Perovskite Manganites Research Articles

Influence of synergistic effect of Mn valence state and oxygen vacancy concentration on microwave absorbing properties of CaMnO3

The research of microwave absorption material has great significance for solving electromagnetic pollution and military security. Manganite perovskite has huge potential for developing into a fine microwave absorption material due to its adjustable electromagnetic property, while the mechanisms are still being explored. Therefore, we aim to explain the microwave loss mechanism of manganite perovskite with the double exchange interaction of Mn ion. Orthorhombic structure CaMnO3 was effectively synthesized, and the Mn valence state and oxygen vacancy concentration were changed by doping at Ca-site, while the total number of Mn ions remained intact. Ba, Sr, La, Sm, and Ce were the doping ions employed. Analyses revealed that the microwave absorption performance of CMO was linked to the Mn valence state and oxygen vacancy concentration. The Sr-CMO with the optimal microwave attenuation capability had the most Mn3+ ions and its dielectric loss is primarily due to polarization relaxation loss. In the microwave attenuation mechanism of La-CMO, which had the least oxygen vacancy content, conductive loss played a larger role. Through the double exchange interaction of Mn, the synergistic impact altered the microwave absorption performance. Hence, we can manipulate Mn valence state and oxygen vacancy concentration to improve the microwave absorption performance of CaMnO3, and the technique might be applied to other Mn-based absorbents.

Coaxial cable-like dual conductive channel strategy in polypyrrole coated perovskite lanthanum manganite for high-performance asymmetric supercapacitors

Perovskite transition metal oxides are promising materials for supercapacitor electrodes due to their high theoretical capacities. However, these materials still suffer from poor conductivity, low specific capacitance, and moderate cycle stability, restraining their practical applications. In this study, LaMnO3@CC-PPy materials were prepared by two-step electrodeposition based on the inspiring design of coaxial cables. To this end, electrochemically active LaMnO3 was first grown on carbon cloth (CC) with good flexibility and conductivity and then followed by further coating with polypyrrole (PPy) layer. The best PPy load was identified by adjusting the deposition time. The resulting LaMnO3@CC-PPy electrodes showed excellent specific capacitance reaching 862F g−1 at 1 A g−1 with retention rate of 75% at high current density of 10 A g−1, indicative of excellent rate performance. The cycle stability of the electrodes also improved after 3000 cycles at 10 A g−1 with a retention rate reaching 66%. To assemble asymmetric supercapacitor (ASC) devices, NiCo2O4@CC cathodes were prepared by electrodeposition. Ultra-high energy density of about 73 Wh kg−1 and good cycle stability were recorded with the devices. The high performance of the as-obtained materials was attributed to the existence of internal and external double electric channels, as well as the abundant internal space. These features ensured good conductivity, rapid charge transfer, and fast ion diffusion, thereby significantly improving the overall material cycle stability. In sum, these findings look promising for future preparation of high-performance perovskite supercapacitors.

Effect of small cation occupancy and anomalous Griffiths phase disorder in nonstoichiometric magnetic perovskites

The structural, magnetic, magnetocaloric and Griffiths phase (GP) disorder of non-stoichiometric perovskite manganites La0.8−xSr0.2−yMn1+x+yO3 are reported here. Determination of valence states and structural phases evidenced that the smaller cations Mn2+ and Mn3+ will not occupy the A-site of a perovskite under atmospheric synthesis conditions. The same analysis also supports that the vacancy in the A-site of a perovskite induces a similar vacancy in the B-site. The La3+ and Sr2+ cation substitutions in the A-site with vacancy influences the magnetic phase transition temperature (TC) inversely, which is explained in terms of the electronic bandwidth change. An anomalous non-linear change of the GP has been observed in the Sr-substituted compounds. The agglomeration of Mn3+-Mn4+ pairs (denoted as dimerons), into small ferromagnetic clusters, has been identified as the reason for the occurrence of the GP. A threshold limit of the dimeron formation explains the observed non-linear behaviour of the GP formation. The Sr-substituted compounds show a relatively large value of isothermal entropy change (maximum 3.27 J/kgK at μ0H=2T) owing to its sharp magnetic transition, while the broad change of magnetization in the La-substituted compound enhances the relative cooling power (maximum 98 J/kg at μ0H=2T).

Research Progress of Doped Manganite Materials in Magnetic Refrigeration

Magnetic refrigeration technology is a new, green, high-efficiency approach. It has attracted increasing attention from researchers and has a strong competitiveness over traditional refrigeration methods. With the continuous development of social lives, magnetic refrigeration technology must have important application prospects. This article briefly describes the basic principles. The focus is on the introduction and summary of research on perovskite manganite doping in magnetic refrigeration. Finally, the outlook and summary of magnetic refrigeration technology are presented.

Electro−Photo Double Control of Resistive Switching in Electron‐Doped La0.9Hf0.1MnO3 Films

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.

Investigation of reactive perovskite materials for solar fuel production via two-step redox cycles: Thermochemical activity, thermodynamic properties and reduction kinetics

The investigation and optimization of solar fuels production by H2O and CO2 splitting reactions using non-stoichiometric redox materials as oxygen carriers relies on materials-related studies. The thermochemical cycles performance strongly rely on the thermodynamics and kinetics of redox reactions, as well as the chemical composition and morphology of the reactive redox materials commonly based on ceria and perovskites. This study focusses on the evaluation and selection of suitable non-stoichiometric metal oxides for two-step thermochemical cycles with high fuel production yields, rapid reaction rates, and performance stability. The redox activities of different A- and B-site substituted perovskite materials (ABO3) were experimentally investigated (with A = La, Sr, Y, Ca, Ce, Pr, Sm and B = Mn, Co, Fe, Mg, Al, Ga, Cr). The reactive powders were synthesized via modified Pechini methods providing a porous microstructure especially suitable for thermochemical cycles, while their redox activity was evaluated by thermogravimetric analysis. This experimental screening highlighted the difficulty to combine high reduction extent (δ) achievable by the reactive material with complete re-oxidation extent and fast reaction rates. From the redox activity study of manganite perovskites, La0.5Sr0.5Mn0.9Mg0.1O3 (LSMMg) was pointed out as a good compromise between CO2 splitting activity and thermal stability, possibly competing with ceria as a promising material for two-step thermochemical cycles. Both thermodynamic and kinetic studies were also performed to provide a better understanding of the mechanisms involved in thermochemical cycles. Thermodynamic properties derived from experimental δ(T,pO2) diagrams were used to predict the upper bounds for both reduction extent and fuel production performance at equilibrium. Regarding kinetics, the activation energy during LSMMg reduction was shown to increase with the increase of the non-stoichiometry extent.

Redox cycle of calcium manganite for high temperature solar thermochemical storage systems

Thermochemical energy storage via metal oxide redox cycling is a potential cost-effective approach to store solar energy both chemically and thermally at high temperatures, enabling efficient solar thermal power production round-the-clock and on-demand. Perovskite manganites are a low-cost redox material that undergoes reversible reaction without side reactions up to 1000 °C and offers high storage capacities, which makes them promising energy storage materials in next-generation solar thermal power plants. In this study, the thermal properties of a typical perovskite manganite, CaMnO3, has been studied. CaMnO3 shows 893.2 kJ/kg energy storage capacity from 200 °C to 1000 °C, and 0.133 non-stoichiometry in N2. The material exhibits excellent stability with 150 redox cycles between 500 °C and 1000 °C. The thermodynamic efficiencies of two solar-driven combined cycle power systems with CaMnO3 based thermochemical energy storage system are also investigated. The steady-state mass and energy conservation equations are solved for all system components to calculate the thermodynamic properties and mass flow rates at all state points in the system. Preliminary results for a system with 120 MW nominal solar power input at a solar concentration ratio of 1000 are presented, designed for constant round-the-clock operation with 9 h of on-sun and 15 h of off-sun operation. The CaMnO3 particles store and release energy via the sensible heat and reaction heat, yield a net power block efficiency of approximately 60% and an overall energy conversion efficiency of up to 48.7%. Required storage tank sizes for the solids are estimated to be up to 2–3 smaller than those of state-of-the-art molten salt systems.

Elastic and magnetoelastic properties of TbMnO3 single crystal by nanosecond time resolved acoustics and first-principles calculations

Time resolved pump and probe acoustics and first-principles calculations were employed to assess elastic properties of the TbMnO3 perovskite manganite having orthorhombic symmetry. Measuring sound velocities of bulk longitudinal and shear acoustic waves propagating along at least two different directions in the high symmetry planes (100), (010) and (001), provided a powerful mean to selectively determine the six diagonal elastic constants C 11 = 227 GPa, C 22 = 349 GPa, C 33 = 274 GPa, C 44 = 71 GPa, C 55 = 57 GPa, C 66 = 62 GPa. Among the three remaining off-diagonal ones, C 23 = 103 GPa was determined with a bissectrice direction. Density functional theory calculations with colinear spin-polarized provided complementary insights on their optical, elastic and magnetoelastic properties.

Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space‐Charge Phenomenon

AbstractIn displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO3+δ is an atypical acceptor‐doped perovskite‐type oxide. In this study, 18O/16O diffusion experiments on epitaxial thin films of La0.8Sr0.2MnO3+δ and molecular dynamics (MD) simulations are combined to elucidate the origin of this phenomenon for dislocations: Does diffusion occur along dislocation cores or along space‐charge tubes? Transmission electron microscopy studies of the films revealed dislocations extending from the surface. 18O penetration profiles measured by secondary ion mass spectrometry indicated (slow) bulk diffusion and faster diffusion along dislocations. Oxygen tracer diffusivities obtained for temperatures 873 ≤ T [K] ≤ 973 were over two orders of magnitude higher for dislocations than for the bulk. The activation enthalpy of oxygen diffusion along dislocations, of (2.95 ± 0.21) eV, is surprisingly high relative to that for bulk diffusion, (2.67 ± 0.13) eV. This result militates against fast diffusion along dislocation cores. MD simulations confirmed no accelerated migration of oxide ions along dislocation cores. Faster diffusion of oxygen along dislocations in La0.8Sr0.2MnO3+δ is thus concluded to occur within space‐charge tubes in which oxygen vacancies are strongly accumulated. Reasons for and the consequences of space‐charge zones at extended defects in manganite perovskites are discussed.

Improved room-temperature TCR of La0.7Ag0.125K0.175MnO3 films by optimizing sintering temperatures

Cation-doped perovskite manganite has unique electrical transport properties; therefore, it has attracted attention due to its promising applications in the field of uncooled infrared bolometers. For the bolometer applications, high temperature coefficient of resistivity (TCR) at room-temperature is essential for the perovskite materials. To investigate the effect of sintering temperature (Ts) on TCR and obtain high TCR values of manganite films at room temperature, La0.7Ag0.125K0.175MnO3 (LAKMO) films were prepared on the (001) SrTiO3 substrate at various Ts via sol–gel spin coating method. Using analysis of structure, morphology, ionic valence, and electrical transport properties, LAKMO films with better crystalline quality and larger TCR values were obtained at higher Ts. The TCR value of LAKMO films reached a maximum value (9.46 % K−1) and the TCR peak temperature (Tk) reached room-temperature (298.75 K) at Ts of 1000 °C, indicating that the material has great potential for the uncooled infrared bolometer applications.

Correlating X-ray absorption spectra and ultraviolet photoelectron spectra to understand magnetic and transport properties of charge-ordered perovskite manganites

X-ray absorption spectra and ultraviolet photoelectron spectra have been used to compare the electronic structures of (La0.6Pr0.4)0.65Ca0.35MnO3 and (La0.4Pr0.6)0.65Ca0.35MnO3 systems to understand their magnetic and transport properties. Structural analysis showed that increased Pr-substitution triggers expansion in apical Mn-O bond lengths, which eventually causes narrowing of the eg band width. (La0.6Pr0.4)0.65Ca0.35MnO3 exhibits ferromagnetic ordering below 215 K and shows semiconductor to metal transition around 212 K, while (La0.4Pr0.6)0.65Ca0.35MnO3 exhibit complex magnetic behaviour and also show local semiconductor to metal transition around 95 K before re-entering into semiconducting region again below 80 K. A slight change in the slope of resistivity around 220 K and four orders increase in resistivity indicates presence of charge-ordering in (La0.4Pr0.6)0.65Ca0.35MnO3. Moreover, (La0.4Pr0.6)0.65Ca0.35MnO3 exhibits ~ 100% magneto-resistance. X-ray absorption studies of Mn-L2,3 edge and O-K edge reveal the onset of Mn3+-Mn4+ charge-ordering in (La0.4Pr0.6)0.65Ca0.35MnO3 at room temperature. O-K edge spectra exhibits an increased spectral intensity of O2p-Mn3d(eg) states near Fermi-level for (La0.4Pr0.6)0.65Ca0.35MnO3, which reflects the number of unoccupied eg states. Valence band ultraviolet photoemission spectroscopy study revealed that Mn3d(eg) states of (La0.6Pr0.4)0.65Ca0.35MnO3 extends into conduction band by crossing-over the Fermi-level. On the other hand, (La0.4Pr0.6)0.65Ca0.35MnO3 exhibits no electronic state at Fermi-level explaining stronger semiconducting nature of x = 0.6 system than x = 0.4 near room temperature.

Tuning the Phase Separation, Charge Ordering, and Electronic Transport in Electron‐Doped Manganite Films by Piezo‐Strain and Magnetic Field

AbstractThe macroscopic physical properties and functionalities of strongly correlated complex oxides usually originate from and depend sensitively on microscopic interactions, which can be controlled by an external stimulus. Here, in electron‐doped La0.85Hf0.15MnO3/Pb(Mg1/3Nb2/3)O3‐PbTiO3 multiferroic heterostructure, the role of phase separation in manipulating charge ordering and electronic transport by piezo‐strain and magnetic field is determined. The electric‐field‐induced lateral compressive piezo‐strain suppresses the charge‐ordering transition temperature and decreases the film resistance with a giant gauge factor of 27 368, due to the enhancement of the double‐exchange interaction between the Mn3+–Mn2+ ions and the suppression of the electron‐phonon coupling stemming from the Jahn‐Teller deformation. Moreover, the magnetic field can weaken the piezo‐resistance effect by 342 times. This result, together with elastically controlled magnetoresistance effect, demonstrates intimate correlation between the piezo‐strain‐induced and magnetic‐field‐induced effects by adjusting phase separation tendency. The findings indicate the importance of phase separation in multi‐field quantum control of electron‐doped perovskite manganites.

Asymmetric interfaces sandwiched between infinite-layer oxides and perovskite oxides

Asymmetric heterointerfaces that bridge two nonisostructural oxides provide valuable opportunities for novel emergent phenomena that may be unavailable for symmetric interfaces. Here we present a theoretical investigation on three different asymmetric interfaces consisting of the infinite-layer nickelate $\mathrm{LaNi}{\mathrm{O}}_{2}$ and the perovskite manganite $\mathrm{LaMn}{\mathrm{O}}_{3}$ (type A, B and C). An alternative crystal geometry, pyramid, is introduced when the planar-type $\mathrm{LaNi}{\mathrm{O}}_{2}$ and the $\mathrm{LaMn}{\mathrm{O}}_{3}$ are jointed at the interface, resulting in strong charge and orbital reconstruction. For type A interface, the magnetic moment per Mn ion has increased by 10% due to the replacement of $\mathrm{Mn}{\mathrm{O}}_{6}$ by $\mathrm{Mn}{\mathrm{O}}_{5}$. For type B interface, in contrast, the magnetic moment grew by 26% for the interfacial Ni ions due to the strong charge transfer between center nickel and apical oxygen. For type C interface, only slightly enhanced $\mathrm{Mn}{\mathrm{O}}_{6}$ distortions are observed and thus the change of charge and orbital occupancy are negligible. Our results demonstrated that an interface-selective orbital occupancy, where the Mn ${e}_{\mathrm{g}}$ orbital preferential occupation alternated from the out-of-plane ${\mathrm{d}}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ state at type A interface to nearly degenerate at type C interface and then to in-plane ${\mathrm{d}}_{{x}^{2}\ensuremath{-}{y}^{2}}$ state at type B interface. The values of relative change of Mn ${e}_{\mathrm{g}}$ orbital occupancy are 15%, 2%, and \ensuremath{-}21%, respectively. The values of relative change at type A and B interface are larger than that achieved by strain $(\ensuremath{\sim}5%)$ or symmetric interface design (10%). Therefore, interface reconstructions lead to unusual electronic properties, opening space for the advancement of oxide electronics.

Negative magnetization induced by particle-size reduction in Gd1−xCaxMnO3 nanoparticle systems

We report a pervasive phenomenon of gradual emergence of negative magnetization in typical $R_{1-x}D_x$MnO$_3$ orthorhombic perovskite manganites in nano form (with $R^{3+}$ being a trivalent high-magnetic-moment ion from the heavier rare-earth elements Gd, Tb, Dy and $D^{2+}$ refers to divalent alkaline elements Sr, Ca, etc.), while the bulk form manifests no negative magnetization. Extensive magnetization studies have been carried out in Gd$_{1-x}$Ca$_x$MnO$_3$ manganites around half doping. We demonstrate experimentally that particle size reduction in nano-form manganites enhances the propensity of the system to exhibit negative magnetization and provide a theoretical explanation for the phenomenon. To test the universality of our findings, we have extended the measurement to Dy$_{0.6}$Ca$_{0.4}$MnO$_3$ and obtained similar results.

Robust temperature coefficient of resistance of polycrystalline La0.6Ca0.4MnO3 under magnetic fields at room temperature

In the presence of magnetic field, reducing the loss in temperature coefficient of resistance (TCR) and increasing metal−insulator transition point (TMI) to room temperature are the most important concerns for the application of perovskite manganites in high−precision thermistors. Based on emerging evidence, relevant factor to address these problems lies in the interaction between Jahn−Teller (JT) distortion and magnetic field, which results in spin−orbital coupling (SOC) effect and significantly influences TCR and TMI. In this work, we studied the magnetic field induced SOC effect in polycrystalline La1−xCaxMnO3 (x = 0.225–0.45) materials synthesized via sol−gel technique. Compounds undergo the JT distortions with increasing Ca dopant content, and the most pronounced distortion of 0.0144 at x = 0.40 is correlated with a basal−plane distortion mode. All samples exhibit TMI values between 262 K and 288 K, indicating the enhancement of doping−induced double−exchange interaction. In the magnetic field of 1 T, SOC effect sufficiently suppresses the deterioration of TCR caused by deficient magnetization in La0.6Ca0.4MnO3 to a value of 2.9%·K−1 at room temperature (287 K).

Examination of the usability of La0.67Ba0.33MnO3 perovskite manganite compound with magnetocaloric effect in magnetic cooling technology

Perovskit manganit yapılı bileşikler yüksek manyetokalorik etki (MKE) ve devesa manyetodirenç (DMD) etkileri göstermeleri nedeniyle son yıllarda oldukça yaygın olarak çalışılan malzemelerdir. ABO3 formundaki perovskit manganit bileşikleri, ideal durumda iken antiferromanyetik ve yalıtkan özellik sergilerken, A-bölgesine yapılan +1 ve/veya +2 değerlikli element katkısı ile ferromanyetik ve iletken özellik göstermektedir. Perovskit manganit bileşikler elektriksel ve manyetik özelliklerini katkılamalar ile değiştirilebilir ve yığın olarak kolayca üretilerek şekillendirilebilir olmasının yanında, gösterdikleri yüksek MKE nedeniyle yeni tip soğutucu elemanı olarak manyetik soğutma (MS) sistemlerinde etkin olarak kullanılacak yeni tip malzeme olma özelliği taşımaktadır. Bu çalışmada, alaşımlar yerine daha ucuza mal edilen ve şekillendirilmesi kolay olan perovskit manganit bileşiği ele alınmıştır. İdeal durumdaki LaMnO3 perovskit manganit bileşiğinde La eksiltilerek yerine %33 (1/3) oranında Ba katkılanmıştır. Ba katkılanan La0.67Ba0.33MnO3 bileşiği sol-jel metodu kullanılarak üretilmiş ve yığın olarak elde edilmiştir. Daha sonra örnek 1000oC’de 24 saat ısıl işleme tabi tutulmuş, yapısal ve manyetik özellikleri incelenmiştir. Perovskit manganit bileşiğin X-ışınları kırınım deseni üzerinden yapılan arıtım sonucunda bileşiğin kübik yapıda olduğu tespit edilmiş ve Pm3m uzay grubuna ait olduğu bulunmuştur. SEM analizlerinden tane boyutunun 100-200 nm aralığında değiştiği gözlenmiştir. Sıcaklığa bağlı yapılan mıknatıslanma ölçümlerinden La0.67Ba0.33MnO3 perovskit manganit bileşiğinin Curie geçiş sıcaklık (TC) değeri 341 K, 1 T manyetik alan altında hesaplanan manyetik entropi (-ΔSM) değeri 0.87 Jkg/K ve manyetik soğutucu malzeme olarak kullanılabilirliğini gösteren göreli soğutma gücü (RCP) değeri 38 J/kg olarak hesaplamıştır.

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.

Electronic structure and energy gaps evaluation of perovskite manganite single crystals using XES and XAS spectroscopy

In this work, the X-ray absorption spectroscopy (XAS), and emission spectra spectroscopy (XES) carried out in synchrotron radiation, were employed to evaluate the electronic structure, and bandgap energy of perovskite manganese: LaSr2Mn2O7, La1.2(Ba, Ca)1.8Mn2O7 and La0.95Ba0.05MnO3 single crystals. Atomic multiple calculations also have been utilized to assess the Jahn-Teller distortion and extracting quantitative details on the ligand metal charge transfer (LMCT). We find that Mn ions possess mixed oxidation states Mn3+/Mn4+ as dominated ground configurations with a small fraction of Mn2+. The trivalent Mn3+ (Mn2O3) exist with high spin (HS) 2p3d4 (e g3 t2 g1). The band edge positions and bandgap energy are remarkably influenced by Alkaline (Ba/Ca) dopant ions as well as by temperature, where, the low temperature causes the bandgap to be significantly narrowing and that has been stated and discussed.

Machine Learning Model for High-Throughput Screening of Perovskite Manganites with the Highest Néel Temperature

Neel temperature (TN), the antiferromagnetic to paramagnetic phase transition temperature, is also one of the important magnetic properties of antiferromagnets. Antiferromagnets could be used to write and read information below TN in electronic memory devices. Perovskite manganites are an important antiferromagnetic material with superior magnetic properties. However, it is challengeable to seek novel perovskite manganites with TN higher than room temperature by trial-and-error method. In this work, the maximum correlation minimum redundancy (mRMR) integrated machine learning approaches were used to screen the optimal subset of features, which included chemical compositions and atomic parameters of perovskite manganites. The machine learning model called support vector regression (SVR) was constructed to predict the TN of perovskite manganites. The correlation coefficient (R) between experimental TN and predicted TN reached as high as 0.87 for the training set in leave-one-out cross-validation (LOOCV) and 0.86 for the independent testing set, respectively. The high-throughput screening of new perovskites with higher TN temperature was then carried out by using our online computation platform for materials data mining (OCPMDM). The TN of designed perovskite manganites (Sr0.7Pm0.3MnO3) was predicted to be 307.5K, increasing by 6% compared to the maximum TN of Sr0.9Ce0.1MnO3 (290K) reported. Our machine learning model can be accessible for public on web server: http://materials-data-mining.com/lkl/lkl_model .

Structural, magnetic and Mössbauer studies of Nd 0.6Sr0.4FexMn1-xO3 perovskites

The effect of iron doping on the structural and magnetic properties of the manganite perovskites Nd0.6Sr0.4FexMn1-xO3 (0.1 ≤ x ≤ 1.0) was studied. Auto-combustion sol-gel method was used to prepare the compounds. X-ray diffraction refinement indicated that all the compounds crystallized in orthorhombic single-phase with Pnma space group. Scanning electron microscopy micrographs revealed a group of packed grains of about 0.2–1.0 μm whereas the average particle size was found to be in the range of about 40–80 nm via transmission electron microscopy. The zero-field cooled and field cooled magnetization curves, under an applied magnetic field of 0.02 T, revealed that the samples with 0.1 ≤ x ≤ 0.4 exhibit a paramagnetic to ferromagnetic transition with decreasing temperature while the samples with (0.5 ≤ x ≤ 1.0) do not demonstrate such phase transition. At room temperature the dependence of magnetization on the x iron concentration, as revealed by the corresponding M − H curves, can be interpreted as the cumulative result of changes in superparamagnetic, paramagnetic and antiferromagnetic contributions. 57Fe transmission Mӧssbauer spectra were recorded at room-temperature (295 K) and liquid nitrogen temperature (78 K) for all the samples. Iron ions were found to be present in these compounds exclusively in a paramagnetic high-spin Fe3+ state for 0.1 ≤ x ≤ 0.5 at 295 K and for 0.1 ≤ x ≤ 0.3 at 78 K. At higher iron concentrations an antiferromagnetic state of iron clusters is formed due to the Fe3+ – Fe3+ superexchange interaction. Room temperature 57Fe quadrupole splitting was found to increase near linearly with the x iron concentration up to x = 0.6. For x ≥ 0.6 the formation of paramagnetic Fe4+ is observed at 295 K, which at lower temperatures undergoes charge disproportionation leading to the appearance of Fe5+ species as observed at 78 K. Perturbations of the magnetic state of iron ions was found to lead to substantial broadening of the Mössbauer absorption peaks of magnetic components, which is interpreted as the effect of nearest neighbor Fe5+ and Mn ions at 78 K, and as that of electron-hopping related Fe3+ - Fe4+ valence fluctuations at 295 K.