Showing papers on "Colossal magnetoresistance published in 2004"
TL;DR: The perovskites and their related structures exhibit several features of technical as well as fundamental interest, such as oxide-ion conduction with/without electronic conduction, oxidation catalysis, ferroic displacements in classic and relaxor ferroelectrics, half-metallic ferromagnetism and high-temperature superconductivity.
Abstract: The perovskites and perovskite-related structures exhibit several features of technical as well as fundamental interest. Technically useful properties include oxide-ion conduction with/without electronic conduction, oxidation catalysis, ferroic displacements in classic and relaxor ferroelectrics, half-metallic ferromagnetism and high-temperature superconductivity. Of more fundamental interest is the ability to tune, by chemical substitution on the large-cation subarray, transition-metal oxides through the crossover on the transition-metal array from localized dn configurations to itinerant d-electron behaviour without/with changing the valence state of that array. The localized-electron configurations may exhibit cooperative Jahn–Teller distortions that introduce anisotropic exchange interactions. At crossover, bond-length fluctuations may segregate into an ordered array of alternating covalent and ionic bonding in a single-valent perovskite; multicentre polarons or correlation bags may replace small polarons in a mixed-valent system. Bond-length fluctuations at crossover give vibronic conduction and suppression of the phonon contribution to the thermal conductivity; the fluctuations may order, to give high-temperature superconductivity, or transform to quantum–critical-point behaviour at lowest temperatures. Crossover of σ-bonding electrons in the presence of localized spins associated with π-bonding electrons gives rise to the colossal magnetoresistance phenomenon above a ferromagnetic Curie temperature.
534 citations
TL;DR: It is shown that the texturing can be due to the intrinsic complexity of a system with strong coupling between the electronic and elastic degrees of freedom, which leads to local energetically favourable configurations and provides a natural mechanism for the self-organized inhomogeneities over both nanometre and micrometre scales.
Abstract: The coexistence of distinct metallic and insulating electronic phases within the same sample of a perovskite manganite1,2,3,4,5,6, such as La1-x-yPryCaxMnO3, presents researchers with a tool for tuning the electronic properties in materials. In particular, colossal magnetoresistance7 in these materials—the dramatic reduction of resistivity in a magnetic field—is closely related to the observed texture owing to nanometre- and micrometre-scale inhomogeneities1,2,3,4,5,6,8. Despite accumulated data from various high-resolution probes, a theoretical understanding for the existence of such inhomogeneities has been lacking. Mechanisms invoked so far, usually based on electronic mechanisms and chemical disorder9,10,11, have been inadequate to describe the multiscale, multiphase coexistence within a unified picture. Moreover, lattice distortions and long-range strains12,13 are known to be important in the manganites14. Here we show that the texturing can be due to the intrinsic complexity of a system with strong coupling between the electronic and elastic degrees of freedom. This leads to local energetically favourable configurations and provides a natural mechanism for the self-organized inhomogeneities over both nanometre and micrometre scales. The framework provides a physical understanding of various experimental results and a basis for engineering nanoscale patterns of metallic and insulating phases.
483 citations
TL;DR: It is shown that in charge-ordered and orbitally ordered perovskites it is possible to make use of the coupling between magnetic and charge ordering to obtain ferroelectric magnets.
Abstract: Transition metal oxides with a perovskite-type structure constitute a large group of compounds with interesting properties. Among them are materials such as the prototypical ferroelectric system BaTiO(3), colossal magnetoresistance manganites and the high-T(c) superconductors. Hundreds of these compounds are magnetic, and hundreds of others are ferroelectric, but these properties very seldom coexist. Compounds with an interdependence of magnetism and ferroelectricity could be very useful: they would open up a plethora of new applications, such as switching of magnetic memory elements by electric fields. Here, we report on a possible way to avoid this incompatibility, and show that in charge-ordered and orbitally ordered perovskites it is possible to make use of the coupling between magnetic and charge ordering to obtain ferroelectric magnets. In particular, in manganites that are less than half doped there is a type of charge ordering that is intermediate between site-centred and bond-centred. Such a state breaks inversion symmetry and is predicted to be magnetic and ferroelectric.
342 citations
TL;DR: This work considers the cooperative nature of the Mn-oxide lattice distortions and induces power-law correlations in the quenched disorder used in toy models with phase competition, qualitatively modifying previous scenarios and solving the puzzle.
Abstract: Previous theoretical investigations of colossal magnetoresistance (CMR) materials explain this effect using a "clustered" state with preformed ferromagnetic islands that rapidly align their moments with increasing external magnetic fields. While qualitatively successful, explicit calculations indicate drastically different typical resistivity values in two- and three-dimensional lattices, contrary to experimental observations. This conceptual bottleneck in the phase-separated CMR scenario is resolved here considering the cooperative nature of the Mn-oxide lattice distortions. This effectively induces power-law correlations in the quenched disorder used in toy models with phase competition. When these effects are incorporated, resistor-network calculations reveal very similar results in two and three dimensions, qualitatively modifying previous scenarios and solving the puzzle.
182 citations
TL;DR: In this article, the authors trace how the ground state evolves with doping and give a self-consistent analysis of various thermodynamic, optical and transport properties of metallic manganites, isotope effect, etc.
150 citations
TL;DR: In this article, the magnetoresistance effect of Zn-Ni ferrites was investigated and it was found that the magnetoregressive effect increases as the Ni content increases in Zn1−xNixFe2O4 up to x=0.2 and then again decreases and finally becomes negligible for x=1.0.
Abstract: Spinel-type ferrites are widely used in practical applications. A fascinating property of Zn-Ni ferrites which reveals a direction for application is reported. A large negative magnetoresistance effect has been observed in ZnFe2O4 and Ni substituted Zn1−xNixFe2O4 ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature and a spin (cluster) glass transition was found for some compositions at low temperatures. The magnetoresistance is either parabolic or linear with respect to applied field up to 9 T depending on the compositions and temperatures. It was found that the magnetoresistance effect increases as the Ni content increases in Zn1−xNixFe2O4 up to x=0.2 and then again decreases and finally become negligible for x=1.0, i.e., NiFe2O4. This magnetoresistance effect can be explained with the help of spin-dependent scattering and the Yafet-Kittel angle of the Ni-substituted Zn-Ni ferrites.
117 citations
TL;DR: A new two band model with strong correlations and a dynamical mean-field theory calculation of equilibrium and transport properties are described that explain the insulator metal transition and colossal magnetoresistance quantitatively, as well as other consequences of two state coexistence.
Abstract: The persistent proximity of insulating and metallic phases, a puzzling characteristic of manganites, is argued to arise from the self-organization of the twofold degenerate e(g) orbitals of Mn into localized Jahn-Teller (JT) polaronic levels and broad band states due to the large electron-JT phonon coupling present in them. We describe a new two band model with strong correlations and a dynamical mean-field theory calculation of equilibrium and transport properties. These explain the insulator metal transition and colossal magnetoresistance quantitatively, as well as other consequences of two state coexistence.
112 citations
TL;DR: In this article, a hydrothermal synthesis of single-crystalline nanocubes composed of lanthanum barium manganite (La1-xBaxMnO3) with three different doping levels (x = 0.3, 0.5, and 0.6) was reported.
Abstract: We report a hydrothermal synthesis of single-crystalline nanocubes composed of lanthanum barium manganite (La1-xBaxMnO3) with three different doping levels (x = 0.3, 0.5, and 0.6). The synthesis yields clearly faceted nanocubes with a pseudo-cubic perovskite structure. Typical nanocubes have sizes ranging between 50 and 100 nm irrespective of doping level. Magnetic measurements performed on nanocube ensembles show that the magnetic properties depend on the doping level. The ability to synthesize nanoscale manganites of a desired doping level should enable detailed investigations of the size-dependent evolution of magnetism, colossal magnetoresistance, and nanoscale phase separation.
99 citations
TL;DR: In this article, a Co-ZnO inhomogeneous magnetic semiconductor thin films were synthesized on the subnanometer scale by sputtering and the mechanism for large negative magnetoresistance was discussed.
Abstract: Co–ZnO inhomogeneous magnetic semiconductor thin films were synthesized on the subnanometer scale by sputtering. Room temperature ferromagnetism with high magnetization was found. Large negative magnetoresistance of 11% was found at room temperature, and its value increased with a decrease in temperature up to 36% at 4.8 K. The mechanism for large negative magnetoresistance is discussed.
95 citations
TL;DR: In this paper, double perovskites of composition A 2 FeMoO 6− δ (A, alkali earths) have been prepared by soft-chemistry procedures, followed by annealing under reducing conditions (H 2 /N 2 flow).
Abstract: Double perovskites of composition A 2 FeMoO 6− δ (A, alkali earths) have been prepared by soft-chemistry procedures, followed by annealing under reducing conditions (H 2 /N 2 flow). These materials are half metallic ferromagnets, well known for their colossal magnetoresistance properties. The samples have been characterized by X-ray diffraction; temperature-programmed oxidation, specific surface measurements and XPS. The Sr compound, of tetragonal symmetry, exhibits a significant amount of oxygen vacancies, as assessed by TPO. The materials have been tested as catalysts for methane oxidation. At moderate temperatures, a significantly higher catalytic activity is observed for the Sr double perovskite, for which a 80% of conversion is reached at 800 K; by contrast the Ca and Ba materials are found to display much poorer characteristics, hardly achieving 50% of conversion rate at 1000 K. The much superior characteristics of Sr 2 FeMoO 6− δ are believed to be related to the presence of oxygen vacancies in the crystal structure.
85 citations
TL;DR: In this paper, the authors review different methods of accommodating the stress induced by the substrate: elastically, through interface dislocations, through pseudo-periodic twinning, through formation of antiphase domains or through a phase transition in the film.
Abstract: Most manganites exhibiting colossal magnetoresistant properties are structurally very simple. They are based on a perosvskite structure with the general formula . The electric and magnetic properties strongly depend on the composition (A, A', x) and eventually on the exact oxygen content. These changing properties are strongly related to structural and microstructural changes. Indeed, the structure has many degrees of freedom. The MnO6 octahedra can not only deform, they can also rotate along their fourfold or twofold axis, giving rise to different superstructures or modulated structures. This will lower the symmetry of the structure from cubic to orthorhombic, rhombohedral or monoclinic. A lowering in symmetry will of course introduce different orientation variants (twins) and translation variants (antiphase boundaries). These microstructural changes are reviewed here through a transmission electron microscopy study of bulk as well as thin film colossal magnetoresistance materials.For thin films grown on a single crystal substrate the misfit with the substrate is another very important parameter, which determines the structure and the microstructure. We review different methods of accommodating the stress induced by the substrate: elastically, through interface dislocations, through pseudo-periodic twinning, through formation of antiphase domains or through a phase transition in the film.
TL;DR: In this paper, a positive colossal magnetoresistance (CMR) was discovered in an epitaxial multilayer p-n heterostructure fabricated with Sr-doped LaMnO3 and Nb-Doped SrTiO3 by laser molecular-beam epitaxy.
Abstract: A positive colossal magnetoresistance (CMR) has been discovered in an epitaxial multilayer p–n heterostructure fabricated with Sr-doped LaMnO3 and Nb-doped SrTiO3 by laser molecular-beam epitaxy. In contrast to the negative CMR of the LaMnO3 compound family, positive CMR is observed in the temperature range from 100 to 300 K. The largest value of the magnetoresistance (MR) ratio (ΔR/R0,ΔR=RH−R0), 517%, is one order of magnitude larger than that of simple p–n junctions of the same materials previously reported. A very large MR ratio, 297%, remains in a low field of 0.01 T. Even at a temperature as high as 300 K, a MR ratio as large as 17.3% is still observed.
TL;DR: In this paper, an all-perovskite ferroelectric field effect transistor with a Pb(Zr0.2Ti0.8)O3 gate and a colossal magnetoresistive La 0.8Ca 0.2MnO3 (LCMO) channel has been successfully fabricated by pulsed-laser deposition on Si.
Abstract: An all-perovskite ferroelectric field-effect transistor with a ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) gate and a colossal magnetoresistive La0.8Ca0.2MnO3 (LCMO) channel has been successfully fabricated by pulsed-laser deposition on Si. A clear and square channel resistivity hysteresis loop, commensurate with the ferroelectric hysteresis loop of PZT, is observed. A maximum modulation of 20% after an electric field poling of 1.5×105 V/cm, and 50% under a magnetic field of 1 T, are achieved near the metal-insulator transition temperature of the LCMO channel. A data retention time of at least one day is measured. The effects of electric and magnetic fields on the LCMO channel resistance are discussed within the framework of phase separation scenario.
TL;DR: A dramatic and reversible change of the electronic structure is observed on crossing the Curie temperature, including charge localization on and spin-moment increase of Mn, together with Jahn-Teller distortions, both signatures of polaron formation.
Abstract: The temperature dependence of the electronic and atomic structure of the colossal magnetoresistive oxides La1� xSrxMnO3 (x � 0:3, 0.4) has been studied using core and valence level photoemission, x-ray absorption and emission, and extended x-ray absorption fine structure spectroscopy. A dramatic and reversible change of the electronic structure is observed on crossing the Curie temperature, including charge localization on and spin-moment increase of Mn, together with Jahn-Teller distortions, both signatures of polaron formation. Our data are also consistent with a phase-separation scenario.
TL;DR: The transverse resistivity in thin films of La 0.84Sr0.16MnO3 (LSMO) exhibits sharp field-symmetric jumps below TC.
Abstract: The transverse resistivity in thin films of La0.84Sr0.16MnO3 (LSMO) exhibits sharp field-symmetric jumps below TC. We show that a likely source of this behavior is the giant planar Hall effect combined with biaxial magnetic anisotropy. The effect is comparable in magnitude to that observed recently in the magnetic semiconductor Ga(Mn)As. It can be potentially used in applications such as magnetic sensors and nonvolatile memory devices.
TL;DR: In this article, the authors study current-driven magnetization switching in nanofabricated magnetic trilayers, and find an approximately linear dependence between magnetoresistance and inverse switching current.
Abstract: We study current-driven magnetization switching in nanofabricated magnetic trilayers, varying the magnetoresistance in three different ways. First, we insert a strongly spin-scattering layer between the magnetic trilayer and one of the electrodes, giving increased magnetoresistance. Second, we insert a spacer with a short spin-diffusion length between the magnetic layers, decreasing the magnetoresistance. Third, we vary the angle between layer magnetizations. In all cases, we find an approximately linear dependence between magnetoresistance and inverse switching current. We give a qualitative explanation for the observed behaviors, and suggest some ways in which the switching currents may be reduced.
Patent•
12 Jan 2004TL;DR: In this article, a method for forming a buffered-layer memory cell is described, which comprises: forming a bottom electrode, forming a colossal magnetoresistance (CMR) memory film overlying the bottom electrode; forming a memory-stable semiconductor buffer layer, typically a metal oxide, overlying memory film; and, forming top electrode overlying buffer layer.
Abstract: A method is provided for forming a buffered-layer memory cell. The method comprises: forming a bottom electrode; forming a colossal magnetoresistance (CMR) memory film overlying the bottom electrode; forming a memory-stable semiconductor buffer layer, typically a metal oxide, overlying the memory film; and, forming a top electrode overlying the semiconductor buffer layer. In some aspects of the method the semiconductor buffer layer is formed from YBa 2 Cu 3 O 7-X (YBCO), indium oxide (In 2 O 3 ), or ruthenium oxide (RuO 2 ), having a thickness in the range of 10 to 200 nanometers (nm). The top and bottom electrodes may be TiN/Ti, Pt/TiN/Ti, In/TiN/Ti, PtRhOx compounds, or PtIrOx compounds. The CMR memory film may be a Pr 1-X Ca X MnO 3 (PCMO) memory film, where x is in the region between 0.1 and 0.6, with a thickness in the range of 10 to 200 nm.
TL;DR: In this paper, the authors synthesized La0.67Ca0.33MnO3 (LCMO):xZnO composites through a citrate gel route and have characterized them for magnetic and magnetotransport properties.
Abstract: We have synthesized La0.67Ca0.33MnO3 (LCMO):xZnO () composites through a citrate gel route and have characterized them for magnetic and magnetotransport properties. In lower concentrations (), ZnO mostly goes into the perovskite lattice substituting Mn in LCMO and segregates less in the grain boundary region, but at higher concentration (x>0.13) it segregates mostly at the grain boundaries of LCMO and influences the transport properties significantly. A model is proposed which describes the overall resistivity of the system as a parallel combination of a low resistive intragrain conducting path and a high resistive intergrain insulating path. Using this approach, the grain and grain boundary contributions to the overall resistivity are separated for all the composites. The field dependent resistivity shows that all the composites have higher values of MR at the transition temperatures (TMI) compared to that in pure LCMO (x = 0). The highest value of MR is obtained for x = 0.10 and is 76.6% at 80 kOe field near TMI.
TL;DR: In this article, the electronic and magnetic properties of the colossal magneto resistance (CMR) compound Sr2FeMoO6 have been studied using different experimental techniques, namely X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS), and Xray absorption spectrometric (XAS).
Abstract: The electronic and magnetic properties of the colossal magneto resistance (CMR) compound Sr2FeMoO6 have been studied using different experimental techniques, namely X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). Furthermore, the magnetic properties have been studied in the temperature range of 4.2 K–800 K. The data confirm a highly ordered double perovskite crystal structure and is consistent with the tetragonal structure with 14/mmm symmetry. The Fe L edge has been probed by means of XAS, and comparison with results for a series of other iron oxides reveals a mixed valence state of Fe2+ and Fe3+. XPS of the Mo 3d and Fe 3s core levels confirms this point of view indicating a mixed valence state involving around 30% Fe3+–Mo5+ and 70% Fe2+–Mo6+ states, in good agreement with paramagnetic measurements which suggest 60% Fe2+ ions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, temperature-dependent magnetization, magnetoresistance and magneto-thermoelectric power of the K doped La 1− x Ca x − y K y MnO 3 type samples with x = 0.3 and 0⩽ y ⩽0.15 has been studied.
TL;DR: In this article, the authors reported results of integrated study of resistivity, magnetoresistance, Hall effect, thermopower, and magnetothermopower in single crystals with values of 0.15, 0.20, and 0.25 in the vicinity of the Curie temperature.
Abstract: We report results of integrated study of resistivity, magnetoresistance, Hall effect, thermopower, and magnetothermopower in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ single crystals with $x=0.15,0.20,0.25.$ The focus is on the vicinity of the Curie temperature. It is shown that near ${T}_{C}$ where the colossal magnetoresistance is observed the crystals are in insulator state. It is established that the conductivity in the manganites with different level of doping differs in nature. Near ${T}_{C},$ temperature and magnetic-field dependences of resistivity arise due to change of activation energy, which is linear in squared magnetization. The metal-insulator transition in the $x=0.20$ and 0.25 manganites occurs not at a certain temperature but in a temperature interval about 80 K wide.
TL;DR: In this paper, a qualitative explanation for the effect of disorder in the form of local random energies is presented, based on Monte Carlo simulations and the study of simplified toy models, calculating the density-of-states, cluster conductances using the Landauer formalism, and other observables.
Abstract: The physics of manganites appears to be dominated by phase competition among ferromagnetic metallic and charge-ordered antiferromagnetic insulating states. Previous investigations [Burgy et al., Phys. Rev. Lett. 87, 277202 (2001)] have shown that quenched disorder is important to smear the first-order transition between those competing states, and induce nanoscale inhomogeneities that produce the colossal magnetoresistance effect. Recent studies [Motome et al., Phys. Rev. Lett. 91, 167204 (2003)] have provided further evidence that disorder is crucial in the manganite context, unveiling an unexpected insulator-to-metal transition triggered by disorder in a one-orbital model with cooperative phonons. In this paper, a qualitative explanation for this effect is presented. It is argued that the transition occurs for disorder in the form of local random energies. Acting over an insulating states made out of a checkerboard arrangement of charge, with ``effective'' site energies positive and negative, this form of disorder can produce lattice sites with an effective energy near zero, favorable for the transport of charge. This explanation is based on Monte Carlo simulations and the study of simplified toy models, calculating the density-of-states, cluster conductances using the Landauer formalism, and other observables. A percolative picture emerges. The applicability of these ideas to real manganites is discussed.
01 Jan 2004
TL;DR: In this article, the authors proposed a new approach to the Defect Chemistry of Doped La1-DeltaMnO3+delta (Ln = La, Pr and M = Ni, Co) using the Laue method.
Abstract: Contributing Authors. Preface. Acknowledgements. Oxide Components for the Solid Oxide Fuel Cell J.B. Goodenough. Vacancy Segregation at Grain Boundaries in Ceramic Oxides N.D. Browning, et al. Metallic Conductivity and Magnetism: The Great Potential of Manganese and Cobalt Perovskites B. Raveau. Raman Diagnostics of LaCoO3 Based Properties N. Orlovskaya, D. Steinmetz. Mobility and Reactivity of the Surface and Lattice Oxygen of Some Complex Oxides with Perovskite Structure V.A. Sadykov, et al. LaFeO3 and LaCoO3 Based Perovskites: Preparation and Properties of Dense Oxygen Permeable Membranes K. Wiik, et al. Optimisation of Perovskite Materials for Fuel Electrodes S.W. Tao, J.T.S. Irvine. Single Crystal Growth of Oxides and Refractory Materials G. Balakrishnan, et al. Ionic Transport in Perovskite-Related Mixed Conductors: Ferrite-, Cobaltite-, Nickelate- and Gallate-Based Systems A. Kovalevsky, et al. Structural/Property Relationships of the Mixed Electronic/Ionic Conductors Based on Lanthanum Gallate N. Sammes. Microwave-Assisted Regeneration of Soot Filters Y. Zhang-Steenwinkel, et al. Microheterogeneous Solid Solutions in Perovskites: Formation, Microstructure and Catalytic Activity L.A. Isupova, et al. Phase Transitions and Ion Transport in SrFe1-xMx)2.5, Where M = Ga, Cr M.V. Patrakeev, et al. Connection of Giant Volume Magnetostriction with Colossal Magnetoresistance in Manganites L.I. Koroleva. SOFC Perspectives in Ukraine O.D. Vasylyev. Measurement of Oxygen Ionic Transport in Mixed Conductors E. Naumovich, et al. A New Approach to the Defect Chemistry of Doped La1-DeltaMnO3+delta K. Nakamura. Structure, Microstructure and Transport Properties of Mixed Conducting Lanthanum Gallate Based Perovskite Ceramics E.D. Politova, et al. Synthesis Structure Peculiarities of (La, Sr)MnO3 Based Nanomanganites I. Danilenko, et al. Nanoscale Magnetism and Magnetotransport Phenomena of (LaSr)MnO Compact V. Krivoruchko, et al. LSGM Single Crystals: Crystal Structure, Thermal Expansion, Phase Transitions and Conductivity L. Vasylechko, et al. Real Structure of LSGMO Crystal Studied by Laue Method D. Savytskii, et al. Microwave Regeneration of Diesel Soot Filters L.M. van der Zande, et al. Oxygen Transport in Composite Materials for Oxygen Separators and Syngas Membranes M. Dhallu, et al. Pulsed Lased Deposition of MIEC Sr4Fe6O13+-d Epitaxial Thin Films J.A. Pardo, et al. The Development of Gas Tight Thin Films of (La,Sr)(Ga,Fe)O3, (La,Sr)(Co,Fe)O3, and La2NiO4 for Oxygen Separation R. Muydinov, et al. Investigation into Thermal Expansion and Sintering of La2Mo4+d (Ln = La, Pr and M = Ni, Co) I.J.E. Brooks, et al. Oxide Ion Transport in Novel K2NiF4-Type Oxides C.N. Munnings, et al. Conductivity and Electronic Structure of Lanthanum Nickelites A.V. Zyrin, et al. Defect Chemistry of Mixed Ionic/Electronic P-Type Oxides H.U. Anderson, et al. Authors Index. Notes.
TL;DR: In this paper, the structural, magnetic and magneto-transport properties of La 0.7Sr0.3−xNaxMnO3 (0≤x≤0.2) manganites have been investigated.
TL;DR: In this article, the unusual geometrical properties of the Mn-O bonds network in CaMn 7 O 12 are discussed, and the thermal lattice expansion is anisotropic, with a local maximum around 50 K and a local minimum at 250 K.
Abstract: The crystal structure of CaMn 7 O 12 has been studied by high-resolution neutron and synchrotron radiation diffraction between 10 and 400 K . The unusual geometrical properties of the Mn–O bonds network in CaMn 7 O 12 are discussed. The thermal lattice expansion is anisotropic—the hexagonal lattice parameter c has a local maximum around 50 K and a local minimum at 250 K . The MnO 6 octahedra around Mn 3+ ions are apically Jahn-Teller distorted with two pairs of long ∼2.04,∼2.03 A and one short ∼1.89 A bonds without significant changes with temperature. There are weak peaks in the SR diffraction patterns which are due to a charge modulation, and which disappear above T CM =250 K . The maximum and minimum of the c -lattice parameter correlates with the magnetic phase transition at T C =49 K and the charge ordering transition T CM =250 K , respectively.
TL;DR: In this paper, the effect of grain size on structural, magnetic and transport properties in electron-doped manganites La 0.9Te 0.1MnO3 has been investigated.
TL;DR: In this paper, the phase separation signature of prototype manganites has been characterized by electron spin resonance (ESR) and the onset of the transitions has been determined from the temperature dependence of four main parameters deduced from the ESR spectra, the geff factor, the linewidth ΔHpp, the intensity and the line asymmetry.
TL;DR: In this article, the authors report results of the magnetotransport measurements on La0.67Ca0.33Mn1−xRuxO3 (0.1) compounds in the light of proposed magnetic phase separation in their previous work wherein two metal to insulator transitions (MITs) were reported.
TL;DR: Results strongly suggest that chemical disorder lowers the energy for polaron formation in manganese perovskites, and is the origin of the dramatic 50 K reduction in TC.
Abstract: Neutron studies of the effect of A-site chemical disorder on the ferromagnetic transition and spin dynamics for the magnetoresistive perovskite La0.54Ba0.46MnO3 are reported. The low temperature spin waves reveal that disorder reduces exchange interactions by only 9%. The development of a quasielastic peak in the spectrum below TC and long-time relaxation of the order parameter indicate that the transition is discontinuous in the disordered sample, while it appears continuous for the ordered sample. These results strongly suggest that chemical disorder lowers the energy for polaron formation in manganese perovskites, and is the origin of the dramatic 50 K reduction in TC.