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Title: Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}

Abstract

Nanopowder of ferromagnetic La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) and multiferroic BiFeO{sub 3} (BFO) were synthesized by spray pyrolysis method. Different compositions of multiferroic xLSCO-(1−x)BFO composites were synthesized at 800 °C for 2 h. Scanning electron microscopy and energy dispersive spectroscopy elemental mapping were performed to study the morphology of composites. Ferri/ferromagnetic responses above T{sub C} (LSCO) are observed, which are associated with the interfaces LSCO/BFO. This interface presents a different behavior compared to the original perovskites, and the magnitude of the magnetization depends on x. Electrical DC conductivity as a function of temperature for LSCO nanopowder (x = 1) presents a different behavior than that reported in bulk material. For x = 1 and 0.9, the model by Glazman and Matveev [Zh. Eksp. Teor. Fiz. 94, 332 (1988)] is proposed to describe the electrical conductivity. On the other hand, x = 0, 0.1, and 0.5 present a variable range hopping behavior. Complex impedance spectroscopy as a function of frequency indicates a pure resistive behavior for x ≥ 0.5 compositions, while a complex resistive-capacitive behavior is observed for low x values (0, 0.1). In these samples, low values of magnetoelectric coupling were measured with an AC lock-in technique.

Authors:
; ;  [1];  [2]
  1. Centro Atómico Bariloche, Comisión Nacional de Energía Atómica, CONICET and Instituto Balseiro, Universidad Nacional de Cuyo, 8400 San Carlos de Bariloche, RN (Argentina)
  2. INTEQUI, Universidad Nacional de San Luis, CONICET, Área de Química General e Inorgánica “Dr. G.F.Puelles”- Facultad de Química, Bioquímica y Farmacia, Chacabuco y Pedernera, 5700 San Luis (Argentina)
Publication Date:
OSTI Identifier:
22598902
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 7; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COMPARATIVE EVALUATIONS; COUPLING; ELECTRIC CONDUCTIVITY; FERROMAGNETIC MATERIALS; FREQUENCY DEPENDENCE; IMPEDANCE; INTERFACES; MAGNETIC PROPERTIES; MAGNETIZATION; MAPPING; MORPHOLOGY; NANOSTRUCTURES; PEROVSKITE; POWDERS; PYROLYSIS; SCANNING ELECTRON MICROSCOPY; SPECTROSCOPY; TEMPERATURE DEPENDENCE

Citation Formats

Lohr, Javier H., Saleta, Martín E., Sánchez, Rodolfo D., E-mail: rodo@cab.cnea.gov.ar, and López, Carlos A. Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}. United States: N. p., 2016. Web. doi:10.1063/1.4960697.
Lohr, Javier H., Saleta, Martín E., Sánchez, Rodolfo D., E-mail: rodo@cab.cnea.gov.ar, & López, Carlos A. Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}. United States. doi:10.1063/1.4960697.
Lohr, Javier H., Saleta, Martín E., Sánchez, Rodolfo D., E-mail: rodo@cab.cnea.gov.ar, and López, Carlos A. Sun . "Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}". United States. doi:10.1063/1.4960697.
@article{osti_22598902,
title = {Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}},
author = {Lohr, Javier H. and Saleta, Martín E. and Sánchez, Rodolfo D., E-mail: rodo@cab.cnea.gov.ar and López, Carlos A.},
abstractNote = {Nanopowder of ferromagnetic La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) and multiferroic BiFeO{sub 3} (BFO) were synthesized by spray pyrolysis method. Different compositions of multiferroic xLSCO-(1−x)BFO composites were synthesized at 800 °C for 2 h. Scanning electron microscopy and energy dispersive spectroscopy elemental mapping were performed to study the morphology of composites. Ferri/ferromagnetic responses above T{sub C} (LSCO) are observed, which are associated with the interfaces LSCO/BFO. This interface presents a different behavior compared to the original perovskites, and the magnitude of the magnetization depends on x. Electrical DC conductivity as a function of temperature for LSCO nanopowder (x = 1) presents a different behavior than that reported in bulk material. For x = 1 and 0.9, the model by Glazman and Matveev [Zh. Eksp. Teor. Fiz. 94, 332 (1988)] is proposed to describe the electrical conductivity. On the other hand, x = 0, 0.1, and 0.5 present a variable range hopping behavior. Complex impedance spectroscopy as a function of frequency indicates a pure resistive behavior for x ≥ 0.5 compositions, while a complex resistive-capacitive behavior is observed for low x values (0, 0.1). In these samples, low values of magnetoelectric coupling were measured with an AC lock-in technique.},
doi = {10.1063/1.4960697},
journal = {Journal of Applied Physics},
number = 7,
volume = 120,
place = {United States},
year = {Sun Aug 21 00:00:00 EDT 2016},
month = {Sun Aug 21 00:00:00 EDT 2016}
}
  • The series of La{sub 1{minus}x}Sr{sub x}CoO{sub 3{minus}{delta}} (0.5 {le} x {le} 0.9) perovskites have been prepared using the Pechini gel technique. The products were chemically oxidized by stirring in a sodium hypobromite solution. The samples have been characterized by powder X-ray diffraction, thermal analysis, iodometric titration, Co K edge X-ray absorption spectroscopy, temperature-dependent SQUID magnetic susceptibility, and temperature-dependent electrical resistivity. The Sr-rich samples (x > 0.7) have the brownmillerite-type structure prior to oxidation and the cubic perovskite structure after treatment with sodium hypobromite. Iodometric titration shows as much as a {approximately}14% increase in Co(IV) concentration in the Sr-rich samples aftermore » chemical oxidation. The Co K edge spectra show that there is very little change in the formal cobalt valence with increasing Sr content. The effective magnetic moments of the oxidized compounds level off with increasing Sr concentration. All of the chemically oxidized samples exhibit small-bandgap semiconducting behavior. The data lead to the postulation of an equilibrium between Co(IV) and O{sup {minus}} in the series.« less
  • Compositionally-graded (Ba{sub 1-x}Sr{sub x})TiO{sub 3} (BST) epitaxial thin films (with x decreasing from 0.25 to 0.0) were deposited by pulsed laser deposition on (100)LaAlO{sub 3} (LAO) single-crystal substrates covered with a conductive La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) layer as a bottom electrode. X-ray and electron diffraction patterns demonstrate that the entire graded film has a single-crystal cubic structure. The epitaxial relationship between BST, LSCO, and LAO can be described as (100){sub BST} parallel (100){sub LSCO} parallel (100){sub LAO}; [001]{sub BST} parallel [001]{sub LSCO} parallel [001]{sub LAO}. Cross-sectional transmission electron microscopy (TEM) images reveal that both the BST films and themore » LSCO bottom electrodes have sharp interfaces and overall uniform thickness across the entire specimen, and that they grow with a columnar structure. Planar TEM images show that the graded films exhibit granular and/or polyhedral morphologies with an average grain size of 50 nm. High-resolution TEM images reveal aligned rectangular-shaped voids in the graded BST film, with length size of 12-17 nm, and width of 5-8 nm along the <001> direction in the (100) plane.« less
  • Oxygen-deficient ferrates with the cubic perovskite structure Sr{sub x}Y{sub 1−x}FeO{sub 3−δ} were prepared in air (0.71≤x≤0.91) as well as in N{sub 2} (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3−δ=2.79(2) for x=0.75 to 3−δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79}more » reveal a modulation along 〈1 0 0〉{sub p} with G± ∼0.4〈1 0 0〉{sub p} indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm/K in air at 298–673 K. At 773–1173 K TEC increases up to 17.2 ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr{sub 0.75}Y{sub 0.25}Fe{sub 1−y}M{sub y}O{sub 3−δ} (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79}. Only M=Ni has increased electrical conductivity compared to un-doped Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79}. - Graphical abstract: Oxygen-deficient ferrates with the cubic perovskite structure Sr{sub x}Y{sub 1−x}FeO{sub 3−δ} were prepared both in air (0.71≤x≤0.91) and N{sub 2} (x=0.75 and 0.79) at 1573 K. Refinement of the crystal structure of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} using TOF neutron powder diffraction (NPD) data (S.G. Pm-3m, a=3.86455(3) Å; χ{sup 2}=6.71, R{sub p}=0.03; R{sub wp}=0.04) confirmed the cubic perovskite structure. The observed high anisotropic atomic displacement parameter for the oxygen atom indicates a substantial anion sublattice disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr{sub 0.75}Y{sub 0.25}FeO{sub 2.79} show compositional modulation along 〈1 0 0〉{sub p} with G± ∼0.4〈1 0 0〉{sub p} indicating ordering of oxygen vacancies at the local scale. Highlights: ► Cubic perovskites Sr{sub x}Y{sub 1−x}FeO{sub 3−δ} (0.71≤x<0.91) were synthesized. ► Sr{sub 0.75}Y{sub 0.25}Fe{sub 1−y}M{sub y}O{sub 3−δ}, M=Cr, Mn, Ni were prepared. ► High-temperature conductivity properties and crystal structure were studied. ► High-temperature thermal expansion behavior was investigated.« less
  • Heterostructured oxide interfaces created by decorating Ruddlesden-Popper phases (A2BO4) or perovskites on perovskites have shown not only pronounced cation segregation at the interface and in the A2BO4 structure but also much enhanced kinetics for oxygen electrocatalysis at elevated temperatures. In this study, we report and compare the time-dependent surface exchange kinetics and stability of (La 0.5Sr 0.5) 2CoO 4 -decorated (LSC 214) La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ (LSCF 113) and La 0.8Sr 0.2CoO 3-δ (LSC 113) thin films. While LSC 214 decoration on LSC 113 greatly reduced the degradation in the surface exchange kinetics as a function of timemore » relative to LSC 113, LSCF 113 with LSC 214 coverage showed comparable surface exchange kinetics and stability to LSCF 113. This difference can be explained by greater surface stability of LSCF 113 than LSC 113 under testing conditions, and that LSC 214 decoration on LSC 113 reduced the decomposition of LSC 113 to form secondary phases that impedes oxygen exchange kinetics, and thus resulted in enhanced stability. This hypothesis is supported by the observations that annealing at 550 °C led to the formation of Sr-rich secondary particles on LSC 113 while no such particles were observed on LSCF 113. Density functional theory (DFT) computation provides further support, which revealed greater capacity of surface Sr segregation for LSCF 113 having SrO termination than LSC 113 having (La 0.25Sr 0.75)O termination for the experimental conditions, and lower energy gain to move Sr from LSCF 113 into LSC 214 relative to the LSC 214-LSC 113 system.« less
  • We studied electrical transport in La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LCMO) and La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) nanocrystals over a temperature range of 0.4 K ≤ T ≤ 5 K. In both samples, two distinct behaviors of the conductivity are observed. For T>1 K, the variable range hopping regime is observed in LCMO sample with enhancement of the relative permittivity. In contrast, this behavior is not consistent with the extracted parameters in LSCO sample. For T<1 K, the transport is believed to occur through the metallic droplets connected to the intergranular regions where the negative magnetoresistance is due to spin-polarized tunnelingmore » phenomenon.« less