Structure Of Manganites Research Articles

The visible magneto-optical response of RE1-xAxMnO3manganites: relationship with the charge component of the material.

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.

Charge carrier motion and Mn-spin coupling defining the transport behaviors and the magnetic order at DySrCaMnO3 polycrystalline ceramic

The Ca-doped Dy0.5Sr0.5MnO3 manganite was synthesized using the Sol-Gel technique. The material demonstrates semiconducting behavior across a wide range of temperatures. This behavior could be attributed to the involvement of small polaron hopping, Shklovskii-Efros variable range hopping, and Mott-variable range hopping mechanisms. The Shimakawa Model is used in the intermediate temperature range to verify the existence of multiphonons in the compound. The conductance spectra adhere to the Jonscher power law and can be elucidated by the utilization of the Jump relaxation model. The manganite structure deviated from Summerfield scaling, indicating that numerous crystalline-ordered materials possess unexplored conduction and relaxation mechanisms, unlike amorphous systems. Magnetic anomalies at around 6K were observed, indicating antiferromagnetic (AFM) interactions between Dy–Dy pairs. Another anomaly occurs at approximately 40K, indicating AFM coupling between Mn-spins.

Elektricheskaya polyarizatsiya v dvoynom manganite BiMn7O12: messbauerovskoe issledovanie na zondovykh yadrakh 57Fe

The electrical hyperfine interactions of the probe 57Fe nuclides localized in the structure of the quadruple manganite BiMn7O12 are studied by Mössbauer spectroscopy. The measurements are carried out in the temperature range 101 K T 447 K, where this manganite has a nonzero spontaneous electric polarization (Ps); moreover, this range includes the temperature (T* ≈ 240 K) of the P1 ↔ Im structural phase transition. The parameters of the hyperfine interactions of the partial spectra of the 57Fe nuclei are comprehensively analyzed, and their crystal-chemical correspondence to certain positions of Jahn–Teller Mn3+ ions in the structure of manganite is performed. The “dynamic” Born charge model is used to develop an algo rithm to construct the temperature dependence of the polarization of the crystal Ps(T) using structural data of the compound and the experimental values of the quadrupole splittings Δ(T) of the Mössbauer spectra of the 57Fe probe atoms. The Ps(T) dependences obtained on both sides of point T* are analyzed in terms of the mean-field model.

Reticulated porous lanthanum strontium manganite structures for solar thermochemical hydrogen production

Porous ceramic foams are utilized in various fields and applications due to their advantageous properties such as high porosity, high specific surface area, and controlled permeability. Non-stoichiometric oxide foams are of particular interest for the solar thermochemical production of hydrogen in directly irradiated solar receivers due to their enhanced heat transfer capabilities and structural integrity. We report the fabrication of lanthanum strontium manganite replica foams and their solar thermochemical water splitting performance. Highly porous (>80%) foams were produced with controlled structure and tested in a high temperature water splitting furnace to demonstrate stability and overall performance. The temperature profile of the burnout and sintering of the foam structure were altered based on simultaneous differential scanning calorimetry and thermal gravimetry analysis. Two-step sintering was used both to retain micron-sized pores (D50 = 0.4 μm) on the foam's struts and to limit grain growth to a grain size of ∼1 μm. The structural characteristics were confirmed by porosimetry and scanning electron microscopy. The foams were repeatedly cycled, producing approximately 200 μmol/g of H2 per cycle. Water splitting performance was tested for 50 cycles and approximately 35 h at 1400 °C. No statistical difference in the effective hydrogen production per cycle was observed, which is promising for long-term redox cycle stability.

Investigations on interface charge conduction mechanisms for chemically grown manganite – Manganite structure: Hysteretic current – Voltage characteristics

In the present study, high quality LaMnO3–δ/La0·7Ca0·3MnO3/LaAlO3 (LMO/LCMO/LAO) manganite – manganite structure was successfully prepared using low cost chemical solution deposition (CSD) method. Temperature dependent resistive switching (RS) was performed across the manganite – manganite structure and various electronic processes have been employed to understand observed RS behavior. Various theoretical models have been used to understand the charge conduction involved in the hysteretic current – voltage (I–V) characteristics at different temperatures. Charge carrier conduction processes have been investigated for separate I–V cycles of RS characteristics where thermionic emission and space charge limited conduction mechanisms have been identified as appropriate charge carrier conduction mechanisms. Temperature dependent barrier height and other obtained fitting parameters have been discussed in detail.

Waste of batteries management: Synthesis of magnetocaloric manganite compound from the REEs mixture generated during hydrometallurgical processing of NiMH batteries

In the present study, rare earth elements (REEs, i.e., La, Ce, Nd, and Pr) were hydrometallurgically recovered in oxalate form with presence of very low concentration of Co, Al, Zn and Ni from solution after processing of spent Nickel metal hydride (Ni-MH) batteries. The recovered mixture was used as alternative source in the synthesis of magnetocaloric materials. In this study, a manganite sample with general formula ABO3 was selected to be prepared since it is relatively easy to synthesize and is tuneable by adjustment of the doping concentration. The conventional solid-state reaction method was used to prepare an orthorhombic structure of manganite with presence of REE2O3 and MnO2 as secondary phases reported from x-ray pattern at room temperature. The thermomagnetic measurements showed a PM to FM transition at 184 K in a 0.01 T magnetic field that shifts to 194 K by increasing the magnetic field to 1.8 T. The magnetocaloric properties were determined by calculating the isothermal entropy change and directly measuring the adiabatic temperature change. A reversible magnetocaloric effect was observed.

Polaronic effect in the x-ray absorption spectra of La1−xCaxMnO3 manganites

X-ray absorption spectroscopy (XAS) is performed to study changes in the electronic structures of colossal magnetoresistance (CMR) and charged ordered (CO) La1−xCaxMnO3 manganites with respect to temperature. The pre-edge features in O and Mn K-edge XAS spectra, which are highly sensitive to the local distortion of MnO6 octahedral, exhibit contrasting temperature dependence between CMR and CO samples. The seemingly counter-intuitive XAS temperature dependence can be reconciled in the context of polarons. These results help identify the most relevant orbital states associated with polarons and highlight the crucial role played by polarons in understanding the electronic structures of manganites.

Room temperature magnetocaloric effect in Pr1.75Sr1.25Mn2O7 double-layered perovskite manganite system

In this work, we have studied on double-layered perovskite (Ruddlesden–Popper) manganite structure in Pr1.75Sr1.25Mn2O7 synthesised by sol–gel method. The crystal structure of the double-layered perovskite is found as tetragonal from the X-ray diffraction analysis with I4/mmm space group. A high Curie temperature, TC = 305 K is observed from the temperature dependence of magnetisation measurement. The isothermal magnetisation curves showed that magnetic phase transition is second order due to the positive slope of the Arrott plots. Maximum magnetic entropy change (ΔSM) and adiabatic temperature change (ΔTad) values are calculated as 3.99 J kg−1 K−1 and 2.1 K under external magnetic field of 70 kOe, respectively. Since our double-layered perovskite manganite sample has desired TC value and relatively high ΔSM, it can be a potential candidate as a magnetocaloric material for room temperature magnetic cooling systems.

Effect of La3+ substitution with Gd3+ on the resistive switching properties of La0.7Sr0.3MnO3 thin films

This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in “A” MnO3 perovskite manganite structure. A partial substitution of La3+ in La0.7Sr0.3MnO3 with smaller cation Gd3+ induced A-site vacancy of the largest Sr2+ cation with surface segregation of SrOy due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5 V to 2.5 V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrOy was enhanced with Gd-substitution and the SrOy reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrOy and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

Characteristics and Origin of Sedimentary-Related Manganese Layers in Timor Island, Indonesia

DOI: 10.17014/ijog.v8i4.169Sedimentary-related manganese layers have been discovered in South Central Timor Regency, Timor Island, Indonesia, which is tectonically active and being uplifted due to north-trending tectonic collision between Timor Island arc and Australian continental crust. The manganese layers of 2 to 10 cm-wide interbed with deep sea sedimentary rocks including reddish - reddish brown claystone, radiolarian chert, slate, marl as well as white and pinkish calcilutite of Nakfunu Formations. Stratigraphically, the rock formations are underlain by Bobonaro Formation. Two types of manganese ores found comprise manganese layers and manganese nodule. The manganese layers strongly deformed, lenticular, and segmented, are composed of manganite [MnO(OH)], groutite [MnO(OH)], pyrolusite (MnO2), lithioporite (Al,Li) MnO2(OH)2, and hollandite [Ba (Mn4+, Mn2+)8O16] associated with gangue minerals including calcite, quartz, limonite [FeO(OH)], hematite (Fe2O3), and barite (BaSO4). Whilst the nodule type is only composed of manganite and less limonite. Geochemically, the manganese layers have grade of 63 - 72 wt.% MnO, whereas the nodule one has grade of 63 - 69 wt.% MnO. Generally, iron in Mn ore is very low ranging from 0.2 to 1.54 wt.% Fe2O3, averaged 0.76 wt.%. Hence, Fe/Mn ratio which is very low (0.003 - 0.069), typically indicates a sedimentary origin, which is also supported by petrologic and petrographic data showing layering structure of manganite and lithioporite crystal/grain. Trace element geochemistry indicates that manganese ore was precipitated in a reduction condition. Rare earth element (REE) analysis of manganese ore shows an enrichment of cerium (Ce) suggesting that the ore is basically originated in a marine environment. The manganese nodule is interpreted to be formed by chemical concretion process of unsoluble metals (i.e. mangan, iron) in seawater (hydrogenous) and precipitated on deep sea bottom. On the other hand, the manganese layer is a detrital diagenetic deposit formed by Mn remobilization in seawater column, precipitated and sedimented on the deep sea bottom. Manganese layers have probably been influenced by ‘hydrothermal process’ of mud-volcano activities, proven by the presence of quartz and barite veinlets cutting the Mn layers, manganite recrystallization to be pyrolusite along veinlets cutting manganite and lithioporite layers, and the presence of pyrite and sulphur associated with Mn layers. Field data also exhibit that the significant manganese layers are mostly found around mud volcanoes. The closely spatial and genetic relationships between manganese layers and mud-volcanoes might also be an important guide for the exploration of Mn deposit in the region.

Synthesis, Growth Mechanism and Characterization of MnO(OH) Nano/Micro Structures

The present communication deals with synthesis, characterization and growth mechanism of MnO(OH) nano/micro structures. MnO(OH) structures were synthesized by novel liquid phase pulse laser ablation technique (LP-PLA) in different concentrations of aqueous SDS medium. Synchrotron radiation source was used for X-ray diffraction to investigate structure and phase confirmation of manganite structures. The absorption spectra of colloidal solution of MnO(OH), consists of a narrow band around 242 nm below the critical micelle concentration (CMC) of SDS concentrations (1 and 5 mM), while concentrations (10 and 20 mM) above CMC value, show comparatively broad and less intense absorption. Upon aging, the colloidal particles grow and get assembled to form microspheres and branch micro-rods. Besides the peak observed at 242 nm, absorption band develops two extra broad peaks around 410 and 580 nm. MnO(OH) nano/micro structures, “morphology and particle sizes were studied by TEM/SEM technique. Growth mechanism of the branch micro-rods of MnO(OH) is also discussed. Room temperature electrical transport property of manganite thin film has been studied by I–V characteristics plot.

Study of the transport properties of La0.8Ba0.2MnO3/SrTiO3:Nd heterojunctions under reverse bias

Heterojunctions composed of P-type La0.8Ba0.2MnO3 and N-type Nd doped SrTiO3 are successfully fabricated via chemical solution deposition. Good rectifying property is obtained. Detailed studies of the transport properties under reverse bias show that above the metal-insulator transition temperature TMI, the Frenkel–Poole emission dominates the leakage current and the emission barrier height was extracted. When placed in magnetic field, the junctions show different transport behaviors below and above TMI. It shows negative magnetoresistive effect below TMI and positive one above TMI. This is explained by the phase separation mechanism and the band structure of manganites.

Magnetic exchange interactions and supertransferred hyperfine fields at119Sn probe atoms in CaCu3Mn4O12

The double manganite CaCu${}_{3}$Mn${}_{4}$O${}_{12}$ doped with ${}^{119}$Sn atoms (\ensuremath{\sim}1 at.$%$ with respect to manganese atoms) was studied by use of M\"ossbauer spectroscopy. Formally tetravalent Sn${}^{4+}$ ions substitute for isovalent manganese ions in the octahedral (Mn${}^{4+}$O${}_{6}$) polyhedra. The covalency effects on the magnetic interactions like superexchange in Cu${}^{2+}$-O-Mn${}^{4+}$ and Mn${}^{4+}$-O-Mn${}^{4+}$ bonds and supertransferred hyperfine interactions of the ${}^{119}$Sn probe atoms in the manganite structure are discussed. Using a semiquantitative nearest-neighbor cluster model relating the hyperfine magnetic field on the ${}^{119}$Sn nuclei (${H}_{\mathrm{Sn}}$ $=$ 105 kOe at $T$ $=$ 77 K) to covalency parameters and angle characterizing the Sn-O-$M$ ($M$ $=$ Cu, Mn) bonds, it has been shown how such an analysis of supertransferred hyperfine interactions of tin probe ions can get fruitful information about strength and sign of the superexchange interactions between Mn${}^{4+}$ and Cu${}^{2+}$ magnetic ions. A consistent description of the results in the framework of the Weiss molecular field model considering the specific local environment of tin atoms has made it possible to estimate exchange integrals: ${J}_{\mathrm{CuMn}}$ $=$ \ensuremath{-}51.1 \ifmmode\pm\else\textpm\fi{} 0.3 K and ${J}_{\mathrm{MnMn}}$ $=$ \ensuremath{-}0.6 \ifmmode\pm\else\textpm\fi{} 0.2 K.

Theoretical investigation of NMR spectra in rare-earth manganites

The work is aimed to theoretical investigation of orbital and magnetic structure of manganites. The orbitally-dependent exchange interaction model was used in order to describe the superexchange interaction in all range of RMnO3 (R = La, Pr, Nd, Tb, Dy, Ho) orfhorhombic compounds. The model of nearest-neighbour and next-nearest neighbour exchange was used to describe the magnetic structures of manganites with small rare-earth ion sublattice (R = Dy, Tb, Ho). We investigate different types −A, E, non-collinear - of magnetic structures. The models of NMR spectra calculation of Mn3+ ion in RMnO3 compounds are proposed. The theoretical study of the magnetic structure could distinguish The NMR-spectra of antiferromagnetic (A or E) or strongly non-collinear ordering type.

57Fe and 119Sn probe Mössbauer spectroscopy investigation of perovskite-type double manganite family CaCu x Mn7−x O12 (x = 0, 0.15, 3)

CaCuxMn7−xO12 (x = 0, 0.15, 3) manganites were studied by 57Fe and 119Sn probe Mossbauer spectroscopy. It was established that the 57Fe and 119Sn probe cations are stabilized in the octahedral positions of the manganite structures by substituting the manganese cations. The magnetic and structure phase transition temperatures of CaMn7O12 and CaCu0.15Mn6.85O12 manganites fell upon the introduction of 57Fe probe cations into their structures. It was concluded that intrasublattice Mn4+-O-Mn4+ exchange interactions play a noticeable role in the formation of the magnetic structure of CaCu3Mn4O12 manganite.

The Effect of Hydrostatic Pressure on Crystal and Orbital Structures of LaMnO<sub>3</sub> and LaMn<sub>0.5</sub>Ga<sub>0.5</sub>O<sub>3</sub>

The crystal structure of manganite under pressure is investigated. The influence of external hydrostatical pressure is studied. The theoretical study of magnetic interactions and NMR spectra under pressure is carried out. The influence of Ga-doping is discussed.

Anisotropic magnetoresistance in manganites: experiment and theory

We present measurements of the anisotropic magnetoresistance (AMR) ofLa0.75Sr0.25MnO3 films depositedon (001) SrTiO3 substrates, and a model that describes the experimental results. The model,based on the electronic structure of manganites plus the spin–orbit coupling,correctly accounts for the dependence of the AMR on the direction ofthe current to the crystalline axes. We measure an AMR of the order of10 − 3 for thecurrent I parallel to the [100] axis of the crystal and vanishing AMR for , in agreement with the model predictions. Further, we calculate the planar Hall effect andshow its connection to AMR.

High pressure behavior of Ga-doped LaMnO3: a combined X-ray diffraction and optical spectroscopy study

The pressure effects on the Jahn–Teller (JT) distortion of three representative compounds belonging to the LaMn1−xGaxO3 (x = 0.2, 0.3, 0.4) family were widely investigated by means of X-ray diffraction and Raman spectroscopy. A compound with a fully coherent JT distorted structure (x = 0.2), one with regular octahedra (x = 0.6) and one in an intermediate configuration (x = 0.3) were selected. A pressure induced transition from the orthorhombic Pbnm phase towards structures with higher symmetry was observed in all the samples. Both Raman and X-ray data confirm that the most important structural effect of pressure is that of reducing the octahedral distortion. The appearance of a feature in the lattice parameter behavior connected to a structural instability was also detected, pointing out the key role of the JT distortion in stabilizing the manganite structures. On the other hand, the complete suppression of the JT distortion in the high-pressure phases cannot be claimed. The Raman spectra collected on the more distorted compounds (x = 0.2, 0.3) reveal clearly the coexistence of domains of distorted and more regular octahedra in a certain pressure range. The first sketch of the pressure vs. Ga-content phase diagram was drawn.

Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn–Teller transitions in ABX 3 perovskites. I. Theory

Space groups, order-parameter and strain/order-parameter coupling relationships in ABX3 perovskite structures which combine cooperative Jahn-Teller distortions and octahedral tilting have been investigated from the perspective of group theory using the computer program ISOTROPY. Two common Jahn-Teller ordering schemes are associated with the irreducible representations M2+ and R3+ of the space group Pm3m. A third, less-common ordering scheme is associated with Gamma3+. These combine with tilting instabilities associated with M3+ and R4+ to generate a predicted suite of Jahn-Teller structure types that includes many of the known structures of manganites, vanadates, Cu and Cr halides. Order-parameter coupling and possible phase transitions are described using Landau free-energy expansions, and general expressions for the relationships between symmetry-adapted spontaneous strains and particular order-parameter components are presented. These provide a general formal framework for determining structural evolution across multi-component order-parameter space and for characterizing the influence of tilting instabilities on Jahn-Teller instabilities or of Jahn-Teller ordering on octahedral tilting.

Current-driven channel switching and colossal positive magnetoresistance in the manganite-based structure

The transport and magnetotransport properties of a newly fabricated tunnel structure manganite/depletion layer/manganese silicide have been studied in the current-in-plane (CIP) geometry. A manganite depletion layer in the structure forms a potential barrier sandwiched between two conducting layers, one of manganite and the other of manganese silicide. The voltage–current characteristics of the structure are nonlinear due to switching conducting channels from an upper manganite film to a bottom, more conductive MnSi layer with an increase in the current applied to the structure. Bias current assists tunnelling of a carrier across the depletion layer; thus, a low-resistance contact between the current-carrying electrodes and the bottom layer is established. Below 30 K, both conducting layers are in the ferromagnetic state (magnetic tunnel junction), which allows control of the resistance of the tunnel junction and, consequently, switching of the conducting channels by the magnetic field. This provides a fundamentally new mechanism of magnetoresistance (MR) implementation in the magnetic layered structure with CIP geometry. MR of the structure under study depends on the bias current and can reach values greater than 400% in a magnetic field lower than 1 kOe. A positive MR value is related to peculiarities of the spin-polarized electronic structures of manganites and manganese silicides.