Behavior Of La0 Research Articles

Tunable magnetic switching behavior in La0.7Sr0.3MnO3/PbTiO3 multilayers

Tuning magnetic switching behavior and related magnetic configuration of transition metal oxides (TMOs) is critical for realizing multifunctional materials and devices. In this study, we manipulated the magnetic switching behavior through interface engineering by introducing ferroelectric PbTiO3 (PTO) to form La0.7Sr0.3MnO3 (LSMO)/PTO multilayers. Both the normal hysteresis loop (NHL) and the inverted hysteresis loop (IHL) could be tuned by changing the PTO thickness. All multilayers displayed a transition from NHL to IHL with increasing temperature, and the transition temperature increased with the insertion of the PTO layer or increasing thickness of the PTO. In addition, it was found that the increase in the Curie temperature (Tc) and saturation magnetization (Ms), as well as the decrease in the coercive field (Hc) and exchange bias field (Heb) with a reduction in the thickness of the PTO, is possibly related to the interface phase. This study illustrates the influence of the ferroelectric PTO thickness on the magnetic switching behavior and related magnetic configuration in LSMO, which is possibly driven by the unscreened depolarization charge and oxygen octahedral tilting. This finding may benefit the application of TMOs in multifunctional memory devices.

Influence of high-pressure heat treatment on magnetocaloric effects and phase transition critical behavior in La0.75Sr0.25Mn0.9Co0.1O3

Influence of high-pressure heat treatment on magnetocaloric effects and phase transition critical behavior in La0.75Sr0.25Mn0.9Co0.1O3

Influence of high-pressure heat treatment on magnetic property and phase transition critical behavior in La0.75Sr0.25Mn1 − xCoxO3 (x = 0, 0.1, 0.2)

In this study, La0.75Sr0.25Mn1−xCoxO3 (x = 0, 0.1, 0.2) samples were synthesized using a high-pressure heat treatment method, and their magnetic properties and critical phase transition behaviors were systematically investigated. The prepared samples exhibited excellent single-phase characteristics with space group R 3¯ c. As the Co content increased, TC decreased from 325 to 211 K. In a 7 T magnetic field, the RCP values of the samples increased from 364.52 to 384.66 J·kg−1, significantly enhancing the cooling efficiency of the samples. The three samples exhibited a second-order phase transition, indicating a relatively small hysteresis in the system. The critical exponents were obtained by MAPs and K-F method. These results indicate that with an increase in Co doping, the β values also increase, suggesting that Co doping facilitates the establishment of long-range ferromagnetic order in the three samples.

Surface Gibbs free energy analyses of Sr segregation in lanthanum strontium iron oxide

Sr surface segregation in mixed-cation oxides often causes degradation of chemical or electrochemical performance. In this work, the thermodynamic driving force for Sr segregation is investigated to explain the Sr segregation behavior in La0.5Sr0.5FeO3 (LSF). Specifically, Density Functional Theory is used to calculate the surface Gibbs free energy of various surface terminations of cubic (100) LSF as a function of chemical potential and temperature. SrO-terminated surfaces are predicted to be dominant, promoting Sr segregation at high temperatures and low oxygen partial pressure.

Effect of angstrom-level oxide overcoat on Sr segregation behavior of LSM electrodes

Long-term durability of perovskite (ABO3)-based cathodes in solid oxide fuel cells has been largely limited by surface segregation of A-site dopant and thermal agglomeration. Since a deposition of an atomically thin oxide has proven to be highly effective in suppressing electrode agglomeration, a successful suppression of dopant segregation with the same approach will enhance the durability of cathodes significantly by killing two birds with one stone. In this report, we demonstrate that an atomic-scale overcoat with a nominal thickness of 2–3 Å is indeed an effective approach of tuning Sr segregation behavior in La0.8Sr0.2MnO3 (LSM) if a proper choice of the overcoat material is made. Coating of a binary oxide with multi-valent cations (CeO2 and TiO2) desegregates Sr species into the lattice of LSM while an overcoat with single valent cations (ZrO2 and Y2O3) exhibits little effect on Sr segregation. A mechanistic interpretation of the behavior is also presented based upon a series of X-ray photoelectron spectroscopy and electrochemical analyses.

Magnetocaloric effect and critical behavior in La0.8K0.2MnO3 nanoparticle

We report on the magnetocaloric effect and critical phenomenon on La0.8K0.2MnO3 nanoparticle through a systematic magnetic and electrical measurement. The magnetic entropy change (ΔSM) presents close values obtained from resistivity and magnetic measurements, however, with a discrepancy in the magnetic entropy maximum values. This discrepancy is due to the presence of an extrinsic effect associated with the nanometric grain size affecting the electrical behavior. Interestingly, our results show a good agreement with the calculation of the critical exponents and the temperature coefficient of resistance shows positive and negative values. The obtained critical exponents are close to that of the mean-field theory (with β = 0.5, γ = 1, and δ = 3). This indicates a long-range interaction between spins a consequence of the presence the presence of dipole- dipole interaction in this system.

Kinetic insight into perovskite La0.8Sr0.2VO3 nanofibers as an efficient electrocatalytic cathode for high‐rate LiO2 batteries

AbstractEfficient electrocatalysis at the cathode is essential for overcoming the limitations of LiO2 batteries such as poor stability and low rate capability. Herein, we systematically studied the kinetic behavior of a LiO2 battery comprising perovskite La0.8Sr0.2VO3 nanofibers formed by partial Sr‐cation doping and V cations with multiple oxidation states. Compared with undoped LaVO3 and La0.8Sr0.2VO4 nanofibers, perovskite La0.8Sr0.2VO3 nanofibers exhibited an improved capacity of 2000 mA g−1, and a 20‐times‐longer cycle life in LiO2 batteries. X‐ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and photoluminescence analyses revealed that the performance variations mainly originated from crystal defects, which modulate oxygen reduction/evolution kinetics. Through in situ Raman analysis, we showed that these structural defects are closely related to the oxygen reduction/evolution behavior of La0.8Sr0.2VO3 nanofibers and result in fewer parasitic reactions. This study offers insights into the potential rate capability of LiO2 batteries and related devices.image

Effects of organic material on magnetoresistance in electron-doped double perovskite

The Curie temperature of electron-doped Sr2FeMoO6 can be optimized significantly due to the band-filling effect, but accompanying an almost absent low-field magnetoresistance (LFMR), which is unfavorable to applications in the magnetoresistive devices operated at room temperature. Our previous works confirmed that, a remarkable enhanced LFMR was observed in Sr2FeMoO6 by modifying the grain boundary with insulating organic small molecules (glycerin, CH2OHCHOHCH2OH). However, in this work, modifying the grain boundary strength of the La0.5Sr1.5FeMoO6 with the insulating organic macromolecules (oleic acid, CH3(CH2)7CH=CH(CH2)7COOH) or small molecules (glycerin), both of them have negligible functions on the magnetoresistance (MR) behavior in La0.5Sr1.5FeMoO6. Contrary to the glycerin-modified Sr2FeMoO6, Sr2FeMoO6/oleic acid composites do not exhibit an obviously increased MR property. Based on the above experimental results and the related works, it is proposed that, maintaining high spin polarization of the carriers at the Fermi level and improving the tunneling process across the grain boundary using the suitable organic materials are decisive factors for optimizing the MR behavior in the similar electron-doped double perovskites.

Influence of Non-magnetic Ti4+ Doped on Critical Behavior of La0.55Pr0.1Sr0.35Mn1 − xTixO3 (x = 0.00, 0.05) Manganites

Influence of Non-magnetic Ti4+ Doped on Critical Behavior of La0.55Pr0.1Sr0.35Mn1 − xTixO3 (x = 0.00, 0.05) Manganites

Percolation conductivity model in A site-deficient La0.8−xoxNa0.2−xoxMnO3 manganites and universal model of magnetic field-dependent resistivity and magnetoresistance behavior

The electrical and magnetoresistance behaviors of La0.8−xoxNa0.2−xoxMnO3 [with x = 0 (N0) and 0.1 (N0.1)] polycristalline samples were investigated. Resistance measurements versus temperature under different magnetic applied fields were performed to investigate the electronic transport as well as the magnetoresistance properties. The metal/insulator transition temperature decreases from 280 K for x = 0 to 275 K for x = 0.1. The electrical conduction in these compounds has been well described in the context of the percolation model based on the phase separation of ferromagnetic metallic regions with paramagnetic insulating ones. The temperature-dependent resistance shows the existence of a minimum at low temperature. This behavior is due to the existence of a competition between inelastic and elastic interactions expressed by Kondo-like spin-dependent scattering. An empirical model was used to describe the variation of the magetoresistance and normalized resistance as a function of the magnetic applied field. The model was successfully widely tested on several magnetic specimens and the evolution of the fitting parameters was discussed in detail.

Effect of Polaron formation in conduction and dielectric behavior in La0.7Sr0.25K0.05MnO3 oxide

The purpose of this paper is to analyze the dielectric properties of La0.7Sr0.25K0.05MnO3 (LSKM) using impedance spectroscopy over the frequency range of 100 Hz to 1 MHz at different temperatures from 260 to 380 K. In fact, the dielectric analyses of the sample showed two relaxation processes at different relaxation times related to the effect of microstructural inhomogeneities and the contribution of grain and gain boundaries. However, Ac conductivity behavior reveals a metal–semiconductor phase transition at a specific temperature TM-S = 260 K and showed an important impact of the electron–lattice interaction in polaron formation. Also, the conductivity curve is analyzed by Johnscher’s universal power law and the variation of the exponent ‘n’ with temperature suggests the domination of small polaron hopping (SPH) model governed by an activation energy Ea = 0.12 eV. Further investigations using modulus formalism proved the presence of electrical relaxation, which is in good agreement with impedance results. The dielectric poly-dispersive behavior is related to the conduction process and the large value of the dielectric constant $$\varepsilon^{\prime\prime}(\omega )$$ in the order of 106 is correlated to the Maxwell–Wagner relaxation.

Modeling of Magnetic and Magnetocaloric Properties by the Molecular Mean Field Theory in La0.6Sr0.4Mn0.9V0.1O3 Oxide

Based on the mean-field theory, the magnetic and magnetocaloric behavior of La0.6Sr0.4Mn0.9V0.1O3 manganese oxide has been analyzed. The Bean-Rodbell equation of state presents a second-order magnetic phase transition with a η factor of η = 0.71. Using the experimental data of magnetization M (H, T), the molecular mean-field parameter is found to be λ1 = 2.19 T g emu−1. The Brillouin function makes it possible to determine the total angular moment J, the saturation magnetization MS, and the Lande factor g for La0.6Sr0.4Mn0.9V0.1O3 sample. We simulated the magnetization as a function of the magnetic field and the temperature by applying the mean-field theory, as well as the variation of the magnetic entropy change ΔSM(T). As observed, the simulated results close with experimental data. The magnetic entropy changes for the samples were also estimated by using the mean-field scaling theory, and the results show a difference between the theoretical and experimental values.

Correlation of exchange-bias effect with negative magnetization in perovskite compound, La0.5Pr0.5CrO3

Detailed investigations of the negative magnetization (NM) phenomenon and associated exchange bias (EB) effect in a single phase perovskite compound, La0.5Pr0.5CrO3, have been carried out. DC magnetization measurement under 200 Oe reveals a magnetic ordering (TN) at 264 K and a magnetization compensation at temperature, TCOMP ∼ 160 K. The compound exhibits NM as well as EB below TCOMP. The temperature and cooling field dependencies of EB have been investigated to reveal the dominant antiferromagnetic (AFM) and ferromagnetic (FM) interactions in La0.5Pr0.5CrO3. Both positive horizontal (HEB) and negative vertical (MEB) shifts (with respect to the origin) of field-cooled hysteresis curves are observed. Interestingly, both magnetization and EB (HEB and MEB) become zero at TCOMP. In addition, the EB (HEB and MEB) effect is maximum for a cooling field of 5 kOe, which is also the maximum field for observing NM behavior in La0.5Pr0.5CrO3, indicating a correlation between EB and NM. Rietveld refined neutron diffraction patterns at various temperatures infer a Gy type AFM ordering of Cr3+ moments below TN. Both NM and positive EB phenomena have been explained by considering the AFM exchange interaction between an induced moment of Pr3+ and a FM component of canted Cr3+ moment. The understanding is significant as it may open up the possibility for making thermomagnetic switches, magnetic memory, and other spintronic devices.

Temperature dependence of transport mechanisms in organic multiferroic tunnel junctions

Organic multiferroic tunnel junctions (OMFTJs) with multi-resistance states have been proposed and have drawn intensive interests due to their potential applications, for example in memristor and spintronics based synapse devices. The ferroelectric control of spin polarization at a ferromagnet/ferroelectric organic (FE-Org) interface by electrically switching the ferroelectric polarization of the FE-Org has been recently realized. However, there is still a lack of understanding of the transport properties in OMFTJs, especially the interplay between the ferroelectric domain structure in the organic barrier and the spin polarized electron tunneling through the barrier. Here, we report on a systematic study of the temperature dependent transport behavior in La0.6Sr0.4MnO3/PVDF/Co OMFTJs. It is found that thermal fluctuation of the ferroelectric domains play an important role on the transport properties. When T > 120 K, the opposite temperature dependence of resistance for up and down ferroelectric polarization states results in a rapid diminishing of the tunneling electroresistance. These results contribute to the understanding of the transport properties for designing high performance OMFTJs for memristor and spintronics applications.

3D-Ising like ferromagnetism in skyrmionic-bubbles host infinite-layer La0.825Sr0.175MnO3 manganite perovskite

The critical behavior of infinite-layer La0.825Sr0.175MnO3 of Ruddlesden–Popper series manganite has been studied around the transition temperature (). To reveal the universality class that explains the critical behavior in La0.825Sr0.175MnO3 several methods, such as modified Arrott plots, Kouvel–Fisher, entropy and critical isotherm analysis have been employed. The critical exponent for infinite-layer is obtained independently from critical magnetization isotherm and found to satisfy the Widom scaling relation . The universality class of the critical phenomenon in infinite-layer La0.825Sr0.175MnO3 manganite can be explained with the help of renormalization group theory approach for three dimensional (3D) systems. We have shown that a short-range 3D-Ising type interaction is responsible for ferromagnetic and second-order phase transition to paramagnetic phase.

Oxygen diffusion and electrochemical performance of La0.6−xSr0.4BaxCo1−yFeyO3−δ

La0.6−xSr0.4BaxCo1−yFeyO3−δ (x = 0, 0.2, y = 0.1, 0.2, 0.3, 0.4) were prepared by the glycine–nitrate process. The electrochemical property and oxygen diffusion behavior of La0.6−xSr0.4BaxCo1−yFeyO3−δ were investigated. The electrochemical impedance spectroscopy analysis suggests that doping with an appropriate amount of iron and barium improves the catalytic performance. La0.4Sr0.4Ba0.2Co0.9Fe0.1O3−δ calcined at 950 °C exhibits the minimum polarization resistance of 0.0349 Ω cm2 at 750 °C. The doping of Fe improves the sintering performance. The crystalline size of La0.6−xSr0.4BaxCo1−yFeyO3−δ becomes smaller with the doping amount of Ba, which increase the number of active sites. The doping of Ba decreases the oxygen vacancy formation energy and increases the oxygen vacancy concentration, which accelerates the oxygen diffusion. Further, the single cell performance for La0.4Sr0.4Ba0.2Co0.9Fe0.1O3−δ as cathode shows the maximum power density of 539.49 W cm−2 at 750 °C.

Confined polaronic transport in (LaFeO3)n/(SrFeO3)1 superlattices

Functional oxide superlattices offer new and exciting possibilities for the exploration of emergent properties at the nanoscale. While the behavior of La1−xSrxFeO3 films has been extensively investigated at low temperatures, few studies have been carried out at high temperatures, particularly for LaFeO3/SrFeO3 superlattice systems. Here, we investigate the transport behavior and optical properties of (LaFeO3)n/(SrFeO3)1 superlattices at 373 K and above. Using optical spectroscopy, we observe a low energy excitation at ∼1 eV, attributable to charge transfer between the O 2p and Fe 3d states of the δ-doped single SrFeO3 layer. From in-plane conductivity measurements on the superlattices, we determine activation energies that are much lower than those of alloyed samples and vary with the total number of SrFeO3 layers. This suggests that polaronic transport is confined near the SrFeO3 regions, permitting mobilities significantly enhanced over those in alloyed thin films.

Room temperature magnetocaloric effect and critical behavior in La0.67Ca0.23Sr0.1Mn0.98Ni0.02O3 oxide

The structural, magnetic and magnetocaloric properties of $${\text{La}}_{0.67} {\text{Ca}}_{0.23} {\text{Sr}}_{0.1} {\text{Mn}}_{0.98} {\text{Ni}}_{0.02} {\text{O}}_{3}$$ nano-crystalline manganite are investigated systematically. The compound is elaborated based on Pechini sol–gel method and then annealed at 1000 °C for 24 h. X-ray powder diffraction shows that, the sample crystallizes in a rhombohedral structure with $$R\overline{3} C$$ space group. A magnetization versus temperature study shows that the compound exhibits a second-order magnetic transition from a ferromagnetic to a paramagnetic state at a Curie temperature $$T_{C}$$ = 296 K. To evaluate the magnetic entropy change $$\Delta S_{M}$$ , we measure the magnetization as a function of temperature and magnetic field. At ambient temperature, we find that $${\text{La}}_{0.67} {\text{Ca}}_{0.23} {\text{Sr}}_{0.1} {\text{Mn}}_{0.98} {\text{Ni}}_{0.02} {\text{O}}_{3}$$ sample has a very important magnetocaloric effect (MCE). In a magnetic field variation of 5 T, this MCE is explained by a maximum of magnetic entropy change $$\left| {\Delta S_{M}^{max} } \right|$$ and a big RCP values at 4.92 $${\text{J}}.{\text{Kg}}^{ - 1} {\text{K}}^{ - 1}$$ and 145 J/kg, respectively, around room temperature (296 K), which give the possibility of technologic application in magnetic refrigeration area. In addition, we find an admirable estimate of the magnetic entropy change, which is based on the Landau theory. Finally, we use the magnetic field dependence of $$\Delta S_{M}$$ to determine the critical exponents of the system and we find that β = 0.39, γ = 1.35, and δ = 4.43, are very close to those predicted to the 3D-Heisenberg model. These results indicate that the present compound is one of candidate materials for magnetic refrigerators near room temperature.

High flux and CO2-resistance of La0.6Ca0.4Co1–xFexO3−δ oxygen-transporting membranes

Most of the currently used perovskite-based oxygen-transporting membranes have insufficient resistance towards CO2 and high material costs that potentially limit their commercial applications. In the present work, a highly CO2-tolerant oxygen permeation membrane based on La0.6Ca0.4Co1–xFexO3−δ (x = 0, 0.3, 0.5, 0.7, 1) was designed and prepared by a scalable reverse co-precipitation method. The oxygen permeation flux through the dense membranes was evaluated and found to be highly dependent on the Co/Fe ratio. La0.6Ca0.4Co0.3Fe0.7O3−δ possessed the highest permeation flux among the investigated samples, achieving 0.76 ml min−1 cm−2 under an Air/He gradient and 0.5 ml min−1 cm−2 under an Air/CO2 gradient at 1173 K for a 1 mm thick membrane. A combination study of first principles calculations and experimental measurements was conducted to advance the understanding of Co/Fe ratio effects on the oxygen migration behavior in La0.6Ca0.4Co1–xFexO3−δ. The observed oxygen permeability is three times higher than that reported in literature under similar conditions. The presented results demonstrate that this highly CO2-tolerant membrane is a promising candidate for high temperature oxygen separation applications.

Magnetic field at Ce impurities in La sites of La0.5Ba0.5MnO3 double perovskites

Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol-Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and a pure antiferromagnetic interaction below 100 K. Moreover, it also indicates an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites measured with 140Ce probe nuclei, which can be ascribed to the contribution of 4f band of Ce to Magnetic Hyperfine Field (Bhf) at low temperatures due to the increase in its localized character.