La0.7Sr0.3MnO3 Research Articles

Emergent quasi-two-dimensional ferromagnetic state with perpendicular magnetic anisotropy at La0.7Sr0.3MnO3/SrCuO2 interface

Due to the strong interlayer coupling between multiple degrees of freedom, oxide heterostructures usually produce distinct interfacial phases with unexpected functionalities. Here, we report on the realization of quasi-two-dimensional ferromagnetic state in ultrathin La0.7Sr0.3MnO3 (LSMO) layer down to two unit cells (u.c.), being sandwiched by the planar infinite-layer structured SrCuO2 layers (P-SCO). We find the LSMO/P-SCO interface coupling has greatly suppressed the magnetic dead layer of LSMO, resulting in an emergent interfacial ferromagnetic phase. Thus, robust ferromagnetic order can be maintained in the 2 u.c.-thick LSMO layer (∼7.7 Å), showing a Curie temperature of ∼260 K and remarkable perpendicular magnetic anisotropy. X-ray absorption spectra reveal notable charge transfer from Mn to Cu at the interface, and thus, resulted preferential d3z2−r2 orbital occupation for interfacial Mn ions plays an important role in the inducing of perpendicular magnetic anisotropy in quasi-two-dimensional LSMO layer. Our work demonstrates a unique approach for tuning the properties of oxides via an interface engineering of oxygen coordination in perovskite/infinite-layer heterostructures.

Improved catalytic activity in peroxymonosulfate activation over manganese-based perovskite oxides with acid treatment

Increasing attention has been paid to the perovskite oxides activating peroxymonosulfate (PMS) for wastewater treatment. In this article, the La0.65Sr0.35MnO3 (LSMO) treated with dilute HNO3 was explored for PMS activation. The La0.65Sr0.35MnO3/Mn3O4 composite is obtained after acid etching. The valence state of B-site Mn and surface oxygen vacancies are populated by etching different time. The LSMO-3 h (etching for 3 h) exhibits the best catalytic performance due to the activation of lattice oxygen, which induces improved redox ability. Minimal reactive oxygen species (ROS) such as OH, SO4−, 1O2, and O2− are generated, contributing little to bisphenol A (BPA) degradation. The Mn(III)-PMS complex and highly oxidative Mn(IV) under the acidic environment are responsible for the excellent degradation. The findings demonstrate an effective strategy of surface etching in enhancing the catalytic performance of perovskite oxides for advanced oxidation.

The sponge-like La0.7Sr0.3MnO3 as interface evaporation material with enhanced photothermal conversion rate

Interfacial solar steam generation (ISSG) has attracted much attention as a method that can use solar energy to efficiently produce water. However, the design and preparation of photothermal materials (PTMs) with excellent performance is still a key challenge in practical applications. In this work, we successfully prepared sponge-like La0.7Sr0.3MnO3 (LSMO) for ISSG. This sponge-like morphology is conducive to its efficient absorption of sunlight, which makes its absorptivity as high as 98.39 %. In addition, the structure of this sample and its excellent hydrophilicity together provide a good channel for water transport and evaporation. Under the 1 sun (1 kW∙m−2) irradiation, the water evaporation of sponge-like LSMO material is 1.616 kg∙m−2∙h−1, and the photothermal conversion efficiency is 94.33 %. Our work demonstrates the potential of LSMO as a PTMs in ISSG.

Enhancement of capacitance of waterproof supercapacitors by controlling the thickness of their composite electrodes (graphene/ La0.2Gd1.8Zr2O7: La0.7Sr0.3MnO3)

We report the electrochemical performance of wrinkled/washable graphene-based supercapacitors (SCs). Sustainable graphene electrodes were fabricated by printing graphene microplates on recycled plastics (taken from wasted chip-packets), which provided flexibility to the SCs. The devices made with only graphene electrodes had an energy-density/specific-capacitance of 8.8 Wh kg−1/99.1 F g−1. To enhance the electrochemical properties of the SCs, a mixture of La0.2Gd1.8Zr2O7 (LGZ) and La0.7Sr0.3MnO3 (LSM) perovskites (redox materials) were added on their electrodes. After this, the energy-density/capacitance was enhanced to 53.1 Wh kg−1/596.90 F g−1, that is, an improvement of 503/502%, respectively. Subsequently, the solid state SCs were completely rolled or wrinkled, in consequence, the capacitance decreased by 12.1 and 35.6%, respectively. Even more, the SCs were immersed in water or subjected to washing/drying cycles using a washing-machine and the capacitance barely decreased by ⁓14.2%. Additionally, the thickness of the SC electrodes was varied in the range of 65–400 μm and obtained the maximum capacitance for a thickness of 330 μm. Overall, we demonstrated that incorporating the LGZ/LSM perovskite on the SC electrodes provided extra redox centers, which incremented the capacitance of the devices. The SCs reported here are waterproof and wrinkled, thus, they could provide energy to wearable devices.

Influence of Electrode Potential on Oxygen Mobility Probed by Polarized Isotopic Exchange in Solid Oxide Electrolyser Cells: Insights for Electro‐Assisted Oxidation Reactions

AbstractOxygen mobility was studied by oxygen isotopic exchange on three electrodes used in Solid Oxide Electrolyser Cells under polarization (La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Co0.2Fe0.8O3‐δ (LSCF) and La2NiO4+δ (LNO)). The rate of the surface and the bulk mechanisms for oxygen mobility is depending on the type of conductivity (electronic conduction or mixed ionic and electronic conductivity). It is shown that a one oxygen atom exchange is dominant for the surface path whereas a two oxygen atoms mechanism dominates for the bulk path. The rate constant for the bulk path is much higher than the one for the surface path by two orders of magnitude. Additionally, polarized oxygen isotopic exchange revealed that electrode overvoltage increases significantly the rate constant for the surface path, whereas its impact on the bulk path is negligible.

Evolution of magnetic anisotropy in La0.67Sr0.33MnO3 thin films due to the appearance of out-of-plane magnetization at low temperature

We have observed quadrupolar angle-dependent anisotropic magnetoresistance (AMR) at low temperature in La0.67Sr0.33MnO3 (LSMO) films grown on SrTiO3 substrate, where the magnetic field was applied while rotating the direction of the applied magnetic field from out-of-plane (OP) to in-plane. At room temperature, the easy axis is in-plane and has a two-fold magnetic anisotropy. As the temperature decreases, it changes to a quadrupolar anisotropy. Along with the AMR, we have measured the magnetoresistance (MR) in the OP direction at various temperatures. Like the AMR, we found the appearance of a new magnetic configuration in the OP direction at low temperatures. We suggest that one of the important origins of the new OP magnetism, which appears at temperature much lower than the Curie temperature (Tc), is the d3z2−r2 orbital at the interface between the LSMO films and SrTiO3 substrate. It has been reported that despite the tensile strain imposed by the SrTiO3 substrate, the d3z2−r2 orbital exists at the interface and causes the OP magnetism. We demonstrate by a polarized x-ray resonant scattering that there is a higher density of d3z2−r2 orbitals at the interface than in the region away from the interface. As other references have proposed, we suggest the orbital reconstructions and the orbital reconstruction-driven magnetic reorientation at the interface as the origin of the appearance of the OP magnetism present in the AMR and MR results.

Mechanism insight into enhanced oxygen reduction reaction over heterovalent ion incorporated pyrochlore Pr2Zr2O7 for direct ammonia solid oxide fuel cells

An effective B-site doping strategy through heterovalent ions was developed to synthesize a series of pyrochlore Pr2Zr1.95X0.05O7+δ (PZX, X = Mn, Sc, Sn, Nb, Mo, Al, Ga, In) for the direct ammonia solid oxide fuel cell (DA-SOFC) cathode. To guide the design of efficient cathodes for DA-SOFC, we explore the relationships between the ionic radius/valence of dopant and electrochemical performance. In view of the energy matching and interaction between the dopant and the host lattice, the substitution of trivalent Sc3+ with similar ionic radius for tetravalent Zr4+ can greatly improve the oxygen reduction reaction activity of Pr2Zr2O7 due to the reduced bond energy of 48f-oxygen ions in octahedral [ZrO6] units. As a result, the anode-supported single cell Ni-YSZ|YSZ|PZSc-60YSZ yields an output power density of 0.44 and 1.45 W·cm−2 at 600 and 800 °C with ammonia fuel, outperforming PZX (X = Mn, Sn, Nb, Mo, Al, Ga, In) and common La0.8Sr0.2MnO3 (LSM)-based DA-SOFC. The detailed characterizations are employed to gain insight into the structure-activity relationship and reaction mechanism.

Strain-induced phase transition at the surface of epitaxial La0.65Sr0.35MnO3 films

The strong coupling between lattice, electron and spin systems in perovskite manganites along with symmetry breaking at interfaces could lead to inherently different electronic and structural phases at the surface of thin manganite films. To study whether the surface reconstruction can be tuned by epitaxy strain, we employed Surface-Enhanced Raman Spectroscopy (SERS) on La0.65Sr0.35MnO3 (LSMO) thin films epitaxially grown on LaAlO3 substrates. A moderate compressive strain (ε < 1 %) did not change the surface state as compared to that found in unstrained LSMO/MgO(200) films. In contrast, a strong in-plane compressive strain (2 < ε < 3.4 %) stabilizes a novel phase at the surface, characterized by a unique SERS spectrum, which reveals a phase transition at T* = 220 K accompanied by an anomalously strong hardening of the Jahn-Teller mode.

Reformation of La0.7Sr0.3MnO3 properties by using ZnO in La0.7Sr0.3MnO3-ZnO heterostructures grown on (001) oriented Si.

Study of the available density of states (DOS) close-to-zero bias for conduction in strongly correlated electron systems, such as half-metallic La0.7Sr0.3MnO3 (LSMO) and its heterostructures, is important for fundamental and application reasons. As the DOS is proportional to the differential conductance (dI/dV), the dI/dV of a 120 Å LSMO film and its reformation in LSMO/ZnO heterostructures was investigated for different ZnO thicknesses. Unlike in conventional metals, the dI/dV of LSMO exhibits a power-law dependent zero-bias anomaly, i.e., dI/dV ∝ Vm (m ∼ 1) near zero bias in the ferromagnetic metallic state at 10 K. The growth of ZnO on LSMO reforms the linear dI/dVvs. V of LSMO near zero bias to non-linear. The exponent 'm' becomes ∼0.5 for a higher ZnO thickness, revealing increased electron-electron interactions and suppression of Kondo-like, double and superexchange interactions, which are responsible for the depression of the DOS of LSMO near zero bias. In a magnetically disordered state, i.e., around the Curie temperature, ZnO reforms the linear V-shaped dI/dV vs. V of LSMO to parabolic U-shaped dI/dVvs.V and controls the electron concentrations in the t2g-orbitals of Mn realized from the DOS simulations. Additionally, ZnO introduces a peak in the dI/dV vs. V due to Fowler-Nordheim tunnelling, and the peak voltage can be tuned by varying the ZnO thickness or temperature from 300 K to 360 K. Such functions of ZnO yield major perspectives for novel applications in thin-film-based devices.

Exceptional behavior of a high-temperature superconductor in proximity to a ferromagnet in a bilayer film, La0.67Sr0.33MnO3/YBa2Cu3O7.

We studied the electronic properties of a high-temperature superconductor in proximity to a ferromagnetic material in a bilayer film of La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7 (YBCO). High-quality single-crystalline films of YBCO and LSMO/YBCO were grown epitaxially on an SrTiO3 (001) surface. Magnetization data of the LSMO/YBCO bilayer exhibit ferromagnetic transition at about 255 K, which is much smaller than the Curie temperature of bulk LSMO. Experimental data show the emergence of magnetic anisotropy with cooling, which becomes significantly stronger in the superconducting phase. The onset temperature of diamagnetism is observed at 86 K in the YBCO sample for the out-of-plane magnetization and at 89 K in the in-plane data. Interestingly, the diamagnetism sets in at about 86 K for both magnetization directions in the LSMO/YBCO film despite the presence of the ferromagnetic LSMO layer underneath. Ba 4d and Y 3d core-level spectra show different surface and bulk electronic structures. Surface contribution is reduced significantly in the LSMO/YBCO sample, suggesting enhanced bulk-like behavior due to an enhancement of electron density near the surface arising from charge transfer across the interface. These results reveal an outstanding platform for on-demand tuning of properties without affecting the superconductivity of the system for the exploration of fundamental science and applications in advanced technology.

Ultra-high resistive switching current ratio and improved ferroelectricity and dielectric tunability performance in a BaTiO3/La0.7Sr0.3MnO3 heterostructure by inserting a SrCoO2.5 layer.

A BaTiO3/SrCoO2.5 (BTO/SCO) bilayer and a BTO single film were prepared by radio frequency magnetron sputtering on La0.7Sr0.3MnO3 (LSMO) buffered SrTiO3 (001) substrates. Interestingly, compared with reported BTO-based films, the BTO/SCO/LSMO heterostructure has a maximum ON/OFF current ratio of ∼945. More interestingly, compared with the BTO single layer, a larger Pr (∼18.4 μC cm-2) and larger dielectric tunability (∼71.9%) were achieved in the BTO/SCO bilayer. The improved performance may be attributed to the large tetragonality and improved oxygen vacancy concentrations in the BTO/SCO/LSMO heterostructure. Furthermore, our BTO/SCO/LSMO stacks exhibit potential for flexible electronic informational devices.

Bending tailored conducting behavior in freestanding La0.67Sr0.33MnO3 (LSMO) film

Bending tailored conducting behavior in freestanding La0.67Sr0.33MnO3 (LSMO) film

Enhanced Electrochemical Performance of LaMnO3 Nanoparticles by Ca/Sr Doping

In this paper, the sol-gel method was used to synthesize powders of LaMnO3 (LMO), La0.85Ca0.15MnO3 (LCM), and La0.85Sr0.15MnO3 (LSM). The effect of substituting Ca and Sr at the A-site on the perovskite crystal structure and electrochemical capabilities of LMO was investigated. LCM retained its orthogonal structure in comparison to the parent LMO components, whereas LSM transitioned to a rhombic structure. At 0.5 A/g, the specific capacitance of LCM and LSM electrodes is 185.5 F/g and 248 F/g, respectively. The specific capacitance of LCM was three times greater than that of the LMO electrode. Among the three samples (LMO, 22.25 m2 g−1; LSM, 31.56 m2 g−1), the LCM sample exhibited the highest specific surface area of 38.79 m2 g−1. The charge transfer resistances of the LMO, LCM, and LSM are 0.48 Ω, 0.36 Ω, and 0.38 Ω, respectively. The LCM electrode exhibits the greatest capacitance performance due to its more refined morphology, increased concentration of oxygen vacancy, and more complete utilization of the perovskite bulk structure. The above results demonstrate that Ca or Sr substitution of A-site compounds has great potential for supercapacitor applications.

Electrical transport mechanism of manganite-based trilayer heterostructures in the Cusp and insulating regions

In the present study, efforts are made to study the temperature dependent resistivity (ρ-T) variations of manganites (La0.7Sr0.3MnO3 (LSMO) single layer) and manganites-based systems ((LSMO/γ-Fe2O3/LSMO) trilayer heterostructures) in two distinct regions (Cusp region and Insulating region). Cusp region is an intermediate region between Metallic region and Insulating region. The resistivity-temperature curves are studied and analysed by various resistive models and fitting equations. The co-existence of ferromagnetic clusters and polarons manifests in the Cusp region. The Insulating region is explored and fitted under two regimes: Low Temperature Insulating region and High Temperature Insulating region. Various mathematical models viz. Thermal Activation model, Small Polaron Hopping model and Variable Range Hopping model were employed to study the ρ-T variations under various temperature ranges for LSMO (60 nm) single layer system and LSMO/γ-Fe2O3/LSMO (150 nm) trilayer heterostructures. In Insulating region, the deviations in the fitted curves from the experimental data is due to intrinsic disorder at the R/A site in case of LSMO single layer system while in case of trilayer system disorder exists at both R/A and B sites. The study is crucial to understand the microscopic picture of electrical transport behavior in both the systems near and above Metal-Insulator Transition.

Pseudocapacitive ferromagnetic polypyrrole – La0.8Sr0.2MnO3 composites

1-Diazo-2-naphthol-4-sulfonic acid (DNS), and sodium taurocholate (ST) are used as new anionic dopants-dispersants for the fabrication of polypyrrole (PPy) supercapacitor electrodes. The electrodes show ideal pseudocapacitive behavior with capacitances of 4.89 and 4.77 F cm−2 for DNS and ST, respectively. Composites with high active mass of 40 mg cm−2 containing ferromagnetic La0.8Sr0.2MnO3 (LSM) and conductive PPy are obtained. The approach of this investigation eliminates the problems of previous works on PPy-LSM composites related to the use of negative potential window and alkaline electrolyte. In contrast to previous works, the electrodes showed nearly ideal pseudocapacitive behavior in a neutral Na2SO4 electrolyte. Moreover, the composite electrodes showed significantly higher capacitances of 2.82 and 2.60 F cm−2 for DNS and ST, respectively, and enhanced capacitance retention at high charging rates. The composites combine advanced pseudocapacitive properties of PPy with high magnetization of ferromagnetic LSM.

Terahertz inverse spin Hall effect in spintronic nanostructures with various ferromagnetic materials

Bilayers of ferromagnetic and heavy metal nanolayers excited with femtosecond laser pulses emit subpicosecond bursts of electromagnetic radiation with spectral frequencies up to several THz. We fabricated such spintronic THz emitters containing various ferromagnetic materials with vastly different magnetic remanence, saturation magnetization, and coercive fields. In all cases, the THz amplitude versus magnetic-field dependence follows the independently measured magnetization hysteresis loops and the THz polarization direction is perpendicular to the sample’s magnetization M, both consistent with the inverse spin Hall effect (ISHE) as the physical origin. The mV-level signals of observed THz transients also favor the ISHE over the anomalous Nernst effect (ANE). The M(T) variation governs the temperature dependence of the THz generation. Emitters with weakly remanent ferromagnets are magnetic-field tunable, while moderately and strongly remanent ferromagnets, once magnetized, allow intense THz generation even without an external field, nevertheless exhibiting low susceptibility to magnetic perturbations if the hysteresis loop is square. Hence, exploiting the magnetic properties of the ferromagnetic layer enables tailoring of weakly temperature-dependent spintronic THz emitters. Finally, we explored the applicability of perovskite oxide materials such as La-Sr-Mn-O (LSMO) for THz transient generation. We detected weak (<40-µV amplitude) THz emissions from both LSMO/Au and pure LSMO nanostructures with no sign flip upon the sample reversal. Thus, we excluded the ISHE and believe it was likely governed by the ANE in the thick-film regime, although we cannot exclude the transient demagnetization mechanism.

Impact of Twin's Landscape on the Magnetic Damping of La2/3Sr1/3MnO3 Thin Films

AbstractUnderstanding the origin and mechanisms of magnetic damping in complex oxide materials is crucial for optimizing spin dynamics and tailoring their properties for specific spintronic applications. Ferromagnetic resonance spectroscopy (FMR) technique has been used to investigate the magnetic damping of multiple La2/3Sr1/3MnO3 (LSMO) epitaxial thin films with similar thickness and identical DC magnetic properties. However, the dynamic magnetic properties exhibit noticeable variations among samples. Microstructural analyses using X‐ray diffraction (XRD) and atomic force microscopy (AFM), confirm that the samples are structurally identical, except for minute differences in the miscut angles of the substrates. Nevertheless, when examining the samples using backscattered electron (BSE) images in scanning electron microscopy (SEM), significant disparities in the twin distribution are observed. These variations in the twin distribution directly correlate with the observed differences in the damping values. A careful image analysis of BSE images allows to demonstrate that the increase of damping is due to the pinning of the magnetization in the twin boundaries.

Magneto-optical tunability of impedance through electronic structure modification in ZnO–rGO/LSMO/ITO spintronic devices

In this paper, we have investigated red light (∼660 nm) and magnetic field dependence of impedance across (100−x)% ZnO(zinc oxide)–x% rGO(reduced graphene oxide)/La0.7Sr0.3MnO3(LSMO)/ITO (x=0,0.6,0.8,100) heterostructure devices. Field-induced scattering due to the spin filter effect and spin polarized tunneling (SPT) have been extracted from the zinc oxide–reduced graphene oxide nanocomposite/LSMO space charge region (ZnO–rGO/LSMO SCR) and the LSMO active region of the devices, respectively. Higher SPT leads to higher LSMO SCR scattering across the devices. Devices with higher rGO contents could not be fitted with two RC circuits as resistance values because the two phenomena are incomparable with each other. Light-induced scattering has been observed at the ZnO–rGO nanocomposite active region and ZnO–rGO/LSMO SCR of the devices. For composite devices with x=0.8 and 0.6, higher photocarrier generation at ZnO–rGO nanocomposite active layer leads to enhanced scattering at LSMO SCR with light illumination. Light-dependent scattering at both regions, however, follows almost same decreasing trend for bare devices with x=0, 100. The decreasing trend of light-dependent scattering for ZnO/LSMO/ITO and rGO/LSMO/ITO bare devices suddenly gets reversed and, eventually, follows an increasing trend at magnetic field ambiance of 0.5 and 1 kOe, respectively. The LSMO SCRs of the bare devices got enhanced with the field, leading to a light-dependent response similar to composite devices at the higher field.

Magnetic coupling mechanism of the interface in Bi2Se3/La0.7Sr0.3MnO3

The magnetic proximity effect in Bi2Se3 (BS)/La0.7Sr0.3MnO3 (LSMO) heterostructures is studied by first-principles calculations based on the density functional theory (DFT). Two heterogeneous structures LSMO (La, Sr, O termination layer, labeled as LaSrO)/BS and LSMO (Mn, O termination layer, labeled as MnO2)/BS are configured. In the LaSrO/BS system, the larger interfacial distance (2.88 Å) and higher interfacial binding energy (−6.36 eV) indicate a greater degree of stability for this structure. The spin polarization density distribution and spin magnetic moment results show BS can be effectively magnetized in both heterostructures. The magnetic coupling effect and observed charge transfer in MnO2/BS are more pronounced, suggesting potential differences in the magnetic exchange mechanisms between LaSrO/BS and MnO2/BS. The projected density of states (PDOS) and spin polarizability suggest that electron exchange and orbital hybridization between Mn-3d orbitals and BS play a crucial role in inducing magnetic order in BS. In MnO2/BS, the magnetic proximity effect is stronger, and more spin electron transfer between Mn-d and Se-p orbital of BS. These results may promote the application of TIs in the spintronic devices field.

Unveiling the red electroluminescence in LSMO-SRO thin film heterostructures

Herein, intense red electroluminescence (674 nm) in a La0.7Sr0.3MnO3(LSMO)-SrRuO3(SRO) thin films heterostructure obtained by RF-magnetron sputtering is reported for the first time. This novel phenomenon may open a new door in the field of optoelectronics and new generation devices based on multiferroic heterostructure. The structural properties were analyzed using grazing incidence x-ray diffraction demonstrating a rhombohedral structure for LSMO with (024) preferential orientation and an orthorhombic structure for SRO films with (121) preferential orientation. Raman and x-ray photoelectron spectroscopy (XPS) results demonstrated a mix of phases present in LSMO thin films. The thickness analysis was performed using scanning electron microscopy (SEM) in cross section and the thickness was found to be 123 nm and 49 nm for LSMO and SRO, respectively. XPS analysis for LSMO revealed that point defects associate to Mn cations and oxygen vacancies modify the total electrical conductivity and due to Mott transitions, suggest a p-type semiconductor behavior. For the SRO film, the XPS analysis demonstrated a change in the stoichiometry of the film surface, which provides a large amount of oxygen vacancies indicating a metal oxide transition with effects that involve multiple degrees of freedom (charge, spin, and lattice). The electrical behavior observed in the heterostructure corresponds to a metal-semiconductor junction showing a Schottky conduction mechanism in positive bias and a space charge limited conduction mechanism in negative bias. The red electroluminescence effect is discussed considering both a radiative recombination process occurred at the interface due to the presence of Mn2+ ions and an energy transfer mechanism assisted by the migration of the high amount of oxygen vacancies present in the interface.