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A polycrystalline ceramic of Pr0.7Ca0.1Sr0.2MnO3 was prosperously synthesized by the solid-state reaction method. The M(T, H) data measured at different temperatures in applied magnetic fields H = 0–30 kOe showed that the material has a ferromagnetic-paramagnetic phase transition and exhibits the crossover of the first and second order magnetic phase transitions. Above Curie temperature (TC), the χ−1(T) curve witnesses a downturn in the paramagnetic region, suggesting an appearance of the Griffiths phase. Using the modified Arrott plots and the Kouvel-Fisher methods, we have identified a set of the critical parameters (TC, β, γ, and δ) for Pr0.7Ca0.1Sr0.2MnO3 compound. The results are found to be TC = 205.5 ± 0.1 K, β = 0.191 ± 0.010, γ = 0.856 ± 0.016 and δ = 5.649 ± 0.030. It can be seen that the values of the exponents β, γ, and δ are quite close to the exponents of the tricritical mean field model. Additionally, they ​​satisfy the scaling theory well, proving their reliability. Based on obtained results, we suggest that the ferromagnetic-paramagnetic transition in Pr0.7Ca0.1Sr0.2MnO3 compound is located at a crossover of the first and second order transformations.

La0,7Ca0,3MnO3 polycrystalline were synthesized from La2O3, CaO and MnO2 powder mixture using a solid state reaction technique. The compound powders were obtained through the free sintering method at different temperatures and sintering times in order to study the influence of technological conditions on Ca doped La manganites. The most important physical features as structure, microstructure and morphology were described after X-ray diffraction investigation. Photographs of the specimen fractures were taken with SEM (scanning electron microscope) and they revealed high porosity of the tested material and great tendency for its grains to create agglomerates. Influence of doping and technological conditions on lattice parameters were studied by means of Rietvield analysis. The XRD measurements reveal that La0,7Ca0,3MnO3 has orthorhombic symmetry with Pnma space group.

Nanocrystalline La0.9A0.1Mn0.9Cr0.1O3 (A: Li, K, Na) powders have been synthesized by combustion method. The powders were used to prepare ceramics by high-pressure low-temperature sintering technique. For all samples the structure, elemental composition and morphology were studied using X-ray diffraction (XRD), Raman spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDS) and Scanning electron microscopy (SEM). Magnetic properties were studied using magnetometry methods and the valency changes of the cations after alkali ions doping were studied using X-ray photoelectron spectroscopy (XPS). The influence of the sintering pressure on the structural and magnetic properties of the manganites doped with different alkali ions and chromium was also investigated. Magnetization properties were studied as a function of sintering pressure and type of the dopant. Chemical doping with alkali ions as well as external pressure significantly changed the magnetic properties of the compounds. It was found that the magnetic properties of the manganites could be predictably modified through the use of a suitable dopant element.

Advanced scientific and industrial equipment requires magnetic field sensors with decreased dimensions while keeping high sensitivity in a wide range of magnetic fields and temperatures. However, there is a lack of commercial sensors for measurements of high magnetic fields, from ∼1 T up to megagauss. Therefore, the search for advanced materials and the engineering of nanostructures exhibiting extraordinary properties or new phenomena for high magnetic field sensing applications is of great importance. The main focus of this review is the investigation of thin films, nanostructures and two-dimensional (2D) materials exhibiting non-saturating magnetoresistance up to high magnetic fields. Results of the review showed how tuning of the nanostructure and chemical composition of thin polycrystalline ferromagnetic oxide films (manganites) can result in a remarkable colossal magnetoresistance up to megagauss. Moreover, by introducing some structural disorder in different classes of materials, such as non-stoichiometric silver chalcogenides, narrow band gap semiconductors, and 2D materials such as graphene and transition metal dichalcogenides, the possibility to increase the linear magnetoresistive response range up to very strong magnetic fields (50 T and more) and over a large range of temperatures was demonstrated. Approaches for the tailoring of the magnetoresistive properties of these materials and nanostructures for high magnetic field sensor applications were discussed and future perspectives were outlined.

The influence of the synthesis method on structural, magnetic and magnetocaloric properties of the La0.5Ca0.5Mn0.95V0.05O3 compound has been investigated. The compound was prepared by glycine nitrate process (GNP) and compared to counterparts obtained with solid-state route (S-S) and ball milling (B-M). The structural analysis shows a pure and single-orthorhombic crystalline phase for the GNP compound. A secondary phase LaVO4 was detected for S-S and B-M samples. From magnetization versus temperature analysis, different magnetic behaviors were distinguished when moving from one technique to another. The nature of transition was determined and a crossover from second order to first-order magnetic transition was observed with the decrease of crystallite size. Landau theory was performed to confirm the order of magnetic transition of the sample consistent with the Banerjee criterion. The magnetic entropy change (ΔSm) and the relative cooling power RCP, which decreased by reducing the particle size, were calculated. [ABSTRACT FROM AUTHOR]

Electron‐doped La0.9Hf0.1MnO3 thin films are epitaxially integrated onto 0.7Pb(Mg1/3Nb2/3)O3−0.3PbTiO3 single‐crystalline ferroelectric substrates to construct multiferroic heterostructures. By applying a light field and not just changing temperature, the relative magnitude of the electric‐field‐generated lattice strain effect and interfacial charge effect is identified to be controllable. Moreover, the electric field can enhance the photoresistance effect by 26%. This, accompanied by light‐tunable electroresistance effect, intimate interaction between the electric‐field‐generated and light‐generated effects is demonstrated. Herein, a route to achieve low‐power multifield (light and electric field) control of electronic transport in electron‐doped perovskite manganites is provided. [ABSTRACT FROM AUTHOR]

We have investigated the influence of the disorder on the resistive relaxation effects in the Sm1-aSraMnO3 system where a is the fraction of the alkaline element. The disorder was introduced through chemical substitution of Mn sites with Fe doping, Ru doping, or forming composite structures by adding small fractions of BaTiO3. These three routes of adding disorder lead to a distinct behavior of Tc and TMIT that depends on the concentrations and types of dopants. All the samples with a measurable zero-field resistive relaxation effect exhibited two peaks in the temperature dependence of the relaxation rates. In particular, a negative peak is found at low temperatures near the onset temperature of anti-ferromagnetic ordering while a positive peak is found near the metal–insulator transition temperature. In an attempt to quantify the strength of the disorder, we have determined the ΔT for each sample where ΔT is defined as the difference in the metal–insulator transition temperature (TMIT) obtained from the warming and cooling curves in the temperature dependence of the resistivity. The magnitudes of the peaks increase in an exponential-like manner with the increasing thermal hysteresis width ΔT, which is a measure of the extent of the inhomogeneous magnetic state or disorder in the manganite system. On the other hand, the Ru substitution of Sm1-aSraMnO3 (SGSMO) reduced the thermal hysteresis width ΔT substantially and subsequently the relaxation rates. Our observations revealed a clear relationship between the quenched disorder and the resistive metastability in manganites. [ABSTRACT FROM AUTHOR]

In insulating compounds R1-xAxMnO3, the role of orbital ordering in magnetic competition is emphasized. The conditions of ordered state's destruction are estimated. The ranges of orbital structure mixing angles to form frustrated or low-dimensional magnetic structures are determined. The influence of nonlinear and nonlocal terms of vibronic interaction on orbital ordering and magnetic structure are discussed. The possible magnetic structures are described. [ABSTRACT FROM AUTHOR]

The structural and electrical properties of Gd1−x Sr x MnO3 manganites pellets with different doping concentrations x (= 0.2,0.3,0.4,0.5) are modified using an easy low-pressure plasma irradiation method. Powder x-ray diffraction studies of the samples revealed that lattice parameters a and c increase with doping as well as plasma exposure except for x = 0.5 for which a decreases. On the contrary, lattice parameter b decreases with doping as well as plasma exposure and is more pronounced. The crystallite size increases with increasing doping concentration both with or without plasma exposure. Plasma exposure tends to decrease the Mn–O–Mn bond angle as well as the Mn–O bond length. The temperature-dependent electrical resistivity of samples reveals that the pristine Gd1−x Sr x MnO3 exhibits insulating behavior for all the doping concentrations. However, the resistivity is enhanced at low temperature for all samples after plasma exposure. The variation of electrical resistivity after plasma exposure may be attributed to the disorder near the grain boundaries and cell volume. The resistivity behavior is unaffected by plasma exposure for all samples. The small polaron hoping model explains the conduction mechanism at high temperature while the conduction at low temperature is attributed to variable range polarons. [ABSTRACT FROM AUTHOR]

The effect of green (514 nm) and infrared (1028 nm) pulsed laser light on the electrical resistance at the interface of a Ba0.8Sr0.2TiO3/LaMnO3 heterostructure is studied. Illumination is shown to cause, at low temperatures of 80–200 K, an increase in the resistance along the interface by a value of up to 2–15% from the initial value. The characteristic time of the transient dynamics of varying the resistance is 4–12 s. The effect of the photoinduced resistance is observed either at both green and infrared illumination; in this case, the effect of green-light illumination is significantly higher. Illumination is carried out by a defocused laser beam; thus, the effect cannot be related to heating of the interface region. The effects are shown to add up during simultaneous illumination with green and infrared light. [ABSTRACT FROM AUTHOR]

The interesting transport and magnetic properties in manganites depend sensitively on the nucleation and growth of electronic phase-separated domains. By fabricating antidot arrays in La0.325Pr0.3Ca0.375MnO3 (LPCMO) epitaxial thin films, we create ordered arrays of micrometer-sized ferromagnetic metallic (FMM) rings in the LPCMO films that lead to dramatically increased metal-insulator transition temperatures and reduced resistances. The FMM rings emerge from the edges of the antidots where the lattice symmetry is broken. Based on our Monte Carlo simulation, these FMM rings assist the nucleation and growth of FMM phase domains increasing the metal-insulator transition with decreasing temperature or increasing magnetic field. This study points to a way in which electronic phase separation in manganites can be artificially controlled without changing chemical composition or applying external field.

The kinetics of magnetization reversal in LSMO/YBCO hybrid nanostructures in longitudinal and perpendicular magnetic fields is investigated at temperatures above and below that of the superconducting transition. It is shown that, in a perpendicular magnetic field, the presence of the ferromagnetic layer in the structure leads only to an increase in the local pinning of vortices and inhomogeneity of the penetrating magnetic flux due to its dendritic penetration into YBCO. However, in a longitudinal field, various patterns of magnetic-flux penetration into YBCO are observed, which are determined by the magnetic prehistory, i.e., by the type of magnetic-domain structure formed in LSMO after magnetization reversal above the critical temperature of the superconductor. In particular, the longitudinal magnetic field applied to the structure is transformed either to macroscopic droplets with an alternating perpendicular magnetic flux or to extended longitudinal waves of the perpendicular flux, which decay upon propagation deep into the superconductor; i.e., in both cases, vortices and antivortices perpendicular to the superconductor film plane enter the superconductor. The results obtained are qualitatively explained by distortion of the configuration of the longitudinal magnetic field applied to the heterostructure by a ferromagnetic layer deposited under the superconducting layer. [ABSTRACT FROM AUTHOR]

In this work, the manganite's magnetocaloric properties are studied by changing their chemical composition for a group La 0.8- x Sm x Sr 0.2 MnO 3 (x = 0.0, 0.05, 0.10, and 0.15) ceramic synthesized by the solid-state reaction method. According to the X-ray powder diffraction (XRD) analysis, no sign of a secondary phase is detected. It is found that the prepared samples are formed in the rhombohedral crystal structure with an R -3 c space group. There is a decreasing trend in the unit cell volume, which indicates the gradual replacement of Sm in La sites. The results obtained from the energy-dispersive X-ray (EDAX) spectroscopy test indicated that the ratio of elements in the compounds is close to their nominal values. Based on the M measurements (upon the change of temperature) of the as-prepared specimens, an FM transition is observed. The transition temperature decreases upon the increase of the x value. The measured magnetic entropies of all the La 0.8- x Sm x Sr 0.2 MnO 3 samples are an illustration of a magnetocaloric impact on these compounds. This observation introduces La 0.8- x Sm x Sr 0.2 MnO 3 as a potential candidate for applications related to magnetic refrigeration. [ABSTRACT FROM AUTHOR]

[Display omitted] • The rhombohedral La 0.8 K 0.2-x Li x MnO 3 (0 ≤ x ≤ 0.075) samples were synthesized using the sol–gel technique at low temperature. • All the samples exhibit a second order paramagnetic-ferromagnetic transition with decreasing temperature. • Δ S M Max under an applied magnetic field change of 5 T is found to be 3.19, 3.51, 2.39 and 2.24 J kg−1 K−1 for x = 0, 0.025, 0.05 and 0.075 respectively • The RCP (S) of La 0.8 K 0.175 Li 0.025 MnO 3 sample is 320.5 J/kg under a magnetic field change of 5 T. In this study we report the effect of lithium substitution on the structural, magnetic and magnetocaloric properties of La 0.8 K 0.2-x Li x MnO 3 (0 ≤ x ≤ 0.075) samples synthesized by the sol–gel technique at low temperature. The investigated compounds crystallize in a rhombohedral system with R 3 ¯ c space group. The thermal variation of the magnetization under an applied magnetic field of 0.05 T showed that all our compounds exhibited a paramagnetic to ferromagnetic transition with decreasing temperature. With increasing lithium content, the Curie temperature T C , decreases from 287.4 K for x = 0 to 172.6 K for x = 0.075. The maximum of the magnetic entropy change, - Δ S M Max , is found to be 3.19, 3.51, 2.39 and 2.24 J kg−1 K−1 in a magnetic field change of 5 T for x = 0, 0.025, 0.05 and 0.075 respectively. The La 0.8 K 0.175 Li 0.025 MnO 3 sample displays a higher maximum relative cooling power value of 320.5 J kg−1, equal to 78 % of that of gadolinium. Technically, this large value associated to a T C of 270 K makes the present sample very promising for magnetic refrigeration technology below room temperature. [ABSTRACT FROM AUTHOR]

We report the structural, magnetic, and magnetocaloric properties of Bismuth (Bi)-substituted manganite La0.85-xBixNa0.15MnO3 (x=0, 0.1, 0.2, 0.25, and 0.3). X-ray diffraction data implicates the rhombohedral structure with R 3 ¯ c space group. Bi2O3 has helped in ensuring phase pure, densified compounds even at low sintering temperature and hence avoiding the evaporation of volatile sodium. The increase in grain size and decrease in magnetic transition temperature (TC) are due to the Bi chemical activity and electronic structure. The samples have shown indirect magnetic transformation from soft ferromagnet to canted ferromagnet/antiferromagnet with Bi. Griffiths phase-like behavior in the inverse magnetic susceptibility was observed for x=0.1; with further increase in Bi, the samples are found to develop the antiferromagnetic competing phase. The phenomenological model was used to model the thermomagnetic behavior of all the samples. The sample with x=0.1 shows an increase in magnetic entropy change upon Bi substitution and the maximum of magnetic entropy change is seen at 275K emphasizing its potential in room temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In this work, manganite ceramics of Sm0.7-xCexSr0.3MnO3 (0 ≤ x ≤ 0.3) are prepared by a citrate sol–gel chemical route and characterized. The structure of the obtained samples is refined in the orthorhombic system with the Pnma space group. The doping causes a change in the lattice parameters leading to a decrease in the cell volume. It also increases slightly the grain size of the crystallites. The temperature dependence of resistivity reveals a metal–insulator transition for all samples. The doping shifts the temperature of this transition towards high values. The extracted magnetoresistance for a 5 T magnetic field is enhanced by doping. The highest obtained value increases from 66.70% for x = 0 to 97.96% for x = 0.3. [ABSTRACT FROM AUTHOR]

Our central focus in this research work is upon the study of the effect of lightly Ti4+ doping ions on the critical behavior of La0.55Pr0.1Sr0.35Mn1 − xTixO3 (x = 0.0 and 0.05) perovskite compounds synthesized by the modified sol-gel Pechini method. The two samples underwent a second-order paramagnetic to ferromagnetic transition as temperature decreased. The critical exponents (beta, gamma, and delta) were determined using various methods based all on the measure of magnetization around the Curie temperature TC. With the Modified Arrot plot method, the critical exponents were found to be β = 0.254, γ = 0.934 at TC = 308.9 K and β = 0.347, γ = 1.29 at TC = 287.8 K for xTi = 0.0 and xTi = 0.05 samples, respectively. Thus, the magnetic interactions satisfied with the prediction of 3-D Tricritical mean field model for xTi = 0.0 and the Heisenberg model forxTi = 0.05. Therefore, the universality class was affected by Ti doping. This result was confirmed by the Kouvel-Fisher method which gave values of β = 0.269, γ = 1.024 at TC = 309.0 K and β = 0.356, γ = 1.31 at TC = 288.3 K for xTi = 0.0 and xTi = 0.05 samples, respectively. These values were checked by the Widom's scaling equation δ = 1 + γ/β and the Stanley's scaling equation M H ε = ε β f ± H ε β + γ . The coupling between critical exponents and magnetocaloric effect was studied by analysis of the field dependence of magnetic entropy change which showed the law dependence, namely, ∆SM ∝ Hn. [ABSTRACT FROM AUTHOR]

The effects of K+ substitution at the Ba-site on the structural, magnetic, and electrical properties and magnetoresistance (MR) of La0.7Ba0.3−xKxMnO3 (x = 0 and 0.04) manganites prepared via the solid-state method were investigated. Rietveld refinement of X-ray diffraction data confirmed that both samples were crystallized in the rhombohedral structure with the R3c¯ space group. In addition, the unit cell volume, V, and the average grain size also increased with K+ ions. Magnetization versus applied field (M–H) measurement was carried out, and the saturation magnetization (Ms) was found to increase from 1.81 μB/f.u. (x = 0) to 4.11 μB /f.u. (x = 0.04), implying that K+ ions strengthened the ferromagnetic (FM) interaction. Furthermore, the metal–insulator transition temperature, TMI, increased from 257 K (x = 0) to 271 K (x = 0.04). The observed behaviour may be related to the enhancement of double-exchange (DE) interaction due to the increase in Mn-O-Mn bond angle and electronic bandwidth (W), favouring the increasing rate of the eg electron hopping process. The fitting of the electrical resistivity data in the metallic region describes the significance of residual resistivity, electron–electron and electron–magnon scattering processes to elucidate the electronic transport properties. Within the insulating region, variable range hopping (VRH) and small polaron hopping (SPH) models are proposed to describe the conduction mechanism.

The effect of Dy doping on CaMnO3 (CDMO) has been thoroughly investigated. The room-temperature structure, low-temperature magnetic transitions, and high-temperature electrical properties of CDMO were studied using X-ray diffraction, magnetization, and dielectric techniques. The CDMO exhibits an orthorhombic structure with Pnma symmetry. The low-temperature magnetic susceptibility data show the ferromagnetic domains embedded in the antiferromagnetic structure (G-type), and it confirms the Neel temperature (TN) approximately 55 K. Temperature-dependent dielectric data measured using a few selected frequencies show a high dielectric constant ~ 29,108,808 at 1 kHz. The presence of a high dielectric constant at the lower frequency side can be attributed to the space charge polarization (SCP) and compositional disorder (heterogeneity) in the compounds. The impedance cole-cole plot shows a depressed semicircle; mathematically these data were fitted by the Kohlrausch-Williams-Watt model. From this model obtained two mechanisms: (i) the electric modulus divulges the CDMO ceramic tails the Non-Debye type of relaxation and (ii) the electric modulus peak shifting evidence the charge carrier mobility from long range to short range. High-temperature dielectric, resistivity, and conductivity data show a clear anomaly around 461 K, owing to metal to insulator transition. [ABSTRACT FROM AUTHOR]

In the present study, we present our investigation on the structure and magnetocaloric effect (MCE) of La0.7Sr0.3Mn1−xCuxO3 (x = 0.08 and 0.12) compounds prepared by a conventional solid-state method. X-ray diffraction patterns indicate that the samples have a rhombohedral structure with the R 3 ¯ c space group. The Curie temperature decreases with increasing Cu concentration. Using a phenomenological model, the MCE of the two samples was predicted from the experimental magnetization data measured at magnetic fields of 3 kOe, 5 kOe, 8 kOe, and 10 kOe. The type of second-order magnetic phase transition of the samples is confirmed by the collapse of the entire master curve of magnetic entropy change in the same plot. Our investigation on the magnetocaloric behavior of the title compounds suggests that they are suitable candidates for application to near-room temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

This paper presents structural, magnetic, and electrical characteristics of manganites in the system (0 ≤ x ≤ 0.1) synthesized by solid-state reactions. Sintering was performed in air at 1423 K. Samples with stoichiometric oxygen content (γ = 0) were obtained by annealing at 1223 K and partial oxygen pressure of 0.1 Pa. All studied manganites have rhombohedral structure. With an increase in magnesium content, the unit cell volume decreases, and annealed samples have a larger cell volume than the initial (sintered) manganites containing over-stoichiometric oxygen. The ratio of lattice parameters c/a is practically unchanged. Curie point of manganites decreases in general with an increase in magnesium content, showing weakly expressed plateau in the region of 0.025 < x < 0.075. Magnetization and "metal–semiconductor" transition temperature have maximum values at x = 0, then change non-monotonically, and at x > 0.075 fall sharply. Manganite, which contains the largest amount of magnesium, has the highest resistance at temperatures below 180 K and is characterized by the largest width of the temperature interval of "ferromagnetic–paramagnetic" transition, which indicates the existence of magnetic inhomogeneities. Electromagnetic parameters of initial and annealed samples differ slightly. A number of effects and competing factors that determine complicated dependencies of electromagnetic characteristics of manganites in this system on the composition are considered: inhomogeneous distribution of Mg2+ and Fe3+ ions; increased concentration of Mn4+ ions and their shielding by magnesium ions; violation of double exchange interaction between Mn4+ and Mn3+ by ions replacing manganese; difference in magnetic moments of the latter; changes in characteristics of magnetic inhomogeneities. [ABSTRACT FROM AUTHOR]

Magnetic circular dichroism (MCD) spectroscopy for manganite films of various compositions and morphologies has been studied in the range of 1.2-3.7 eV. The primary focus was on the temperature behavior of the MCD spectra, as well as the magnetization and resistivity of the films. The data obtained were analyzed in comparison with magneto-optical spectroscopy of the Kerr rotation (KR) on both single crystal and thin film of manganites. It has been established that the MCD response at 2.3 eV is typical for manganites transitioning into a conducting state. Consequently, it reflects a change in the band structure of the material. This response is also observed in the KR spectrum of manganites in the range 2.3-2.6 eV below the metal-insulator transition temperature. These findings complement the understanding of the electronic structure of manganites in general. Moreover, they also provide a basis for the search for new functional materials., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) phase, where conducting electrons localize and create a long range order giving rise to insulator-like behavior. One of the major open questions in manganites is the exact origin of this insulating behavior. Here we report a dc resistivity and magnetization study on manganite La1−xCaxMnO3 ceramic samples with different grain size, at the very boundary between CO/AFM insulating and FM metallic phases x=0.5. Clear signatures of variable range hopping (VRH) are discerned in resistivity, implying the disorder-induced (Anderson) localization of conducting electrons. A significant increase of disorder associated with the reduction in grain size, however, pushes the system in the opposite direction from the Anderson localization scenario, resulting in a drastic decrease of resistivity, collapse of the VRH, suppression of the CO/AFM phase and growth of an FM contribution. These contradictory results are interpreted within the standard core-shell model and recent theories of Anderson localization of interacting particles.

In this communication, structural and electrical properties have been discussed for chemically grown ZnO–LaMnO3 (ZnO–LMO) nanocomposites. Nanocomposites were prepared by mixing the different weights, i.e., ratios of ZnO to LMO, 100:0, 95:5, 90:10, 85:15, and 0:100 wt% of ZnO:LMO in their composite form. X-ray diffraction (XRD) measurement shows that all the pure and composite samples possess single-phase nature without any detectable impurity. Particle size and shape were identified using transmission electron microscopy (TEM) measurement. Frequency-dependent dielectric constant (ε′), loss tangent (tanδ), real and imaginary parts of the electric modulus (M′ and M′′), and a.c. conductivity have been carried out at room temperature for all the samples. Dielectric behavior has been understood in the context of universal dielectric relaxation (UDR) model and relaxation mechanism fits well throughout the frequency range studied. Variation in a.c. conductivity has been discussed on the basis of Jonscher's universal power law. [ABSTRACT FROM AUTHOR]

The pristine and barium (Ba2+) doped YMnO3 (Y1−xBaxMnO3; x = 0.00 and 0.05) ceramic samples were synthesized through the solid-state reaction method. The X-ray diffraction, Raman spectroscopy, and scanning electron microscopy were performed for the structural and morphological studies. The electrical transport properties were investigated using dielectric and modulus spectroscopy. The XRD patterns of the titled ceramics have shown the monophasic hexagonal structure having P63cm space group symmetry. The average crystallite size is found to decrease on partial substitution of Ba2+ cation. Raman spectroscopy was performed to observe the local disorder and variation in the modes with the introduction of dopant in the pristine ceramic. The surface morphology displays the formation of non-uniform grains in the ceramics. The dielectric spectroscopy reveals a decreasing trend in both the dielectric constant and dissipation factor with increasing frequency. It indicates the significant role played by the space charge polarization. The electrical modulus study of the ceramics was also performed to explore the electrical transport phenomenon. The present study reports the enhanced dielectric nature of doped materials. [ABSTRACT FROM AUTHOR]

In the present work, GdMnO3 samples were synthesized by acetate precursor based modified sol–gel method with different sintering temperatures. XRD was performed to understand the structural properties of the samples which imply that samples possess single phasic nature with orthorhombic structure. UV–vis absorption spectrum was analyzed using Tauc's relation which gives a direct band gap of ∼ 0.98 eV for the GdMnO3 sample sintered at 1100 °C. Variation in dielectric and impedance with sintering temperature has been discussed in the context of oxygen vacancies and ZDE mechanism. [ABSTRACT FROM AUTHOR]

In the present work, GdMnO3 samples were synthesized by acetate precursor based modified sol–gel method with different sintering temperatures. XRD was performed to understand the structural properties of the samples which imply that samples possess single phasic nature with orthorhombic structure. UV–vis absorption spectrum was analyzed using Tauc's relation which gives a direct band gap of ∼ 0.98 eV for the GdMnO3 sample sintered at 1100 °C. Variation in dielectric and impedance with sintering temperature has been discussed in the context of oxygen vacancies and ZDE mechanism. [ABSTRACT FROM AUTHOR]

The polycrystalline samples (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 were prepared by the solid-state reaction method. Magnetization measurements versus temperature were performed in order to investigate the magnetic properties such as the metamagnetic transition. The transition temperature estimated from the maximum of dM/dH is found sensitive to disorder σ2 leading to the formation of an inhomogeneous metastable state and to subsequent magnetization jumps. The peak temperature coefficient of the resistivity improved significantly from 1.54 to 8.21% K−1 due to the increase in disorder. These findings suggest that (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 ceramics can be used to prepare uncooled infrared bolometers. [ABSTRACT FROM AUTHOR]

The aim of the work was to check how the introduction of alkali and cobalt ions into a manganese structure can affect the structural disorder and, in consequence, lead to the changes (improvements) of magnetic properties. The high-pressure sintering technique was applied to check if the external factor can modify the magnetization of manganites. Nanocrystalline La0.9A0.1Mn0.9Co0.1O3 (where A is Li, K, Na) powders were synthesized by the combustion technique. The respective powders were used for nanoceramics preparation by the high-pressure sintering technique. The structure and morphology of the compounds were studied by X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Magnetization studies for all compounds were performed in order to check the changes induced by either codoping or the sintering pressure. It was found that the type of the dopant ion and sintering pressure produced significant changes to the magnetic properties of the studied compounds. Alkali ions lead to the stabilization of Co ions in the +2 oxidation state and the formation of positive exchange interactions Mn3+–Mn4+ and Co2+–Mn4+ and the subsequent increase in remanent magnetization. High sintering pressure leads to a decrease in grain size and reduction of long-range ferromagnetic order and lower magnetization. [ABSTRACT FROM AUTHOR]

Structural analysis, magnetocaloric properties, and theoretical investigations of the magnetocaloric effect were carried out in the crystalline La0.7Ba0.15Ag0.15MnO3 manganite prepared using sol-gel route. The phase purity and structure of this sample were checked by X-ray diffraction technique and Rietveld analysis. From magnetic measurements, the ferromagnetic to paramagnetic (FM-PM) phase transition was observed around TC = 255 K. The maximum change in magnetic entropy (∆ S M max ) and relative cooling power (RCP) extracted from magnetic measurements were 3.48 J × kg-1 × K-1 and 225 J × kg-1 at an applied magnetic field of 5 T. These magnetocaloric parameters offer to the sample the possible use in the magnetic refrigeration technology. The magnetic entropy simulation by using different theories such as the Weiss molecular mean-field theory and the Landau theory shows good correlation between the theoretical values of −∆SM(T) and the experimental ones estimated from Maxwell relation. [ABSTRACT FROM AUTHOR]

In this work, we report the effect of sintering temperature (TS) on the magnetic interactions and the critical behavior of Pr0.67Sr0.33MnO3 manganite prepared via sol–gel method (700 °C ≤ TS ≤ 1200 °C). The critical exponents study revealed that the 3D-Ising model is the best model to describe the magnetic interactions in the P1000 (TS = 1000 °C) and P1200 (TS = 1000 °C) samples. Consequently, a strong magnetic anisotropy characterizes these samples near the paramagnetic-ferromagnetic transition temperature, such anisotropy can be linked to the magnetic moment of Pr3+ ions (µ = 3.58 µB). For TS ≤ 850 °C, it becomes nearly impossible to speak about universality class due to the presence of great magnetic disorder induced by several factors like spin disordered shell in nanoparticles, magnetic frustration and Griffiths phase. Highlights: Pr0.67Sr0.33MnO3 manganite was prepared by sol–gel route with different sintering temperature (Ts) values. 3D-Ising model can describe the magnetic behavior for Ts > 850 °C. The critical analysis for nanosized specimens is not possible due to the spin disorder. [ABSTRACT FROM AUTHOR]

The effect of half substitution of diamagnetic Bi3+ with the rare earth magnetic Nd3+ ion on the magnetic and structural properties of the polycrystalline Bi0.25Nd0.25Sr0.5MnO3 and Bi0.25Nd0.25Ca0.50MnO3 was studied by X-ray and neutron diffraction complemented by magnetic measurement. We correlate the structural response of Bi0.25Nd0.25X0. 5MnO3 (X = Sr, Ca) for charging and spin ordering with a reduced amount of Bi3+, which in addition to its special contribution to itinerant eg electrons leads to a change in the average size of the A-site cations, 〈rA〉, and the mismatch between the A-site cations (size variance, σ 2). For both compounds, the corresponding charge ordering scheme and ground magnetic state of CE-type antiferromagnetic arrangement at 10 K were specified. An analysis of the data confirms that in Bi–Sr manganite a lone pair of 6s2 Bi3+ orbitals is dominant. [ABSTRACT FROM AUTHOR]

A comparative study of the field-dependent resistivity (ρ) and thermoelectric-power (TEP) of Li-doped La1-xLixMnO3+δ and Bi-doped La0.67-yBiyCa0.3MnO3 is made. The perovskite structure of the La1-xLixMnO3+δ is rhombohedrally distorted in contrast to the La0.67-yBiyCa0.3MnO3 showing orthorhombic symmetry. The metallic part of resistivity of La1-xLixMnO3+δ is best fitted with an expression ρ(T) = ρ0 + ρ4.5T 4.5 + C/sinh2(hνs/2kBT) containing small-polaron contribution (last term), involving a relaxation time due to soft optical-phonon mode. This is in sharp contrast to the resistivity of La0.67-yBiyCa0.3MnO3 where, the ρ(T) data are best fitted with the electron-magnon scattering model ρ = ρO + ρT T2.5. These results suggest the optimum requirements for the formation of optical-polaron in manganites in the metallic phase, which depends on the characteristics of the constituent A-site ion (valence-state, ionic-radii, etc.) of manganites. Unlike Li-doping, the Bi-doping does not induce any hopping site indicated from the critical analysis of the TEP data. [ABSTRACT FROM AUTHOR]

We have reported the solgel synthesis, the structural analysis, and the correlation between magnetic and electrical properties of La0.7Ba0.15Ag0.15MnO3 manganite. The phase purity and structure of this sample were checked by X-ray diffraction technique and Rietveld analysis. M(T) measurement shows a ferromagnetic (FM)-to-paramagnetic (PM) phase transition of second-order type at Curie temperature TC = 255 K. The obtained magnetocaloric parameters offer to the sample the possible use in the magnetic refrigeration technology. The resistivity data, ρ(μ0H, T), show the presence of metal–semiconductor transition and a maximum magnetoresistance (MR) value of the order of 32% at magnetic field of 5 T. The phenomenological percolation model was used to study the conduction mechanism of the sample. It has been also shown that, from analyzing the temperature and magnetic field dependences of the electrical resistivity, it is possible to predict the behavior of the magnetization as well as the change of magnetic entropy near the phase transition temperature. The obtained agreement with experimental data for this analysis is quite reasonable. [ABSTRACT FROM AUTHOR]

In this work, an overview of the Weiss molecular mean-field theory, the Bean–Rodbell model and the Landau theory is presented, providing the theoretical background for simulating the magnetocaloric properties for La0.6Ca0.2Na0.2MnO3 manganite. Results showed that sample exhibits second-order ferromagnetic (FM)–paramagnetic (PM) magnetic phase transition and relatively higher values of magnetic entropy change (−∆SM). In application point of view, this material can be used in magnetic refrigeration technology. The theoretical values of −∆SM determined using each theory agree well with the experimental ones estimated from Maxwell relations. In other part, a good agreement in the spontaneous magnetization values, Mspont(T), estimated from (−∆SM vs. M2) and (H/M vs. M2) data was found. Also, the values of the critical exponent (β) found from both methods are close and check that the mean-field model is adequate to study the MCE in La0.6Ca0.2Na0.2MnO3 sample. [ABSTRACT FROM AUTHOR]

Noncollinear spin textures such as skyrmions lead to a novel Hall effect contribution called the topological Hall effect. In recent years, research has focused on the Weyl metal SrRuO3 with topological signatures reported for SrRuO3 layers adjacent to layers with strong spin–orbit coupling. However, SrRuO3 films are known to be prone to structural modifications when interfaced with different materials. In this work the Hall effect of SrRuO3/La0.7Sr0.3MnO3 superlattices (SLs) is correlated with structural and magnetic information to study whether a topological Hall effect is induced by interfacing to ferromagnetic layers. High‐quality SLs with ultrathin layers are fabricated by pulsed laser deposition on SrTiO3 substrates. The symmetry of the SrRuO3 layers is studied by angular magnetoresistance measurements and the magnetocrystalline anisotropy by magnetization measurements. Two SLs are compared in detail, both with 8 unit cell thick SrRuO3 layers, but with La0.7Sr0.3MnO3 layers 2 and 4 unit cell thick. Only the sample with 2 unit cell thick manganite layers shows features resembling a topological Hall effect. Depending on the La0.7Sr0.3MnO3 layer thickness the SrRuO3 crystalline symmetry is orthorhombic or tetragonal. The results indicate that the topological Hall effect features arise from an intricate interplay between magnetocrystalline anisotropy and antiferromagnetic interlayer coupling. [ABSTRACT FROM AUTHOR]

In this article, we report the results of the Rietveld and impedance analysis of Eu doped La1–xEuxMnO3 (LEMO; x = 0.10, 0.30, and 0.50) perovskite manganites synthesized by solid-state reaction method. Structural studies through Rietveld analysis confirm that a mixed-phase nature of all LEM samples having a hexagonal unit cell structure with a less detectable impurity (Eu2O3) ceramics. The patterns are zanalyzed in detail with structural distortion and strain in LEM manganites ceramics. Dielectric constant and modulus are found to increase with increasing Eu concentration. The samples LEM-0.10 shows the negative capacitance at low frequency and temperature, respectively. [ABSTRACT FROM AUTHOR]

La0,7Ca0,3MnO3 polycrystalline were synthesized from La2O3, CaO and MnO2 powder mixture using a solid state reaction technique. The compound powders were obtained through the free sintering method at different temperatures and sintering times in order to study the influence of technological conditions on Ca doped La manganites. The most important physical features as structure, microstructure and morphology were described after X-ray diffraction investigation. Photographs of the specimen fractures were taken with SEM (scanning electron microscope) and they revealed high porosity of the tested material and great tendency for its grains to create agglomerates. Influence of doping and technological conditions on lattice parameters were studied by means of Rietvield analysis. The XRD measurements reveal that La0,7Ca0,3MnO3 has orthorhombic symmetry with Pnma space group. [ABSTRACT FROM AUTHOR]