Perovskite Manganite La0 Research Articles

Highly Recyclable and Versatile La0.5Nd0.2Ca0.3MnO3 and La0.5Nd0.2Ca0.25K0.05MnO3 Perovskite Catalysts for Effective Removal of Organic Contaminants

AbstractWastewater contamination, particularly from dye effluents containing organic colorants originating from industrial sources, represents a significant environmental and public health hazard. This study is dedicated to removal of these abundant coloured effluents in wastewater, addressing the imperative need for effective remediation strategies to safeguard ecosystems and human well‐being. In this regard, bare and K‐doped perovskite manganites La0.5Nd0.2Ca0.3MnO3 (LCM) and La0.5Nd0.2Ca0.25K0.05MnO3 (LCKM) nanoparticles respectively were synthesized in order to study their catalytic behaviour for degradation of coloured effluents. The Rietveld analysis applied to the X‐ray diffraction data provides confirmation of orthorhombic symmetry. For exploring the catalytic properties, rhodamine‐B (RhB) dye was chosen as model dye pollutant. The achieved degradation efficiency is substantial, reaching 99 % within a brief period of 10–12 min. Following these results, we have also carried out the degradation of some other dyes such as methylene blue (MB) and methyl orange (MO). It was observed that MO dye was more efficiently degraded in quick time as compared to all the other dyes due to its anionic nature. Furthermore, the comparative catalytic efficiencies of LCM and LCKM catalysts were explained on the basis of Mn3+/Mn4+ redox pairs and it was observed that LCKM had shown better degradation efficiency than LCM.

Synthesis and magnetic properties of perovskite manganite La0.8Ca0.15Na0.05Mn0.8Fe0.2O3

Synthesis and magnetic properties of perovskite manganite La0.8Ca0.15Na0.05Mn0.8Fe0.2O3

Variation of local magnetism in a perovskite manganite La0.7Ca0.3MnO3 by Fe doping

Variation of local magnetism in a perovskite manganite La0.7Ca0.3MnO3 by Fe doping

Mild nitridation of perovskite manganite: Synthesis, structure and magnetism

The nitrogen lightly doped perovskite manganite La0.5Ba0.5MnO(3-δ)-xNx was synthesized following a mild nitridation strategy by optimizing annealing temperature, annealing time and NH3/Ar flow rate ratio. Neutron powder diffraction (NPD) characterization evidences an N-doping triggered structural phase transition from pseudo-cubic Pm-3m to tetragonal P4/mmm and further confirms a preferable substitution at O1 and O2 sites closing to the Ba-rich layers. N 1s K-edge X-ray absorption near edge spectrum (XANES) with total fluorescence yield (TFY) mode, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy collectively convince the Mn–N bonded state. The O/N atomic ratio is determined to be 2.26/0.22 by XPS analysis closing to the value of 2.25/0.18 from NPD refinement. Magnetic property characterization reveals that both long-range Mn3+-O-Mn4+ ferromagnetic coupling and high Curie temperature (TC) are maintained upon N-doping. Besides, significant spin frozen with robust domain pinning is identified below TC which can be ascribed to the short-range Mn–N–Mn clusters and/or oxygen defects. This work expands the connotation of transition-metal based perovskite oxynitride and may inspire the development of photosensitive semiconductor device with magnetic response.

Magnetic Entropy Change and Lattice Potential Energy in Perovskite Manganites La0.6Pr0.1Ba0.3MnO3

Magnetic Entropy Change and Lattice Potential Energy in Perovskite Manganites La0.6Pr0.1Ba0.3MnO3

Enhancement in the Electrochemical Performance of Strontium (Sr)-Doped LaMnO3 as Supercapacitor Materials

In this study, Strontium (Sr)-doped perovskite lanthanum manganite (La1−xSrxMnO3) nanoparticles were prepared by the sol–gel method and used as electrode materials of supercapacitors. Microstructures, morphologies, and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), a transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) surface area measurements, cyclic voltammetry (CV), and galvanostatic charge/discharge (GCD) cycling. Investigations demonstrated that the La0.85Sr0.15MnO3 nanoparticles had a maximum specific capacitance of 185.5 F/g at a current density of 0.5 A/g and a low charge transfer resistance (0.38 Ω) in 3 M KOH aqueous electrolyte solutions. La0.85Sr0.15MnO3 electrode yields the highest capacitance behavior because of the larger specific surface area, lower charge transfer resistance, and higher concentration of oxygen vacancy. This result demonstrates that Sr doping significantly improved the electrochemical properties of the LaMnO3 system. The anion-intercalation mechanism was examined by a charge–discharge process. This provides a promising electrode material for supercapacitors.

Magnetic properties and critical behavior of the perovskite manganite La0.825Sr0.175MnO3

Polycrystalline La0.825Sr0.175MnO3 was prepared by solid state reaction method. It exhibits a ferromagnetic–paramagnetic phase transition at TC∼286 K. The intrinsic magnetic properties were clarified by the scaling theory and the isothermal magnetization measured around TC. Based on the modified Arrott plot, Kouvel–Fisher method and Widom relation, the critical exponents are determined to be β=0.308(7), γ=1.065(8), δ=4.457(17). Normalization of the critical exponents shows that the extended exchange interaction decays with J∼r−4.861, consistent with Tricritical mean field model. Rhodes–Wohlfarth ratio PC/MS>1 suggests that La0.825Sr0.175MnO3 is completely itinerant ferromagnet.

Silver addition in polycrystalline La0.7Ca0.3MnO3: Large magnetoresistance and anisotropic magnetoresistance for manganite sensors

Perovskite manganite La1−yCayMnO3 has giant and tunable magnetoresistance (MR) and anisotropic magnetoresistance (AMR), still the following two challenges are of great concern: (i) large magnetic field is required for achieving excellent electromagnetic performance; and (ii) metal–insulator (M–I) transition temperature (TMI) significantly different from room temperature; both these factors limit its practical applications. In this study, polycrystalline La0.7Ca0.3MnO3:Agx composites were fabricated by sol–gel and solid–phase addition methods, and large MR and AMR (84.1% and 32%, respectively) were obtained at near room temperature in 1 T magnetic field when x = 0.2. Evidently, it was found that the grain boundary scattering effects were weakened due to Ag−addition, which resulted in an enhancement of MR. The tremendously high AMR value was attributed to the anisotropic spin–orbit coupling (SOC) effect. The electron–scattering and small–polaron hopping models were used to successfully fit the resistivity data, which support the SOC effect under different magnetic fields that enhance the AMR. These results support further development of the perovskite manganese oxide with potential applications in manganite devices.

A study of structural, magnetic and magnetocaloric properties of (1−x)La0.6Ca0.4MnO3/xMn2O3 composite materials

Perovskite manganite (1−x)La0.6Ca0.4MnO3/xMn2O3 (x = 0, 0.05. 0.1, 0.15, 0.20) composites were prepared by solid state reaction method. X-ray diffraction measurements were used to confirm the crystal structure and the average crystallite size of the samples. Their magnetic, magnetocaloric and heat capacity properties display a presence of second order magnetic phase transition at 260 K. The maximum magnetic entropy change was found to be 5.33 J/kgK for x = 0.1 of Mn2O3 under 5 T. The relative cooling power (RCP) was found (235 J/kg) to largely exceed that reported in early works for a similar family of materials. In addition, the RCP of the mother alloy is enhanced by more than 20% under 32 kOe without affecting the Curie temperature that remains approximately constant close to 260 K. Our results suggest that the addition of Mn2O3 could be useful for the enhancement of the LCMO refrigerant capacity without affecting the Curie temperature.

Magnetic property under the pressure and electrical transport behavior under the magnetic field for the perovskite manganite La0.7Ca0.3MnO3

Abstract With respect to the magnetic properties under the pressure for the ferromagnetic metallic system La1−xCaxMnO3(0.18 ≤x

Correlation between magnetic and transport properties of rare earth doped perovskite manganites La0.6R0.1Ca0.3MnO3 (R = La, Nd, Sm, Gd, and Dy) synthesized by Pechini process

Here, we report a comparative study of rare earth doped La0.6R0.1Ca0.3MnO3 (R = La, Nd, Sm, Gd, and Dy) samples synthesized by sol-gel Pechini process. All the compounds are single-phased and crystallize in Pbnm space group with orthorhombic symmetry. Temperature dependent magnetization measurements revealed that all our compounds exhibit a paramagnetic (PM)–ferromagnetic (FM) transition with decrease in both ordering temperature TC and the freezing temperature TF with decrease in ionic radii of lanthanide ions. The compounds display metal-semiconductor transition and the temperatures (TMS) obtained from the electrical resistivity measurements are consistently higher than those of the Curie temperatures TC. The transport properties are dominated by the Variable-range hopping (VRH) model above TMS, showing an increase in characteristic VRH temperature with decreasing size of rare-earth ion. The estimated hopping distance (RH) in all the samples is close to nearest neighbor Mn–O–Mn distance (~5 Å) in the ab plane.

Unambiguous determining the Curie point in perovskite manganite with second-order phase transition by scaling method

The accurate determination of the Curie temperature (TC) is particularly important in describing the magnetic behavior close to the paramagnetic-ferromagnetic (PM-FM) phase transition. In this paper, we studied the magnetic phase transition and accurately predicted the Curie point of perovskite manganite La0.825Sr0.175MnO3. We find the compound shows a second-order PM-FM transition and has a large magnetic entropy change (MEC) in vicinity of phase transition region. Based on the scaling law and the correlation between magnetic field and MEC, the precise and magnetic-independent Curie temperature was determined to be 281.7 K, obviously lower than 285.4 K decided from the magnetization versus temperature. The reliability of new Curie temperature can be well confirmed by the modified Arrott plot together with the critical exponents. Our results not only open up a new pathway for precise definition of Curie point but also facilitate the efficient exploitation of spontaneous magnetic bubbles in perovskite manganite.

Electrical Transport Property and Electron Paramagnetic Resonance Research of a Perovskite Manganite

Unique electrical transport properties of double metal-insulator transitions were found in perovskite manganite La0.6Pr0.1Ba0.3MnO3 prepared using the sol-gel method. The relevant electron paramagnetic resonance characteristics were investigated. The ferromagnetic and paramagnetic phase transition temperatures were determined by the magnetisation vs temperature M-T curves. The unique electrical transport properties originated from the coexistence of metal and insulator, ferromagnetic, and paramagnetic components in a given temperature range.

Magnetic properties and magnetic entropy change of perovskite manganites La0.9–xEuxSr0.1MnO3 (x=0.000, 0.075) by experimental method and numerical fitting

Polycrystalline samples La0.9-xEuxSr0.1MnO3 (x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism (FM) characteristic in the temperature range of 15–125 K and 15–150 K respectively; the samples show preformed clusters in the temperature range of 125–343 K and 150–325 K, respectively, the samples show paramagnetism (PM) characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |ΔSM| value of the samples is near the Curie temperature (TC), and the value of |ΔSM| reaches 2.76 and 3.03 J/(K·kg), respectively. In addition, the relative cooling power (RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region (T > 77 K).

Robust electronic phase separation on nanoscale of perovskite manganite La0.825Sr0.175MnO3

Electronic phase separation (EPS) plays a key role in elucidating the effects of complexity on emergent behavior for correlated electronic materials. In this work, we thoroughly studied a robust EPS existed in perovskite manganite La0.825Sr0.175MnO3. Results show that a typical paramagnetic-ferromagnetic (PM-FM) phase transition and a metallic-insulating phase transition occur at 285.4 and 295 K, respectively. Electron paramagnetic resonance (EPR) spectroscopy confirms that there are a double peaks rather than a single peak structures in the temperature region of 290 K≤T≤315 K, indicating that an obvious EPS state generates in this compound. Based on the variation of EPR intensities, we found that the FM composition continues to increase with the decrease of temperature in the whole EPS region. Moreover, it causes a percolative-like metallic-insulting transition when the percolative threshold approach ∼22.63% which is nearly equivalent to 25.34% obtained by calculating the ratio of spontaneous magnetization against theoretical saturated magnetization. Detailed phase diagram shows that the EPS state not only occupies most of PM region but also a state of multiphase coexistence is also found.

Hidden metal-insulator transition in manganites synthesized via a controllable oxidation

Oxygen usually plays crucial roles in tuning the phase structures and functionalities of complex oxides such as high temperature superconductivity, colossal magnetoresistance, catalysis, etc. Effective and considerable control of the oxygen content in those functional oxides could be highly desired. Here, using perovskite manganite (La0.5Sr0.5)MnO3 as a paradigm, we develop a new pathway to synthesize the epitaxial thin films assisted by an in-situ chemical process, where the oxygen content can be precisely controlled by varying oxidative activity tuned by the atmospheric temperature (Tatm) during the growth. A hidden metal-insulator transition (MIT) emerges due to the phase competition, which is never shown in the phase diagram of this classic manganite. The oxygen-mediated interaction between Mn ions together with the change of carrier density might be responsible for this emerging phase, which is compatible with the results of first-principle calculations. This work demonstrates that, apart from traditional cation doping, a precise modulation of anion (O2−, S2−, etc.) may provide a new strategy to control phase structures and functionalities of epitaxial compound thin films.

Why typical magnetic metals and oxides have different Curie temperatures

Why do typical magnetic metals and oxides have different Curie temperatures (TC)? For example, TC = 1404, 1043, and 631 K for Co, Fe, and Ni, respectively; and TC = 860 and 369 K for spinel ferrite Fe3O4 and perovskite manganite La0.7Sr0.3MnO3, respectively. Until now, no satisfactory explanation for this magnetic ordering puzzle has been found although Weiss proposed the molecular field assumption for magnetic ordering in 1907. In this letter, we propose an explanation for this puzzle using a Weiss electron pair model based on atomic physics theory.

Coexistence of spin-lattice and spin-spin relaxation mechanism in perovskite manganite (La0.5Pr0.5)0.67Ca0.33MnO3

Electron paramagnetic resonance (EPR) was applied extensively to probe the phase separation and spin relaxation mechanism in the perovskite manganites. In this study, we conducted the measurement of EPR for the perovskite manganites (La0.5Pr0.5)0.67Ca0.33MnO3. We found that both paramagnetic and ferromagnetic resonance peaks simultaneously emerged on resonance spectrum near below TC, exhibiting a typical characteristic of phase separation. The linewidth of EPR spectrum progressively enlarged upon the rising of temperature in the temperature range of T>TC and a quasilinear variation of peak-peak width was observed at TC<T<500 K. In contrast to the usual beliefs that the variation of peak-peak linewidth can be understood either by spin-lattice relaxation or by spin-spin relaxation, however, the linewidth behavior observed here shows a coexistence of two spin relaxation mechanisms. We proposed that the inhomogeneous electronic phases due to the intrinsic self-organizing growth were responsible for the appearance of multiple spin exchange interactions and variational relaxation mechanism. This finding would be possible to pave a new way for further investigating magnetic correlations and spin dynamics in the paramagnetic hole-doped manganites.

Structural, magnetic, and magnetocaloric properties of bilayer manganite La1.38Sr1.62Mn2O7

In this study, we investigated the structural, magnetic phase transition, and magnetocaloric properties of bilayer perovskite manganite La1.38Sr1.62Mn2O7 based on X-ray diffraction, electron paramagnetic resonance, and temperature-/magnetic field-dependent magnetization measurements. The structural characterization results showed the prepared sample had a tetragonal structure with the space group I4/mmm. The Curie temperature was determined as 114 K in the magnetization studies and a second-order paramagnetic-ferromagnetic transition was confirmed by the Arrott plot, which showed that the slopes were positive for all the curves. According to the variation in the electron paramagnetic resonance spectrum, we detected obvious electronic phase separation across a broad temperature range from 220 to 80 K in this magnetic material, thereby indicating that the paramagnetic and ferromagnetic phases coexist above as well as below the Curie temperature. Based on a plot of the isothermal magnetization versus the magnetic applied field, we deduced the maximum magnetic entropy change, which only reached 1.89 J/kg.K under an applied magnetic field of 7.0 T. These theoretical investigations indicated that in addition to the magnetoelastic couplings and electron interaction, electronic phase separation and anisotropic exchange interactions also affect the magnetic entropy changes in this bilayer manganite.

Infrared properties of perovskite manganites La1−xCaxMnO3 with 0.25 ≤ x ≤ 0.45

The systematical investigations of infrared phonon spectra were performed on the perovskite manganites La1−xCaxMnO3 with 0.25 ≤ x ≤ 0.45. Both frequency shift of stretching mode and effective number of carriers neff∗(T) change dramatically near the Curie temperature for all compounds. Moreover, Ca concentration dependences of variations of the phonon frequencies and neff∗(T) shows their extreme values around x = 0.35 and 0.40 respectively at the measuring temperatures. With the varying Ca concentration, the competition between the strong Jahn-Teller coupling and the magnetic double exchange interaction may be responsible for those results.