La1−xSrxMnO3 Research Articles

Magnetic and Cytotoxicity Properties of La1−xSr x MnO3(0 ≤ x ≤ 0.5) Nanoparticles Prepared by a Simple Thermal Hydro-Decomposition

This study reports the magnetic and cytotoxicity properties of magnetic nanoparticles of La1−xSrxMnO3(LSMO) withx = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 by a simple thermal decomposition method by using acetate salts of La, Sr, and Mn as starting materials in aqueous solution. To obtain the LSMO nanoparticles, thermal decomposition of the precursor was carried out at the temperatures of 600, 700, 800, and 900 °C for 6 h. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM, and SEM. Structural characterization shows that the prepared particles consist of two phases of LaMnO3(LMO) and LSMO with crystallite sizes ranging from 20 nm to 87 nm. All the prepared samples have a perovskite structure with transformation from cubic to rhombohedral at thermal decomposition temperature higher than 900 °C in LSMO samples ofx ≤ 0.3. Basic magnetic characteristics such as saturated magnetization (MS) and coercive field (HC) were evaluated by vibrating sample magnetometry at room temperature (20 °C). The samples show paramagnetic behavior for all the samples withx = 0 or LMO, and a superparamagnetic behavior for the other samples havingMSvalues of ~20–47 emu/g and theHCvalues of ~10–40 Oe, depending on the crystallite size and thermal decomposition temperature. Cytotoxicity of the synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result shows that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extract of LSMO nanoparticles.

Microwave advantages in inorganic synthesis of La0.5 Sr0.5MnO3 powders for perovskite ceramics

In this work the advantage of the use of the microwave technology was exploited for the preparation of perovskite ceramics. Microwave-assisted hydrothermal method has been applied to the preparation of strontium-doped lanthanum manganites with different stoichiometric ratio of the three oxides, La1-x SrxMnO3 (x = 0.3, 0.5, 0.6). In particular, pure black narrow dispersed crystallites of La0.5Sr0.5MnO3 of 0.68?0.18 ?m were prepared in only 45 minutes at 240?C and a KOH concentration of 21 M. The complete chemical, mineralogical and microstructural characterization of the powders reveal the same structural properties of the perovskite powders previously synthesised by ceramic and conventional hydrothermal routes. .

Thickness dependent transport properties and percolative phase separation in polycrystalline manganite thin films

The effects of film thicknesses on the electronic transport and percolative metal-insulator (M-I) transition of La1−xSrxMnO3 (LSMO) films have been investigated. The conductivity increases with the layer thickness; this is regarded as the relaxation of tensile strains and reduction in grain boundaries (fewer scattering centers) as well as shorter hopping distances, which suppresses the Jahn–Teller distortion or enhances the double exchange. It is also observed by conductive atomic force microscopy (CAFM) that metallic and insulating regions coexist in LSMO films. The domains undergo a percolative M-I transition, and TM-I observed by CAFM is consistent with the result of four-point probe measurements.

Large magnetoresistance in a manganite spin tunnel junction usingLaMnO3as the insulating barrier

A spin-tunnel-junction based on manganites, with La1 xSrxMnO3 (LSMO) as ferromagnetic metallic electrodes and the undoped parent compound LaMnO3 (LMO) as insulating barrier, is here theoretically discussed using double exchange model Hamiltonians and numerical techniques. For an even number of LMO layers, the ground state is shown to have anti-parallel LSMO magnetic moments. This highly resistive, but fragile, state is easily destabilized by small magnetic fields, which orient the LSMO moments in the direction of the field. The magnetoresistance associated with this transition is very large, according to Monte Carlo and Density Matrix Renormalization Group studies. The influence of temperature, the case of an odd number of LMO layers, and the differences between LMO and SrTiO3 as barriers are also addressed. General trends are discussed. The study of strongly correlated electronic systems (SCES) continues attracting the attention of the Condensed Matter community. These materials present complex phase diagrams that illustrates the competition which exists among phases with very different physical properties, such as d-wave superconductivity, antiferroand ferro-magnetic order, charge- and orbital-order, multiferroic behavior, and several others. Moreover, this complexity and phase competition lead to self-organized nano-scale inhomogeneities which are believed to generate giant responses, as in the famous colossal magnetoresistance (CMR) effect of the Mn-oxides known as manganites. 1

Anisotropic magnetoresistance in colossal magnetoresistive La1−xSrxMnO3 thin films

We report on magnetic field and temperature-dependent measurements of the anisotropic magnetoresistance (AMR) in epitaxial La1−xSrxMnO3 (LSMO) thin films. While in 3d ferromagnetic alloys increasing the magnetization, either by reducing the temperature or increasing the magnetic field, increases the AMR, we find that in LSMO films the AMR dependence on magnetization displays nonmonotonic behavior which becomes particularly pronounced in lightly doped compounds. We believe that this behavior is related to the inhomogeneity exhibited by these materials.

Electronic and magnetic structure ofLa0.875Sr0.125MnO3calculated by means of hybrid density-functional theory

We present the results of ab initio calculations on magnetic and electronic structures of La1�xSrxMnO3 at low doping, x =1/8. Using the B3LYP hybrid exchange-correlation functional within the framework of densityfunctional theory, we predict a ferromagnetic ground state for La0.875Sr0.125MnO3 in both the low-temperature orthorhombic and the high-temperature pseudocubic phases. This is in contrast to its parent compound LaMnO3, for which we find in agreement with experiment the layered antiferromagnetic state to be the most stable one. The calculated density of states and bond population analysis suggest a tendency of formation of half-metallic spin states in the band gap of both structures.

Ceramic Technologies for Anode-Supported Solid Oxide Fuel Cells

One of the most promising technologies for future applications of solide oxide fuel cells (SOFC)is the so-called “anode-supported” configuration: a dense yttria-stabilised zirconia (YSZ) ceramic electrolyte is deposited as a thin film over a porous Ni / YSZ cermet substrate anode, followed by a porous ceramic cathode such as La1-xSrxMnO3 (LSM). In this paper, a short review is made of the current technologies available to achieve this particular architecture, and to optimise the service behaviour. Then, alternative materials and fabrication technologies, as well as their possible impact on performance, are proposed and investigated.

Modelling of structural domains and elastic strain calculation in rhombohedral La1−x Sr x MnO3 films on (110) SrTiO3

As reported in the literature, structural domains in (110) oriented rhombohedral La1− x Sr x MnO3 (LSMO) films on (110) SrTiO3 show a pattern with alternating domain widths and inclined domain walls. An appropriate one-dimensional periodic domain model was developed and the non-uniform strain field in a coherently grown film was calculated by applying the coherency-defect approach. The strain is sharply peaked at the junction of the domain walls and the film/substrate interface. The dependence of the equilibrium domain-width ratio and domain-pattern period on film thickness was determined by minimizing the sum of elastic and domain-wall energies. The proposed domain structure can be formed only in a certain range of the film's crystal-structure data compared to the substrate. Corresponding composition-dependent structure data of LSMO are compiled.

Rectifying characteristics of La1－xSrxMnO3/TiO2(x=0.2, 0.15, 0.04) pn heterojunctions

La1-xSrxMnO3(LSMO)/TiO2 pn heterojunctions have been successfully synthesized by RF magnetron sputtering and they exhibit good rectifying properties. The diffusion potentials increase with increasing Sr concentration, which may be attributed to the increased carrier concentration. And the diffusion potential increases with decreasing measurement temperature, which may have resulted from modification of the interface electronic structure of La1-xSrxMnO3/TiO2 pn heterojunction with changing temperatures. It is worth noting that the metal-insulator (M-I) transition of LSMO can also be observed in pn heterojunctions and the increased sheet-resistance of pn heterojunctions at low temperature is related to the introduction of TiO2.

Solid Oxide Fuel Cells: Strontium-Doped Lanthanum Manganite Obtained by the Citrate Technique

Nowadays, the La1-XSrXMnO3 (LSM) is one of the most common cathodic materials used in the solid oxide fuel cells (SOFCs). The dopant strontium increases the electronic conductivity of the material, besides presents an excellent electrochemical performance, relatively good chemical and thermal stability and compatibility with solid electrolyte of ZrO2/Y2O3 (YSZ). In this work, a contribution to the study of synthesis of LSM is presented with strontium concentration of 50 mol % by the citrate technique. The powders have been characterized for various techniques, as gas absorption and adsorption, X-ray fluorescence spectroscopy, laser scattering granulometry, gas helium picnometry, scanning electron microscopy (SEM), X-ray diffractometry (XRD) and calculations of theoretical density and particle average diameter. The ceramics have been characterized by SEM and XRD. The adequate characteristics of LSM have been evaluated aiming at the use in the preparation of suspensions for cathodic thin films of SOFCs.

Observation of step-induced magnetic domain formation in La1−xSrxMnO3 thin films by photoelectron emission microscopy

Magnetic domain formation in thin films of La1−xSrxMnO3 (LSMO) with x=0.2 and 0.4 epitaxially grown on stepped SrTiO3 (001) substrates has been investigated by photoelectron emission microscopy. The magnetic domains show a stripe structure elongated along the step directions, indicating uniaxial magnetic anisotropy induced by step structures. We have also found that the magnetization of the magnetic domains is slightly meandering at domain boundaries. The existence of the additional structures suggests that the magnetic domains in LSMO films are also influenced by biaxial magnetocrystalline anisotropy. The direct observation of the magnetic domain structures suggests that the competition between the two magnetic anisotropies may play an important role in magnetic properties in LSMO films.

Angle-resolved photoemission spectroscopy of perovskite-type transition-metal oxides and their analyses using tight-binding band structure

Nowadays it has become feasible to perform angle-resolved photoemission spectroscopy (ARPES) measurements of transition-metal oxides with three-dimensional perovskite structures owing to the availability of high-quality single crystals of bulk and epitaxial thin films. In this article, we review recent experimental results and interpretation of ARPES data using empirical tight-binding band-structure calculations. Results are presented for SrVO3 (SVO) bulk single crystals and La1− x Sr x FeO3 (LSFO) and La1− x Sr x MnO3 (LSMO) thin films. In the case of SVO, from comparison of the experimental results with calculated surface electronic structure, we concluded that the obtained band dispersions reflect the bulk electronic structure. The experimental band structures of LSFO and LSMO were analyzed assuming the G-type antiferromagnetic state and the ferromagnetic state, respectively. We also demonstrated that the intrinsic uncertainty of the electron momentum perpendicular to the crystal surface is important for the interpretation of the APRES results of three-dimensional materials.

Investigation of tip-induced magnetic ripples on La0.7Sr0.3MnO3 surface

As demagnetized La1−xSrxMnO3 (LSMO) thin films are magnetized by a local magnetic field from a scanning magnetic tip without an external magnetic field, a magnetic ripple pattern appears on the LSMO surface. The magnetic ripple pattern, which consists of magnetic ripples with varying magnetic periods, is different from the conventional pattern magnetized by an external field. The magnetic ripples with longer magnetic periods have larger magnitude of magnetic moment. The magnitude linearly varies as a function of magnetic period. However, the magnitude of the remanent magnetization induced by the magnetic force microscopy tip is close to that induced by the external field.

A Non-Alkoxide Sol−Gel Method for the Preparation of Homogeneous Nanocrystalline Powders of La0.85Sr0.15MnO3

Homogeneous, nanocrystalline La1-xSrxMnO3 (LSM) powders, with x ∼ 0.15, were synthesized with the epoxide addition sol−gel method. Through this simple technique, sol−gel materials were prepared from methanolic solutions of metal chlorides without the need for alkoxides, polymeric gel agents, or elaborate reaction schemes. The gels were dried in ambient conditions, resulting in mesoporous xerogels with networked nanostructures interconnecting particulate regions. Calcination of the dried gels resulted in the crystallization of single-phase LSM by 700 °C, after decomposition of intermediate hydroxide, chloride, and oxychloride compounds. SEM analysis indicated that the calcined powders were nanocrystalline and consisted of discrete particles, free of hard agglomeration. The average crystallite size and equivalent spherical diameter determined from XRD line broadening and BET analysis, respectively, were in good agreement with the SEM results (∼100 nm). The activation energies for the electronic conductivity...

Technical Reports: Pulsed Laser Deposition and in situ Surface X-ray Diffraction at the Materials Science Beamline at the Swiss Light Source

One of the primary challenges of condensed matter physicists and materials scientists is the discovery and/or design of novel materials and their detailed characterization [1]. One can argue that this scientific odyssey began with the discovery of superconductivity in ceramic cuprates in 1984 [2], and more recently, colossal magnetoresistance in the manganates [3]. One of the consequences of this has been a concerted effort to produce high-quality thin films of systems such as YBa2Cu3O7 (YBCO), La1-xSrxMnO3 (LSMO), the ruthenates, vanadates, and other complex metal oxides, driven both by technological applications, and a desire to better understand the underlying physics of these fascinating systems.

Examining the screening limit of field effect devices via the metal-insulator transition

The electronic screening length, the distance over which an electric field is attenuated in a material, imposes a lower physical bound on the lateral size scaling of semiconductor field effect devices. Alternatives will be needed to achieve devices whose characteristic dimensions approach a nanometer. In this work, we demonstrate the atomic-scale nature of screening at high electron densities, using the polarization field of a ferroelectric oxide, Pb(Zr,Ti)O3, to electrostatically modulate the metallicity of ultrathin manganite La1−xSrxMnO3 (LSMO) films near the metal-insulator transition. Within the screening length, the transport characteristics of LSMO vary sharply at the scale of a single atomic layer.

Magnetic properties of the nonstoichiometric Sr‐doped manganites

AbstractThe chemical phase content, crystal structure, and magnetization for the doped anion‐deficient La1–xSrxMnO3–x/2 (x = 0, 0.05, 0.10, 0.20, 0.30) manganites have been studied. The samples undergo the structural phase transition from the O′‐orthorhombic to the rhombohedric unit cell at x > 0.10. As doping level and oxygen deficiency increase the samples show a number of magnetic transitions. In the region of 0.05 ≤ x ≤ 0.20 the samples are inhomogeneous ferromagnets while at x = 0.30 they are cluster spin glasses. The temperature of the magnetic moment freezing is ∼45 K. The concentration dependences of the spontaneous magnetization and coercivity as well as magnetic phase diagram have been constructed. The magnetic properties of the anion‐deficient Sr‐doped samples may be interpreted on the basis of competition of the positive Mn3+(6)–O–Mn3+(6) and negative Mn3+(5)–O–Mn3+(6) isotropic superexchange interactions and impurity phase separation models. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Rhombohedral LSMO films – a unique case of ferroelastic domain formation

AbstractFerroelastic domain formation in thin films of rhombohedral La1–xSrxMnO3 (LSMO), coherently grown on (001) or (011) oriented SrTiO3 (STO), is suggested to occur during film deposition at elevated temperatures, unlike other common perovskite films where structural phase transition and domain formation take place only during cooling. Due to a comparatively small lattice parameter misfit, the LSMO/STO system should be an ideal case for the experimental observation of domain formation without additional strain relaxation effects including misfit dislocation formation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of the magnetic anisotropy in thin films of La 1–x Sr x MnO 3 using the planar Hall effect

Thin films of the colossal magnetoresistance material La1–xSrxMnO3 (LSMO) grown on SrTiO3 substrates exhibit bi-axial magnetocrystalline anisotropy with easy axes along the [110] and [10] directions. We have recently discovered that the intrinsic biaxial magnetic anisotropy combined with a giant planar Hall effect lead to striking switching behavior in the transverse resistivity of LSMO films (Appl. Phys. Lett. 84, 2593 (2004)). Here we use this phenomenon as a sensitive tool for measuring in-plane magnetization in order to characterize the magnetic anisotropy.

Polarization Study on Doped Lanthanum Gallate Electrolyte Using Impedance Spectroscopy

Alternating current complex impedance spectroscopy studies were conducted on symmetrical cells of the type [gas, electrode/La1−xSrxGa1−yMgyO3 (LSGM) electrolyte/electrode, gas]. The electrode materials were slurry-coated on both sides of the LSGM electrolyte support. The electrodes selected for this investigation are candidate materials for solid oxide fuel cell (SOFC) electrodes. Cathode materials include La1−xSrxMnO3 (LSM), La1−xSrxCoyFe1−yO3 (LSCF), a two-phase particulate composite consisting of LSM and doped-lanthanum gallate (LSGM), and LSCF + LSGM. Pt metal electrodes were also used for the purpose of comparison. Anode material investigated was the Ni + Ce0.85Gd0.15O2 composite. The study revealed important details pertaining to the charge-transfer reactions that occur in such electrodes. The information obtained can be used to design electrodes for intermediate temperature SOFCs based on LSGM electrolytes.