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Title: Microstructure evolution and magnetoresistance of the A-site ordered Ba-doped manganites

Abstract

The microstructure, crystal structure, and magnetotransport properties of microsized and nanosized Badoped manganites have been investigated. A 'two-step' reduction-reoxidation procedure has been used to obtain nanosized ceramic manganite Nd{sub 0.70}Ba{sub 0.30}MnO{sub 3} (II). The parent microsized manganite Nd{sub 0.70}Ba{sub 0.30}MnO{sub 3} (I) was prepared by usual ceramic technology in air. Then the sample was annealed in vacuum. The grain size of the reduced sample, determined by scanning electron microscopy, decreased from {approx}5 {mu}m down to {approx}100 nm. To obtain the oxygen stoichiometry nanosized sample, the Nd{sub 0.70}Ba{sub 0.30}MnO{sub 2.60} was again annealed in air. It is established that the (I) sample is a pseudocubic perovskite, whereas (II) is tetrahedral as a consequence of Nd{sup 3+} and Ba{sup 2+} ions as well as the ordering of oxygen vacancies. The (I) sample is a ferromagnet with T{sub C} {approx} 140 K. It has metal-insulator transition at T{sub MI} {approx} 135 K and a peak of magnetoresistance {approx}50% in a field of 9 kOe. For the (II) sample, the critical points of phase transitions move to higher temperatures, T{sub C} {approx} 320 K and T{sub MI} {approx} 310 K. The magnetoresistance of the (II) sample at room temperature (T {approx} 293 K) ismore » about 7% in a field of 9 kOe. The magnetotransport properties are interpreted in the framework of the nanosized effect.« less

Authors:
; ; ; ; ;  [1];  [2]
  1. National Academy of Sciences of Belarus, Joint Institute of Solids and Semiconductor Physics (Belarus)
  2. Polish Academy of Sciences, Institute of Physics (Poland)
Publication Date:
OSTI Identifier:
21088070
Resource Type:
Journal Article
Resource Relation:
Journal Name: Semiconductors; Journal Volume: 41; Journal Issue: 5; Other Information: DOI: 10.1134/S1063782607050041; Copyright (c) 2007 Nauka/Interperiodica; Article Copyright (c) 2007 Pleiades Publishing, Ltd; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANNEALING; BARIUM COMPOUNDS; BARIUM IONS; CERAMICS; DOPED MATERIALS; GRAIN SIZE; MAGNETORESISTANCE; MANGANESE COMPOUNDS; NANOSTRUCTURES; NEODYMIUM COMPOUNDS; NEODYMIUM IONS; OXIDES; PEROVSKITE; PHASE TRANSFORMATIONS; SCANNING ELECTRON MICROSCOPY; TEMPERATURE RANGE 0065-0273 K; TEMPERATURE RANGE 0273-0400 K; VACANCIES

Citation Formats

Trukhanov, S. V., E-mail: truhanov@ifttp.bas-net.by, Lobanovski, L. S., Bushinsky, M. V., Khomchenko, V. A., Fedotova, V. V., Troyanchuk, I. O., and Szymczak, H. Microstructure evolution and magnetoresistance of the A-site ordered Ba-doped manganites. United States: N. p., 2007. Web. doi:10.1134/S1063782607050041.
Trukhanov, S. V., E-mail: truhanov@ifttp.bas-net.by, Lobanovski, L. S., Bushinsky, M. V., Khomchenko, V. A., Fedotova, V. V., Troyanchuk, I. O., & Szymczak, H. Microstructure evolution and magnetoresistance of the A-site ordered Ba-doped manganites. United States. doi:10.1134/S1063782607050041.
Trukhanov, S. V., E-mail: truhanov@ifttp.bas-net.by, Lobanovski, L. S., Bushinsky, M. V., Khomchenko, V. A., Fedotova, V. V., Troyanchuk, I. O., and Szymczak, H. Tue . "Microstructure evolution and magnetoresistance of the A-site ordered Ba-doped manganites". United States. doi:10.1134/S1063782607050041.
@article{osti_21088070,
title = {Microstructure evolution and magnetoresistance of the A-site ordered Ba-doped manganites},
author = {Trukhanov, S. V., E-mail: truhanov@ifttp.bas-net.by and Lobanovski, L. S. and Bushinsky, M. V. and Khomchenko, V. A. and Fedotova, V. V. and Troyanchuk, I. O. and Szymczak, H.},
abstractNote = {The microstructure, crystal structure, and magnetotransport properties of microsized and nanosized Badoped manganites have been investigated. A 'two-step' reduction-reoxidation procedure has been used to obtain nanosized ceramic manganite Nd{sub 0.70}Ba{sub 0.30}MnO{sub 3} (II). The parent microsized manganite Nd{sub 0.70}Ba{sub 0.30}MnO{sub 3} (I) was prepared by usual ceramic technology in air. Then the sample was annealed in vacuum. The grain size of the reduced sample, determined by scanning electron microscopy, decreased from {approx}5 {mu}m down to {approx}100 nm. To obtain the oxygen stoichiometry nanosized sample, the Nd{sub 0.70}Ba{sub 0.30}MnO{sub 2.60} was again annealed in air. It is established that the (I) sample is a pseudocubic perovskite, whereas (II) is tetrahedral as a consequence of Nd{sup 3+} and Ba{sup 2+} ions as well as the ordering of oxygen vacancies. The (I) sample is a ferromagnet with T{sub C} {approx} 140 K. It has metal-insulator transition at T{sub MI} {approx} 135 K and a peak of magnetoresistance {approx}50% in a field of 9 kOe. For the (II) sample, the critical points of phase transitions move to higher temperatures, T{sub C} {approx} 320 K and T{sub MI} {approx} 310 K. The magnetoresistance of the (II) sample at room temperature (T {approx} 293 K) is about 7% in a field of 9 kOe. The magnetotransport properties are interpreted in the framework of the nanosized effect.},
doi = {10.1134/S1063782607050041},
journal = {Semiconductors},
number = 5,
volume = 41,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • The structure and magnetic properties of the Ba-ordered state in solid solutions of manganites Ln{sub 0.70}Ba{sub 0.30}MnO{sub 3-{delta}} (Ln = Pr, Nd) with a cation ratio Ln{sup 3+}/Ba{sup 2+} >> 1 are studied experimentally. The samples are obtained by two-stage synthesis. The initial stoichiometric Ba-disordered solid solutions Ln{sub 0.70}Ba{sub 0.30}MnO{sub 3} synthesized in air according to traditional ceramic technology are characterized by the orthorhombic (Imma, Z = 4) perovskite-like unit cell and are ferromagnets with Curie temperatures T{sub C} {approx} 173 and {approx} 143 K for Pr and Nd, respectively. The average size <D> of a crystalline in the initialmore » samples is 5 {mu}m. It is found that annealing of the initial samples in a vacuum of P[O{sub 2}] = 10{sup -4} Pa leads to their separation into three phases: (1) the anion-deficient ordered LnBaMn{sub 2}O{sub 5} phase described by a tetragonal (P4/mmm, Z = 2) perovskite-like unit cell, as well as the phases (2) Ln{sub 2}O{sub 3} (P3-barm1, Z = 1) and (3) MnO (Fm3-barm, Z = 2). Reduction leads to the formation of a nanocomposite with an average crystallite size <D> = 100 nm. Anion-deficient Ba-ordered phases of LnBaMn{sub 2}O{sub 5} exhibit ferrimagnetic properties with Neel temperatures T{sub N} {approx} 113 and {approx}123 K for Pr and Nd, respectively. Annealing of anion-deficient samples in air at a moderate temperature of T = 800{sup o}C does not change the average size of the nanocrystallite, but noticeably alters their phase composition. Stoichiometric nanocomposites consist of two perovskite-like phases: (1) the Ba-deficient ordered stoichiometric phase LnBaMn{sub 2}O{sub 6}, which is described by a tetragonal (P4/mmm, Z = 2) unit cell and has the Curie temperatures T{sub C} {approx} 313 (Pr) and {approx}303 K (Nd), and (2) the Ba-disordered superstoichiometric phase Ln{sub 0.90}Ba{sub 0.10}MnO{sub 3+{delta}}, which is described by an orthorhombic (Imma, Z = 4) unit cell and has Curie temperatures T{sub C} {approx} 138 (Pr) and {approx}123 K (Nd). The two magnetic phases of the Ba-ordered nanocomposite are exchange-coupled. For the low-temperature magnetic phase, a temperature hysteresis is observed at {delta}T {approx} 22 K in a field of 10 Oe and at {delta}T {approx} 5 K in a field of 1 kOe. It is shown that states with different degrees of ordering of cations in the A sublattice can be obtained employing different technological conditions of treatment. The significant changes in the magnetic properties of Ba-ordered nanocomposites are explained on the basis of chemical phase separation taking into account the effect of compression, which is a consequence of the action of chemical (cation ordering) and external (surface tension) pressures.« less
  • Giant volume magnetostriction (GVM) is detected near the Curie temperature T{sub C} in La{sub 1-x}A{sub x}MnO{sub 3} single crystals (A = Ca, Sr, Ba, 0.1 {<=} x {<=} 0.3) and above T{sub C} in La{sub 1-x}Ag{sub y}MnO{sub 3} (x = y = 0.15, 0.2 and x = 0.2, y = 0.1) ceramics (in the latter system, giant volume magnetostriction attains a value of 6.5 x 10{sup -4} in a magnetic field of 8.2 kOe). The behavior of GVM and colossal magnetoresistance (CMR) is found to be the same: both quantities have negative values, the temperature dependences of their absolute valuesmore » pass through a peak, and the isotherms do not exhibit saturation up to the maximal measuring fields of 130 kOe. In compounds with compositions La{sub 0.7}Ba{sub 0.3}MnO{sub 3} and La{sub 0.85}Ag{sub 0.15}MnO{sub 3}, GVM and CMR were observed at room temperatures (in a magnetic field of 8.2 kOe, GVM attains values of 2.54 x 10{sup -4} and 2 x 10{sup -4} and CMR is equal to 11.6 and 11.2%, respectively). Both phenomena are attributed to the presence of a magnetic (ferromagnetic-antiferromagnetic) two-phase state in these systems, which is associated with a strong s-d exchange. It is found that the maximum value of the GVM in single crystals of La{sub 1-x}A{sub x}MnO{sub 3} (A = Ba, Sr, Ca, Ag) depends on the radius R{sub A} of cation A (it is the higher, the larger the difference |R{sub A}-R{sub LA{sup 3}{sup +}}|). The only exception is the compound with A = Ag, in which the pattern is complicated by additional defectiveness. Local disorder in the La{sub 1-x}A{sub x} sublattice, which is associated with the presence of cations with different radii, leads to a displacement of oxygen ions and to crystal lattice softening. The exchange s-d interactions in La{sub 1-x}A{sub x}MnO{sub 3} (A = Ca, Sr, Ba, Ag) are found to be comparable with electrostatic interactions ensuring the existence of the crystal; this facilitates manifestation of the GVM.« less
  • We present structural, magnetic and electrical properties of the polycrystalline A-site-deficient yttrium doped double layered manganites La{sub 1.2−x}□{sub 0.2}Y{sub x}Ca{sub 1.6}Mn{sub 2}O{sub 7} (x=0.2, 0.3 and 0.4) prepared by a solid state reaction method. The samples crystallize in the tetragonal structure with the space group I4/mmm. Doping with Y decreases the cell parameters and causes a decrease of the metal-insulator transition temperature. The same evolution with doping is also seen for the deduced Curie temperature from susceptibility curves which present a clear paramagnetic-ferromagnetic transition. The significant positive intrinsic magnetoresistance, shown in all samples, reaches 85% at 122 K under 7more » T for 0.3 doped sample and can be attributed to the suppression of spin fluctuations via aligning the spins under external magnetic field, while the extrinsic one is attributed to the inter-grain spin-polarized tunneling across the grain boundaries. The simulation of the resistivity curves in the entire temperature range show that the percolation model is suitable to fit our results. The applied magnetic field increases the density of states near the Fermi level, which is in accordance with the observed decrease of resistivity. - Graphical abstract: Resistivity and magnetoresistance of La{sub 1.2−x}□{sub 0.2}Y{sub x}Ca{sub 1.6}Mn{sub 2}O{sub 7} (x=0.2, 0.3, 0.4). Solid lines correspond to the fitting results. Display Omitted.« less
  • In this article we report our studies on the microstructure, magnetoresistance (MR) behavior, and magnetic properties of the La[sub 1[minus]x[minus]y]Ca[sub x]MnO[sub 3] system in thin-film form. By varying the values of [ital x] and [ital y] in La[sub 1[minus]x[minus]y]Ca[sub x]MnO[sub 3], we have synthesized an external- (x=0.3, y=0), an internal- (x=0, y=0.3), and a mixed-doped (x=0.2, y=0.1) system with the same Mn[sup 3+]/Mn[sup 4+] ratio. Thin films of these materials have been grown [ital in situ] on (100) LaAlO[sub 3] substrates using a pulsed-laser-deposition technique. Atomic force microscopy, x-ray diffraction and high-resolution transmission electron microscopy measurements carried out on thesemore » films have shown that the films are smooth, highly crystalline, and epitaxial on the (100) LaAlO[sub 3] substrates. Electrical resistance and magnetoresistance have been measured in the 10[endash]300 K range in magnetic fields up to 5 T using a superconducting quantum interference device magnetometer. The MR ratios (calculated using the expression, [R[sub 0][minus]R[sub H]]/R[sub H], where R[sub 0] and R[sub H] are resistances in zero and applied fields) of the La[sub 0.7]Ca[sub 0.3]MnO[sub 3] (x=0.3, y=0), La[sub 0.7]MnO[sub 3] (x=0, y=0.3), and La[sub 0.7]Ca[sub 0.2]MnO[sub 3] (x=0.2, y=0.1) films are found to be 825[percent], 700[percent], and 750[percent] at 200, 240, and 220 K, respectively. The MR ratios of these films, calculated using the expression, [R[sub 0][minus]R[sub H]]/R[sub H], are 91[percent], 87[percent], and 88[percent], respectively, at the same temperatures. The variation in the insulator-to-metal transition and the MR ratio is attributed to internal chemical pressure and vacancy localization effects. Below T[sub c]/2 (T[sub c] is paramagnetic-to-ferromagnetic transition temperature), resistance increases as T[sup 2] for La[sub 0.7]Ca[sub 0.3]MnO[sub 3] and La[sub 0.7]Ca[sub 0.2]MnO[sub 3] while it increases as T[sup 5/2] for La[sub 0.7]MnO[sub 3]. The T[sup 2] and T[sup 5/2] dependence of resistance suggests that the transport is predominantly governed by an electron[endash]electron scattering and a combination of electron[endash]electron, electron[endash]phonon, and electron[endash]magnon scattering, respectively. High-temperature resistance has been observed to be consistent with small polaron hopping conductivity for all three systems. Magnetization measurements carried out on the films show that the films have reasonably square hysteresis loops with sharp T[sub c][close quote]s. Below T[sub c]/2, the magnetization decreases as T[sup 2] for La[sub 0.7]Ca[sub 0.2]MnO[sub 3] and La[sub 0.7]MnO[sub 3], suggesting single-particle excitations in them, while it decreases as T[sup 3/2] for La[sub 0.7]Ca[sub 0.3]MnO[sub 3], representing collective oscillations in this system. [copyright] [ital 1999 American Institute of Physics.]« less
  • The effect of an exchange field on the electrical transport in thin films of metallic ferromagnetic manganites has been investigated. The exchange field was induced both by direct exchange coupling in a ferromagnet/antiferromagnet multilayer and by indirect exchange interaction in a ferromagnet/paramagnet metallic superlattice. The electrical resistance of the metallic manganite layers was found to be determined by the magnitude of the vector sum of the effective exchange field and the external magnetic field.