Manganite Oxides Research Articles

Mn-deficient ZnMn2O4/Zn0.5Mn0.5Fe2O4 cathode for enhancing structural reversibility and stability of zinc-ion batteries

Aqueous zinc-ion batteries have surfaced as a viable energy storage technology due to their safety, eco-friendliness, and cost-effectiveness. Binary zinc manganite oxide (ZnMn2O4 or ZMO) stands out as the potential cathode material owing to its considerable theoretical capacity and high operating voltage. However, high electrostatic repulsion of Zn2+ ions within ZMO leads to sluggish diffusion and poor reversibility of Zn2+ ions insertion/extraction that can reduce charge storage and overall cycling performance. This study addresses this challenge by introducing FeCl3 during the synthesis to form ZMO/Zn0.5Mn0.5Fe2O4 (ZMFO) cathode material. This cathode features Mn-deficient structures, which can reduce the electrostatic repulsion via low Mn occupancies and lattice parameters enlargement, thus facilitating Zn2+ ions diffusion. Ex-situ X-ray diffraction analyses further show that the cathode is able to maintain good structural reversibility during the charge-discharge cycles. Additionally, the ZMO/ZMFO cathode exhibits smaller particle sizes than pristine ZMO, providing a wider surface area. The presence of ZMFO with a large unit cell volume can also enhance Zn storage capacity and accelerate Zn2+ ions kinetics. Highlighting those advantages, aqueous zinc-ion batteries with ZMO/ZMFO cathode show a capacity of ~230 mAh g−1 at 0.05 A g−1 and retain 99 % of its initial capacity at 0.2 A g−1 after 200 cycles of charge-discharge.

Strained single crystal high entropy oxide manganite thin films

The ability to accommodate multiple principal cations within a single crystallographic structure makes high entropy oxides (HEOs) ideal systems for exploring new composition–property relationships. In this work, the high-entropy design strategy is extended to strained single-crystal HEO-manganite (HEO-Mn) thin films. Phase-pure orthorhombic films of (Gd0.2La0.2Nd0.2Sm0.2Sr0.2)MnO3 were deposited on three different single-crystal substrates: SrTiO3 (STO) (100), NdGaO3 (110), and LaAlO3 (LAO) (100), each inducing different degrees of epitaxial strain. Fully coherent growth of the thin films is observed in all cases, despite the high degree of lattice mismatch between HEO-Mn and LAO. Magnetometry measurements reveal distinct differences in the magnetic properties between epitaxially strained HEO-Mn thin films and their bulk crystalline HEO counterparts. In particular, the bulk polycrystalline HEO-Mn shows two magnetic transitions as opposed to a single one observed in epitaxial thin films. Moreover, the HEO-Mn film deposited on LAO exhibits a significant reduction in the Curie temperature, which is attributed to the strong variation of the in-plane lattice parameter along the thickness of the film and the resulting changes in the Mn–O–Mn bond geometry. Thus, this preliminary study demonstrates the potential of combining high entropy design with strain engineering to tailor the structure and functionality of perovskite manganites.

Fabrication and characterization of suspended La0.7Sr0.3MnO3 nanofibers for high-sensitive and fast-responsive infrared bolometer

La1−x Sr x MnO3 manganite oxides have shown great potential for infrared (IR) sensing. In this study, La0.7Sr0.3MnO3 (LSMO) nanofibers, synthesized by a simple electrospinning process, are suspended between gold interdigitated electrode (IDE). These electrodes, which acts as a supporting platform for the dangling nanofiber, are microelectromechanical systems based that can be fabricated quickly and economically with fewer fabrication steps. Due to the large surface-area-to-volume ratio, these fibers have outstanding thermo-electrical properties, which puts them in the leagues of materials suitable for IR sensing. Performance-wise these hanging nanofibers belong to a class of promising thermal sensors due to negligible thermal loss. The optoelectrical characterization shows its temperature coefficient of resistance (TCR) is −1.48%K−1, and its electrical resistance follows an inverse square law for distance from the IR source. The fabricated LSMO nanofibers based microbolometer has a significantly low thermal time constant with average thermal response and recovery time of 63 ms and 77 ms, respectively. Furthermore, they show encouraging bolometric properties with thermal conductance, thermal capacitance, voltage responsivity, and thermal noise limited detectivity of 3.6 × 10−3WK−1, 0.2268 × 10−3JK−1 , 1.96 × 105VW−1, and 3.7 × 108cm Hz1/2W−1 respectively. The high voltage responsivity and TCR, commensurate with the ultralow response and recovery time confirm that the fabricated Microbolometer can find industrial applications as thermal sensors.

Microwave-aided fabrication of calcium-substituted DyMnO3 nanocomposites as prospective battery-type electrode material for supercapacitors

The Multifaceted properties of nanostructured rare earth perovskite manganite oxides have attracted much attention specifically for their applications in energy storage systems. In the present work, synthesis and physiochemical properties of calcium-substituted dysprosium perovskite manganite oxide nanocomposites and their potential applications as supercapacitors are examined. The perovskite structure and morphology of the designed nanocomposites are affirmed by the different analytical tools, including XRD, SEM, and TEM analysis. The structural analysis by XRD indicates the presence of DyMnO3 perovskite phase with additional peaks of Dy2O3 phase. The percentage of Dy2O3 is gradually reduced with higher Ca substitution, from about 16% to 7%. The Halder-Wagner method indicates an increase of the microstrain and a decrease in crystallite size with the rise of Ca substitution. From Tauc’s plot derived from DRS analysis, a slight increase in the band gap with the increase in Ca substitution is observed (2.55–2.62 eV). The surface elemental compositions and the valence states of individual elements analyzed using XPS analysis evidence the presence of Dy, Ca, Mn, and O. BET adsorption study indicates an increase in pore size, surface area, and pore volume with increasing Ca substitution concentration. When employed as a supercapacitor electrode material, Calcium-blend DyMnO3 nanocompositeexhibits battery type behavior. This material shows a higher specific capacitance (capacity) of 531 Fg−1 (319.9 Cg−1) with comparatively low charge transfer resistance and better cyclic stability. We have assembled an asymmetric supercapacitor device using our prepared sample exhibiting energy density of 36.16 Wh/kg with better cyclic stability. This work provides new insights for designing future Dy2O3 based supercapacitors.

Face mask integrated with flexible and wearable manganite oxide respiration sensor

Face masks are key personal protective equipment for reducing exposure to viruses and other environmental hazards such as air pollution. Integrating flexible and wearable sensors into face masks can provide valuable insights into personal and public health. The advantages that a breath-monitoring face mask requires, including multi-functional sensing ability and continuous, long-term dynamic breathing process monitoring, have been underdeveloped to date. Here, we design an effective human breath monitoring face mask based on a flexible La0.7Sr0.3MnO3 (LSMO)/Mica respiration sensor. The sensor’s capabilities and systematic measurements are investigated under two application scenes, namely clinical monitoring mode and daily monitoring mode, to monitor, recognise, and analyse different human breath status, i.e., cough, normal breath, and deep breath. This sensing system exhibits super-stability and multi-modal capabilities in continuous and long-time monitoring of the human breath. We determine that during monitoring human breath, thermal diffusion in LSMO is responsible for the change of resistance in flexible LSMO/Mica sensor. Both simulated and experimental results demonstrate good discernibility of the flexible LSMO/Mica sensor operating at different breath status. Our work opens a route for the design of novel flexible and wearable electronic devices.

Structural, AC conductivity, dielectric and impedance studies of polypyrrole/praseodymium calcium manganite nanocomposites

In-situ polymerization of a series of nanocomposites viz. 10, 20, 30, 40 and 50 wt % of Praseodymium Calcium Manganite Oxide (Pr0.75Ca0.25MnO3) (PCM) nano manganites in polypyrrole (PPy) were prepared by chemical polymerization technique. The crystalline nature of all the nanocomposites was confirmed by powder X-ray diffraction (XRD). The orthorhombic structure with space group Pnma was confirmed by the well-fitted Rietveld refined XRD data. The average particle size was observed to be in the range of 42 to 60 nm. Scanning Electron Microscope (SEM) confirmed the spherical nature of the particles. The TEM confirmed the crystallinity and Fourier Transform Infra-Red Spectroscopy (FTIR) showed that the stretching frequencies shifted towards higher frequencies for the nanocomposites suggesting better conjugation due to chemical interaction between the PPy and PCM particles. AC conductivity versus frequency showed that at higher frequencies the AC increases obeying Jonscher’s power law. The correlated barrier hopping (CBH) model is therefore used to describe the conduction mechanism. For all composites, the dielectric constant and tangent loss revealed a frequency- and temperaturedependent character. The real and imaginary impedance were both frequency and temperature dependent. The impedance data were analyzed by fitting Nyquist plots using ZsimpWin software which confirmed non Debye type of behavior. This study highlights on the interactions between conduction processes, grain boundaries, and grains.

Rational Development of IT-SOFC Electrodes Based on the Nanofunctionalization of La0.6Sr0.4Ga0.3Fe0.7O3 with Oxides. Part 2: Anodes by Means of Manganite Oxide.

To promote the diffusion on the market of solid oxide fuel cell (SOFC) devices, the use of fuels other than the most appealing hydrogen and also decreasing the working temperature could show the way forward. In the first part, we concentrated our efforts on cathodes; hereby, we focused on anodes and concentrated our efforts to develop a sustainable multifuel anode. We decided to develop LSGF (La0.6Sr0.4Ga0.3Fe0.7O3)-based nanocomposites by depositing manganite oxide to enhance the performance toward propane. MnOx has been deposited by a wet impregnation method, and the powders have been largely characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, oxygen temperature-programmed desorption, and N2 adsorption. Cell performances were first collected in hydrogen as a function of both the temperature and hydrogen content. EIS measurements were studied using Nyquist and Bode plots, and they show two processes at high frequency, assigned to charge transfer at the electrode/electrolyte interface, and at low frequency due to the dissociative adsorption of hydrogen. The Arrhenius plot of area specific resistance suggests two different trends, and the activation energy decreases from 117 kJ/mol at 750 °C to 46 kJ/mol above that temperature. This behavior is often connected to chemical modification of the catalyst or changes in the limiting step processes. Power densities in hydrogen and propane were determined at 744 °C after 1 h of operation, achieving 70 mW/cm2 in H2 and 67 mW/cm2 in C3H8. The open-circuit voltage increases from 1.10 V in hydrogen to 1.13 V in propane.

The structural and magnetic features of perovskite oxides La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) depending on the strontium doping content and heat treatment

Sr-doped (0<x < 0.2) ceramic samples of the lanthanum manganite oxides were obtained via sol-gel method to investigate the influence of doping on structural, magnetic end electronic responses, and their correlations. Synthesized samples of non-stoichiometric compositions are rhombohedral single-phase. After annealing the formation of a phase-separated system as a mixture of orthorhombic phases was found. The R-3c and PnmaI, PnmaII* and PnmaII phases have been studied using Mössbauer spectroscopy, XRD, SEM analysis and magnetic measurements. The magnetic temperature-concentration phase diagram of La1–xSrxMnO3+δ (x = 0.05, 0.10, 0.20) was obtained.The Jahn-Teller effect or the orbital order breaking, as well as the competition between Mn3+–O2—Mn4+ double- and Mn3+–O2-–Mn3+ superexchange interaction was demonstrated under the effect of cation doping compound and interstitial oxygen value (δ). The relaxation character of the Mössbauer spectra and the type of magnetization dependences revealed nanosized magnetic clusters with fluctuation of their magnetic moment in all perovskite phases. Results are interpreted in terms of matrix – clusters: regions of sample with ferromagnetic type of ordering (cluster) exist in antiferromagnetically or ferromagnetically (with different exchange parameter) ordered matrix. Exchange interaction frustrations of the cluster with the matrix can lead to relaxation behavior of the magnetic moment of the cluster. The clusters size vary from about 3.9 to 5.7 nm. All samples are characterized by the presence of particles agglometates with a typical size about 0.4–0.8 μm; for annealed samples additional non-conducting regions with 80–220 nm in size were found. It is shown that the annealing time significantly affects the production of materials with determined properties and be useful in the applied field in technological processes.

Superflexibility in single-crystalline manganite oxide membranes with gigantic bending curvature and strain

High-quality flexible membranes have promoted a myriad of applications in soft electronics or spintronic devices. Nevertheless, magnetic membranes that can withstand strong folding and rolling distortions have rarely been reported. Here, we found that the few to tens of nanometer thick LaMnO3 membranes with single-crystalline qualities exhibit superflexibility, demonstrated by self-folding and rolling into few-micron and sub-micron features. The combined scanning transmission electron microscope and selected area electron diffraction experiments simultaneously confirm the 180° folded single crystalline structure and the associated bending curvature and strain as large as 2 μm−1 and 4%. Furthermore, the scanning electron microscope revealed that as the membrane thickness decreases from 40 to 20 nm and 8 nm, the 180° folding is replaced by self-rolling into few-micron size tubes. Magnetization measurements revealed a large saturation (remnant) magnetization enhancement of 21% (34%) achieved in a macroscopically forced bending state under a similar bending strain of 4.9%. This work demonstrates the superflexibility of manganite oxide membranes which promise superior potential in flexible magnetic device applications.

Magnetic performance of amorphous manganese nanoparticles doped with rare earth elements

We studied magnetic and magnetocaloric response in nanoparticle manganite oxides (ABO3-type manganese oxides), which were chemically prepared by sol–gel method with different composition RMnO3 (R = Gd, Tb, Ce) (GMO, TMO, CMO). The structural characterization was performed by EDX (Energy-dispersive X-ray spectroscopy) technique, using TEM (Transmission electron microscopy) methods and XRD and confirmed the nanosized character and morphology of studied manganites. Despite the amorphous character of the samples RMnO3 (R = Gd, Tb), the relatively large magnetic entropy change − ΔSM(7 K) ∼15 J/kgK and − ΔSM (13 K) ∼8 J/kgK has been observed in the case of GMO and TMO, respectively. Sample CMO, despite of its crystalline character, exhibits the lowest magnetic entropy change and the magnetic properties are affected by Jahn-Teller distortion in Mn3O4 nanoparticles (NPs). All systems GMO, TMO, CMO exhibit the Arrott plots with linear behavior and positive slopes that is according to the Banerjee criterion a signature of the second order phase transition. This is in line with our conclusions on the presence of AFM-PM phase transitions in the systems that we drew from ZFC-FC data. Our results confirm that also amorphous manganites especially with Gd show feasible properties for potential magnetic refrigeration applications.

Flexible La0.67Sr0.33MnO3:ZnO Nanocomposite Thin Films Integrated on Mica

The integration of functional oxide thin films on flexible substrates is critical for their application in flexible electronics. Here, to achieve flexible perovskite manganite oxide film with excellent low-field magnetoresistance (LFMR) effect, textured La0.67Sr0.33MnO3 (LSMO):ZnO nanocomposite film was deposited on a flexible mica substrate with ZnO buffer using pulsed laser deposition (PLD). Compared to the polycrystalline LSMO:ZnO nanocomposite film directly deposited on mica without buffer, the LSMO:ZnO/ZnO/mica sample exhibits larger saturation magnetization (164 emu/cm3) and higher Curie temperature (∼319 K), which results from the crystallinity and strain in the LSMO phase. In addition, the LSMO:ZnO/ZnO/mica film presents a high MR value of ∼39% at 10 K under 1 T. Furthermore, the good mechanical stretchability and property stability of the nanocomposite thin films have been demonstrated with mechanical bending.

Perpendicular Manganite Magnetic Tunnel Junctions Induced by Interfacial Coupling.

The half-metallic manganite oxide La2/3Sr1/3MnO3 (LSMO) has a very high spin polarization of ∼100%, making it ideal for ferromagnetic electrodes to realize tunneling magnetoresistance (TMR). Because of the in-plane magnetic anisotropy of the ferromagnetic LSMO electrode, which leads to the density limit of memory, realizing perpendicular tunneling in manganite-based magnetic tunnel junctions (MTJ) is critical for future applications. Here, we design and fabricate manganite-based MTJs composed of alternately stacked cobaltite and manganite layers that demonstrate strong perpendicular magnetic anisotropy (PMA) induced by interfacial coupling. Moreover, spin-dependent tunneling behaviors with an out-of-plane magnetic field were observed in the perpendicular MTJs. We found that the direct tunneling effect plays a dominant role in the low bias region during the transport behavior of devices, which is associated with thermionic emission of electrons or oxygen vacancies in the high bias region. Our works of realizing perpendicular tunneling in manganite-based MTJs lead to new approaches for designing and developing all-oxide spintronic devices.

Comparison of topotactic and magnetic structures for manganite oxide films

Deliberate manipulation of topotactic transformation via oxygen insertion/extraction offers a feasible way to precisely tune oxygen concentration, B–O coordination occupation and resultant electronic functionalities of perovskite (ABO3)-based oxides. Herein, two methods, a post-annealing CaH2 treatment and an in-situ oxygen-vacancy diffusion using oxygen getter layer, were conducted to achieve topotactic transitions from perovskite to brownmillerite of La0·7Sr0·3MnO3-δ (LSMO, 0 ≤ δ ≤ 0.5) films. The results revealed that delicate control of oxygen composition is the crucial factor for evolutions of crystalline structure and subsequent magnetic properties of LSMO films. In particular, the brownmillerite LSMO film treated by the in-situ oxygen getter layer possesses desirable structural stability over time. In contrast, the topotactic LSMO films using reduction agents CaH2 exhibit compositional and structural inhomogeneities. These findings suggest that adjustable topotactic transformation through anionic oxygen provides a facile strategy for designing multifunctional perovskite-derivative oxide materials.

Emergent perpendicular magnetic anisotropy at the interface of an oxide heterostructure

Controlling the magnetic anisotropy in magnetic oxides is critical for the development of oxide spintronics. Here we report on the finding of an emergent interfacial magnetism, with unique perpendicular magnetic anisotropy (PMA), at the interface of a half-doped manganite ${\mathrm{La}}_{1/2}{\mathrm{Sr}}_{1/2}\mathrm{Mn}{\mathrm{O}}_{3}$ film on $\mathrm{LaAl}{\mathrm{O}}_{3}$ substrate, through combined electron spin resonance measurements and density functional theory calculations. The interfacial magnetism can be explained by the $3{d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital-mediated ferromagnetic exchange interaction between Mn ions near the interface, which is enhanced by the compressive strain from the substrate. Our results provide a useful PMA system for possible spintronic applications, as well as atomistic-level insight to the magnetic anisotropy in strained manganite oxide interfaces.

Ferromagnetism in ultrathin surface-free La0.7Sr0.3MnO3 layers in electrostatically defined heterostructures

Electrostatically defined perovskite oxide heterostructures, in which carriers are confined by the modulation of the A-site ion charge, offer new possibilities of tuning the magnetic properties of manganite oxides. We investigate the preferential orientation of ferromagnetic and antiferromagnetic moments in ultrathin ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ layers embedded in antiferromagnetic $\mathrm{Sr}{\mathrm{MnO}}_{3}$ as they undergo a metal-to-insulator transition with decreasing thickness. Our results evince the role of orbital occupation, metallicity, and competition of different magnetic phases, in absence of spurious effects occurring in thin films as a result of symmetry breaking at ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ interfaces and of incorporation of oxygen vacancies.

Annealing modulated magnetism in double-perovskite PrBaMnFeO5.5+δ ferromagnetic insulator

Double-perovskite oxides are known to exhibit important electronic, magnetic, and electrochemical properties, including metal-insulator transition, colossal magnetoresistance, and excellent mixed conductivity. Here, single-crystalline PrBaMnFeO5.5+δ thin films were epitaxially grown and sensitively tailored to a tunable ferromagnetic state by post-annealing. The drastically tunable ferromagnetism is attributed to the detailed atomic microstructures, localized oxygen vacancy distribution, and exchange interactions between Mn and Fe ions with different valences. The as-grown PrBaMnFeO5.5+δ epitaxial film exhibits saturation magnetization twice that of undoped PrBaMn2O5.5+δ, probably owing to the synergistic reaction of Mn3+–O–Mn4+ double exchange and Mn3+–O–Fe3+ superexchange interactions. These findings suggest that the PrBaMnFeO5.5+δ double-perovskite film can be an effective ferromagnetic insulator with the strategic magnetic properties of complex manganite oxides tuned by chemical strains.

Optimization of Contact Cathode Composition Based on La0.8Sr0.2MnO3±δ for SOFC Stacks

A stack based on planar solid oxide fuel cells (SOFCs) is an assembly of ceramic plates - membrane-electrode assemblies (MEA) and metal current collectors, which play the role of the distribution of gas mixtures over the electrode area, as well as current collection. In order to organize the high-quality current collection it’s necessary to provide a reliable electrical contact between the MEA’s electrodes and contact surfaces of the current collectors. Electrical contact between MEAs’ anode electrode and the collector is achieved by pressing the contact nickel meshes. Metal-based conductive adhesives are also used to reduce the contact resistance at the anode electrode. Despite this in order to ensure contact between the MEA’s cathode electrode and the collector this approach is not applicable due to the rapid oxidation of contact meshes in air atmosphere at high temperatures. In turn, contact pastes based on conductive ceramics do not have such a drawback and make it possible to ensure reliable contact under the conditions of the SOFC cathode chamber.Materials for the contact adhesive for the SOFC cathode chamber must be chemically and thermomechanically compatible with the materials of the SOFC cathode and bipolar plate along with high electrical conductivity. These requirements are met by materials based on lanthanum strontium manganite oxide (LSM) materials, which are widely used as cathode materials for SOFCs. It should be noted that the contact adhesive must also correspond to the limitations of technological processes of SOFC stack manufacturing. SOFC stacks are sealed with glass in a temperature range of 930-950°C, so it’s necessary to use a material that forms a conductive contact at temperatures not higher than 950°C, which is significantly lower than typical sintering temperatures of LSM-based cathode.The synthesis of single-phase highly dispersed powders with the composition of La0.8Sr0.2MnO3±δ (LSM) and (La0.8Sr0.2)0.97MnO3±δ (LSM-d) was carried out by the glycine-nitrate method. After synthesis some of the obtained materials were ball-milled in ethanol using 5 mm ceramic milling bodies at a speed of 600 rpm for 300 and 600 min. A mixture of polyvinyl butyral, toluene, and butanol was used as the basis for the contact paste.Tests of the electrical conductive properties of contact pastes were carried out in air in temperature range of 600-950°C. Samples were kept for 2 hours before cooling at the maximum temperature. Figure shows the results of resistivity measurements: the dashed lines represent the values obtained when the sample was cooled.The maximum values of the resistivity at a temperature of 850°C were obtained for contact adhesive samples based on non-activated stoichiometric (LSM) and A-deficient (LSM-d) powders. Low electrical conductivity can be associated with weak intergranular contact due to the strong agglomeration of the material after synthesis. Grinding for 300 minutes results in a noticeable reduction in the resistivity of the contact adhesive (LSM-300). Change in resistivity after holding at maximum temperature, as well as the change in the slope of the temperature dependence of the resistivity of the adhesive based on LSM-300 indicates the sintering of the contact adhesive powder into a ceramic compact, which is confirmed by SEM results. In turn, holding at a temperature of 950°C of contact adhesive based on LSM-600 (600 min grinding pre-activated) powder does not lead to its sintering.Grinding of the initially single-phase LSM powder results in the appearance of additional reflections in the XRD-spectrum corresponding to the Sr(OH)2 and MnCO3 phases. An increase in the grinding time leads to an increase in the proportion of impurity phases that prevent the contact adhesive from sintering at temperatures <950°C.Thus, the best results were shown by a contact adhesive based on stoichiometric LSM powder, pre-activated by grinding for 300 minutes. Holding at a temperature of 950°C leads to sintering of LSM-300 powder into ceramics, which makes it possible to form a reliable electrical contact under the conditions of the SOFC cathode chamber.We have proposed a method for the manufacture and deposition of a contact cathode composition based on La0.8Sr0.2MnO3±δ. It is shown that the initial powders obtained by the glycine-nitrate method according to the Pechini modification are preliminary prepared. The optimal grinding parameters have been determined. The sintering modes of the contact paste are selected, which are consistent with those for the sealing glass. An experimental SOFC assembly was made using a contact cathode paste. It is shown that the electrochemical characteristics of individual MEAs correspond to the declared ones and the specific power reaches 0.25W/cm2.This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071. Figure 1

Thermal relaxation in a disordered one-dimensional array of interacting magnetic nanoparticles

We consider a system of single-domain magnetic nanoparticles placed along a linear chain and address the effect of the distance between them on the magnetic and thermal relaxation properties of the system. The nanoparticles interact with each other through the dipolar interaction and we introduce disorder into the system by allowing random sizes of the nanoparticles and random directions of their uniaxial anisotropy axes. In particular, the radius of the spherical nanoparticles are drawn from a log-normal distribution. The dynamical behavior of the magnetic moments of the system is studied through numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation, taking into account explicit temperature dependence of the saturation magnetization and uniaxial anisotropy energy density to describe the magnetic properties of perovskite manganite oxide nanoparticles. Hysteresis, zero-field-cooled and field-cooled curves are measured, from which we can find the coercive field and the blocking temperature as a function of the magnitude of the dipolar coupling, controlled by the distance between the particles. We show that both the coercive field and blocking temperature decrease as a function of the separation between the nanoparticles. The magnetic relaxation is measured as a function of both temperature and time, from which we estimate the effective energy barrier distribution of the system. We show that the peak of the energy barrier distribution moves to lower energies as the separation between neighboring particles increases, or equivalently, as the dipolar interaction is reduced.

Solubility Relationship of Metals in Acid Soils of Kumaon Himalaya Region of India

ABSTRACT This study evaluated metal availability under acidic soil conditions and identified the solid phases that govern their solubility using Baker soil test. Free metal ion activity (Mn+) expressed as negative logarithm value (pMn+ = -log10 Mn+) of iron (pFe3+), manganese (pMn2+), copper (pCu2+), zinc (pZn2+), nickel (pNi2+), cadmium (pCd2+), and lead (pPb2+) ranged from 17.5 to 21.3, 5.2 to 8.4, 12.2 to 15.3, 9.3 to 11.9, 11.5 to 14.8, 11.8 to 15.1, and 10.9 to 13.4, respectively. The activities of Fe, Cu, Zn, Ni, Cd, and Pb in the soil solution are likely to be buffered by exchange reactions rather than precipitation-dissolution reactions. However, bixybite and manganite oxides are likely to govern the free Mn2+ activity in the soils. Based on intensity and quantity parameters, the soils were found to have sufficient supply power for plant essential elements (i.e. Fe, Mn, Cu, Zn, and Ni) except in the coarse-textured soils of Kosi. Nevertheless, the toxicity of iron in Someshwar and cadmium in Dhaili soils is expected under the prevailing soil conditions. The generated information on the solubility vis-à-vis availability of metals under acidic soil conditions will contribute to enlarge a field of research which is crucial for land management and deserves more attention, particularly in the fragile mountainous ecosystem.

Hydrogenation driven structural transformation and adjustable electronic properties of epitaxial La0.3Sr0.7MnO3− δ films

Manganites (R1−xAxMnO3, R = rare-earth cation and A = alkali or alkaline earth cation) host an immense number of phases and electronic properties, which can be mainly manipulated through conventional structural control such as metallic cations, oxygen concentration, or misfit strain. However, their practical applications are heavily hindered due to the requirement of rigid synthesis conditions and prolonged treatment time. Herein, a subtle hydrogenation of canonical epitaxial La0.3Sr0.7MnO3 films gives rise to a series of structural transformations ranging from the perovskite to the intermediate state and to the brownmillerite one, accompanied by tunable electronic performances from the antiferromagnetic insulating phase to the weak magnetic insulating one. Moreover, the hydrogenated La0.3Sr0.7MnO3−δ films show an ultra-high magnetic temperature (&amp;gt;400 K). The efficient modulations of the crystalline structure and functionalities of manganite oxides using the facile hydrogenation process enable practical applications of high-temperature magnetic insulators in spintronic devices.