermal magnetization after careful choice of the measurement temperatures and cooling speed at around 80 K, so that the magnetism of the antiferromagnetic phase can be effectively extracted. Consequently, we observed hysteresis loops signifying ferromagnetism and steplike behavior when the magnetic field applied parallel to the crystallographic $b$ and $a$ axes was swept, respectively. The possible spin structure consistent with these results was discussed in terms of probable interactions between the spins, such as exchange interactions and the Dzyaloshinskii-Moriya interaction. Eventually, we asserted that $\ensuremath{\kappa}$-(d8-BEDT-${\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Br}$ has a spin structure with the easy axis being the $c$ axis and the net canted moment parallel to the $b$ axis, which is surprisingly different from that of $\ensuremath{\kappa}$-(BEDT-${\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Cl}$. We suggested that this difference originates from the difference of the sign of the interlayer interaction between the two materials. We also elucidated the overall picture of the magnetization processes of this material under the magnetic fields parallel to the three principle axes, which are also in contrast to those of $\ensuremath{\kappa}$-(BEDT-${\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Cl}$. In particular, the spin-reverse transition at which half of the spins rotate by ${180}^{\ensuremath{\circ}}$ was not induced by the $b$-axis magnetic field, as in the case of $\ensuremath{\kappa}$-(BEDT-${\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Cl}$, but by the $a$-axis magnetic field. Finally, numerical simulations and magnetic symmetry analysis enabled us to confirm the validity of the spin structures proposed for the two antiferromagnets under zero and high magnetic fields.

Estimating Preisach Density via Subset Selection

Preisach density is drawing increasing attention for interpreting material properties for memory and storage electronics. Preisach density can be linked to the observed hysteresis loops via the Preisach model that is based on the superposition of relay operators. Reconstructing Preisach density from hysteresis is an ill-posed problem with nonunique solutions. To alleviate ambiguities, we address Preisach density reconstruction as a constrained subset selection task utilizing structured sparsity regularizations. We validate our approach under various simulation settings and apply it on experimental band-excitation piezoresponse spectroscopy (BEPS) datasets to gain insights in microstructure-dependent properties of the tip-surface contact.

Crystal Growth Hysteresis in Spiral Growth

We demonstrated numerical simulations of impurity-induced crystal growth hysteresis in spiral growth. The numerical scheme combines two different methods: the phase-field method for step dynamics and the Monte Carlo method for random impurity adsorption. We manually changed the supersaturation (down and up) and repeated this cycle to monitor the time variation of the normal growth rate. We found that the growth rate suddenly drops to almost zero as the supersaturation decreases, and it swiftly recovers as the supersaturation subsequently increases. We confirmed that the critical supersaturation at which the growth rate recovered is distinguishably larger than that at which the crystal growth stopped. The critical supersaturations were found to be consistent with those predicted by the mean field theory for spiral growth if the period of the down-and-up cycle of supersaturation was chosen appropriately. We also applied the mean field theory to the observed hysteresis loops to evaluate some physical quantit...

Volumetric Measurements of Methane-Coal Adsorption and Desorption Isotherms—Effects of Equations of State and Implication for Initial Gas Reserves

This study presents the effects of equations of state (EOSs) on methane adsorption capacity, sorption hysteresis and initial gas reserves of a medium volatile bituminous coal. The sorption experiments were performed, at temperatures of 25 °C and 40 °C and up to 7MPa pressure, using a high-pressure volumetric analyzer (HPVA-II). The measured isotherms were parameterized with the modified (three-parameter) Langmuir model. Gas compressibility factors were calculated using six popular equations of state and the results were compared with those obtained using gas compressibility factors from NIST-Refprop® (which implies McCarty and Arp’s EOS for Z-factor of helium and Setzmann and Wagner’s EOS for that of methane). Significant variations were observed in the resulting isotherms and associated model parameters with EOS. Negligible hysteresis was observed with NIST-refprop at both experimental temperatures, with the desorption isotherm being slightly lower than the adsorption isotherm at 25 °C. Compared to NIST-refprop, it was observed that equations of state that gave lower values of Z-factor for methane resulted in “positive hysteresis”, (one in which the desorption isotherm is above the corresponding adsorption curve) and the more negatively deviated the Z-factors are, the bigger the observed hysteresis loop. Conversely, equations of state that gave positively deviated Z-factors of methane relatively produced “negative hysteresis” loops where the desorption isotherms are lower than the corresponding adsorption isotherms. Adsorbed gas accounted for over 90% of the calculated original gas in place (OGIP) and the larger the Langmuir volume, the larger the proportion of OGIP that was adsorbed.

Evidence of weak ferromagnetic and antiferromagnetic interaction at low temperature in Pb(Fe2/3W1/3)O3 multiferroic

Disordered magnetoelectric Pb(Fe2/3W1/3)O3 (PFW) was synthesized through columbite solid state reaction method in pure perovskite phase. Saturation magnetization of 0.013μB/f. u. was observed at 5 K, with a clear opening in the magnetic hysteresis loop around the origin. Temperature dependent magnetic susceptibility (χ) measurements revealed two different magnetic orderings, TN1 ∼ 350 K and another cusp, TN2 below 20 K. The neutron diffraction studies were carried out at different temperatures to understand the existence of the controversial TN2. The variation in the magnetic peak intensity clearly show that while decreasing temperature from 300 K to 2 K the intensity of the magnetic peak increases. This observation along with the observation of hysteresis loop at temperature below 20 K and the cusp in magnetic susceptibility data, confirms the existence of interaction between weak ferromagnetism and antiferromagnetism rather than spin-glassy nature or magnetic clusters.

Family of [Ln4Mn8] (Ln = Gd, Tb, Dy, Ho) and Y4Mn8 single-molecule magnets from the use of 2-(pyridine-2-yl)propan-2-ol

The syntheses, structures and magnetic properties are reported of a new family of [Ln4Mn8O8(O2CPh)16(dmhmp)4] (Ln = Gd (1), Tb (2), Dy (3), Ho (4)) complexes obtained from the use in Mn–Ln chemistry of 2-(pyridine-2-yl)propan-2-ol (dmhmpH), a bulkier derivative of 2-(hydroxymethyl)pyridine (hmpH) containing a CMe2OH arm instead of CH2OH. Complexes 1–4 were obtained from the reaction of Mn(O2CPh)2, Ln(NO3)3, dmhmpH and NEt3 in a 2:1:2:4 molar ratio in MeCN/MeOH (24:2 mL), and the corresponding reaction with Y(NO3)3 gave [Y4Mn8O8(O2CPh)16(dmhmp)4] (5). The crystal structures of representative complexes 1 and 5 were solved and they are isostructural, with centrosymmetric structures comprising five metal-containing layers in an ABCBA arrangement, with A = Gd(Y), B = Mn2Gd(Y), and C = Mn4. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1–5 revealed dominant antiferromagnetic interactions between the Mn8 unit and the LnIII ions. The data for 5 ostensibly indicated a well-isolated singly-degenerate ground state, but further studies suggested instead that the ground state is an S = 5 state that is near-degenerate with one or more states with S ≤ 4. Frequency-dependent ac in-phase χ′MT and out-of-phase χ″M signals indicate 3 (Dy) to possibly be an SMM, and this was confirmed by observation of hysteresis loops below 1.6 K in magnetization versus dc field scans below 2 K.

Magnetic properties and bio-medical applications in hyperthermia of lithium zinc ferrite nanoparticles integrated with reduced graphene oxide

Nanoparticles of Zn substituted lithium ferrite (Li0.31Zn0.38Fe2.31O4, LZFO) synthesized by the sol-gel route are successfully dispersed in layers of reduced graphene oxide (RGO) during the course of preparation. The analysis of X-ray diffractograms confirms the desired crystallographic phase of the nanocomposite sample of LZFO-RGO. The results of field emission scanning electron microscopy and high resolution transmission electron microscopy are consistent with the presence of dispersed nanoparticles in different layers of graphene oxide. Structural information obtained from selected area electron diffraction and nanocrystalline fringe patterns agree well with those obtained from X-ray diffractogram analysis. Mössbauer spectra recorded at 300 and 77 K suggest the presence of a fraction of superparamagnetic particles together with ferrimagnetic particles. Static magnetic measurements include observation of hysteresis loops at 300 and 5 K, magnetization vs. temperature curves under zero field cooling and field cooling conditions. Saturation magnetizations, coercive field, and saturation to remanence ratio are also evaluated. To explore the suitability of this nanocomposite for hyperthermia application, inductive heating of LZFO and LZFO-RGO is measured at different concentrations of nanoparticles. Interestingly, the inductive heating rate of LZFO nanoparticles is enhanced in the nanocomposite phase of LZFO-RGO, suggesting their high potential for hyperthermia therapy in cancer treatment.

Quantification of the Hysteresis of Macroscopic Fundamental Diagrams and Its Relationship with the Congestion Heterogeneity and Performance of a Multimodal Network

Recent studies have observed hysteresis loops in the macroscopic fundamental diagram (MFD). In particular, for the same network density, higher network flows occur during congestion onset than during congestion offset. To evaluate management strategies using the MFD, investigating the relationship between the size of these loops and network performance is needed. The existing literature has mainly discussed correlating loop width (difference in density) and height (capacity drop) with congestion heterogeneity, but has failed to prove a relationship between the capacity drop and traffic conditions. Moreover, quantification of the MFD loop in complex multimodal networks has not been investigated. The objective of this paper covers these aspects. We simulated the Sioux Falls network with different mode-share ratios (car and bus users) based on a multi-agent simulation, MATSim. We investigated the relationships between MFD loop size and congestion heterogeneity (standard deviation of density) and network performance (average passenger travel time), and found that both were directly correlated with loop width, while weakly correlated with loop height. Moreover, we divided the MFD loop into two parts according to congestion onset and offset periods and found that the heights of the two parts had opposite effects. Accordingly, we show why the relationship between capacity drop and congestion heterogeneity is not found in the literature. We also found that network performance inversely affected the height of part of the loop while the height of its other part increased with an increase in congestion heterogeneity. These results help to evaluate network performance in the presence of MFD hysteresis, leading to elaborated management decisions.

Investigating empirical implications of hysteresis in day-to-day travel time variability

Day-to-day travel time variability plays a significant role in travel time reliability. Nowadays, travelers not only seek to minimize their travel time on average, but also value its variation. The variation in the mean and the variance of travel time (across days, for the same departure time) has not been thoroughly investigated. A temporary decrease in capacity (e.g. congestion caused by an active bottleneck) leads to a quite significant difference in the variance of travel time for congestion onset and offset periods. This phenomenon results in hysteresis loops where the departure time periods in congestion offset exhibit a higher travel time variance than the ones in congestion onset with the same mean travel time. The aim of this paper is to identify empirical implications that yield to the hysteresis phenomenon in day-to-day travel times. First, empirical hysteresis loop observations are provided from two different freeway sites. Second, we investigate the potential link with the hysteresis observed in traffic networks on macroscopic fundamental diagram (MFD). Third, we build a piecewise linear function that models the evolution of travel time within the day. This allows us to decompose the problem into its components, e.g. start time of congestion, peak travel time, etc. These components, along with their probability distribution functions, are employed in a Monte Carlo simulation model to investigate their partial effects on the existence of hysteresis. Correlation among critical variables is the most influential factor in this phenomenon, which should be further investigated regarding traffic flow and traffic equilibrium principles.

La3+-induced (micro)structural changes and origin of the relaxor-like phase transition in ferroelectric lead barium niobate electroceramics

Lead barium niobate (Pb1−x Ba x Nb2O6, PBN) ferroelectric materials have been and are the subject of numerous studies in literature due to their potential for wide-ranging applications in the electronic industry. In this work, La3+-doped Pb0.56Ba0.44Nb2O6 (PBN44) electroceramics were prepared and investigated in terms of X-ray diffraction, scanning electron microscopy, thermal spectra of dielectric permittivity, Curie–Weiss law, and hysteresis loop characteristics. It was noted that La3+ doping favors the formation of orthorhombic mm2 phase in PBN44, which originally shows only the tetragonal 4mm symmetry-related phase. In particular, the PBN44 material with 1 wt% La2O3 displays (micro)structural characteristics and dielectric properties similar to those from PBN compositions lying within their morphotropic phase boundary region. Our results also show that La3+ is able to promote a change of the ferroelectric to paraelectric phase transition appearance of PBN44 from pseudo-normal to really diffuse. However, conversion to a diffuse plus relaxor transition behavior reveals directly linked to incommensurate superstructures present and dielectrically-active in PBN materials toward low temperatures, with an intrinsically frequency-dispersive dielectric response. This statement is also supported by observation of hysteresis loops showing a transformation trend to pseudo-slim-like, even in the normal-like ferroelectrics, when moving into the temperature region of incommensuration manifestation.

Numerical identification method for the non-linear viscoelastic compressible behavior of soft tissue using uniaxial tensile tests and image registration – Application to rat lung parenchyma

This paper presents an improved identification method of the constitutive properties of lung parenchyma. We aim to determine the non-linear viscoelastic behavior of lung parenchyma with a particular focus on the compressible properties - i.e. the ability to change volume. Uniaxial tensile tests are performed on living precision-cut rat lung slices. Image registration is used to compute the displacement field at the surface of the sample. The constitutive model consists of a hyperelastic potential split into volumetric and isochoric contributions and a viscous contribution. This allows for the description of the experimentally observed hysteresis loop. The identification is performed numerically: each test is simulated using the realistic geometry of the sample; the difference between the measured and computed displacements is minimized with an optimization algorithm. We compare several hyperelastic potentials and we can determine the most suitable law for rat lung parenchyma. An exponential potential or a polynomial potential with a first order term and a third or higher order term give similarly satisfactory results. The identified parameters are: for the volumetric contribution: κ=7.25e4Pa, for the exponential form: k1=4.34e3Pa, k2=5.92, for the polynomial form: C1=2.87e3Pa, C3=3.83e4Pa. The identification of the time parameter for the viscous contribution shows that it depends on the loading frequency (0.2Hz: τ=0.257s, 0.4Hz: τ=0.123s, 0.8Hz: τ=0.050s). Adding a viscous contribution significantly increases the accuracy of the identification.

Surfactant influence on interface roughness and magnetoresistance value in Fe/Cr multilayers

Effect of interfacial roughness on magnetoresistance (MR) value in Fe/Cr multilayers was studied. The Fe/Cr multilayers were prepared on a MgO(100) substrate by molecular beam deposition technique and doped with Bi and In surfactants. The morphology of the layers, especially the interface structure, was studied using conversion electron Mössbauer spectroscopy (CEMS). CEMS spectra indicate an increase in the width of interfaces of modified samples; this effect is stronger for the sample doped with In. Auger electron spectroscopy shows the segregation of the surfactant to the surface. Magnetic and magnetotransport properties of the samples were studied by the magneto-optic Kerr effect and MR measurements. The observed hysteresis loops confirm in all samples antiferromagnetic arrangement of Fe layers sandwiched between Cr while the value of MR is larger for the doped samples. It was observed that roughening of the interfaces resulted in an increase of the MR effect.

Effect of Gd-substitution on phase transition and conduction mechanism of BiFeO3

The polycrystalline sample of (Bi0.8Gd0.2)FeO3 was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray structural analysis of the sample confirms the formation of the desired compound with rhombohedral phase. The scanning electron micrograph of the sample showed uniform distribution of the plate- and rod-shaped grains. Studies of dielectric and electrical properties of the material were investigated within a wide range of temperature (25–400 °C) and frequency (1 kHz–1 MHz) using complex impedance spectroscopic method. The observation of hysteresis loop of the material confirmed that the material has a ferroelectric property at room temperature. The ac conductivity suggests that the sample obey Jonscher’s universal power law. The dc conductivity follows Arrhenius equation. Detailed studies of ac and dc conductivity show a negative temperature coefficient of resistance (NTCR) behavior of the sample.