Neutron-diffraction study of the Jahn-Teller transition in stoichiometric<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">LaMnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Rodrı́guez-Carvajal, J.; Hennion, M.; Moussa, F.; Moudden, A. H.; Pinsard, L.; Revcolevschi, A.

doi:10.1103/physrevb.57.r3189

Cited by 691 publications

(531 citation statements)

References 27 publications

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“…7͒, and is thus somewhat smaller than the angle JT = 108°deduced from the lattice distortions in LaMnO 3 . 68,69 This can be seen as a compromise between the orbital interactions involving the lattice and the purely electronic superexchange orbital interactions, so it is reasonable to expect that Ͻ JT .…”

Section: Magnetic Interactions In Lamnomentioning

confidence: 99%

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

et al. 2005

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The temperature dependence and anisotropy of optical spectral weights associated with different multiplet transitions is determined by the spin and orbital correlations. To provide a systematic basis to exploit this close relationship between magnetism and optical spectra, we present and analyze the spin-orbital superexchange models for a series of representative orbital-degenerate transition metal oxides with different multiplet structure. For each case we derive the magnetic exchange constants, which determine the spin wave dispersions, as well as the partial optical sum rules. The magnetic and optical properties of early transition metal oxides with degenerate t 2g orbitals ͑titanates and vanadates with perovskite structure͒ are shown to depend only on two parameters, viz. the superexchange energy J and the ratio of Hund's exchange to the intraorbital Coulomb interaction, and on the actual orbital state. In e g systems important corrections follow from charge transfer excitations, and we show that KCuF 3 can be classified as a charge transfer insulator, while LaMnO 3 is a Mott insulator with moderate charge transfer contributions. In some cases orbital fluctuations are quenched and decoupling of spin and orbital degrees of freedom with static orbital order gives satisfactory results for the optical weights. On the example of cubic vanadates we describe a case where the full quantum spin-orbital physics must be considered. Thus information on optical excitations, their energies, temperature dependence, and anisotropy, combined with the results of magnetic neutron scattering experiments, provides an important consistency test of the spin-orbital models, and indicates whether orbital and/or spin fluctuations are important in a given compound. I. SUPEREXCHANGE AND OPTICAL EXCITATIONS AT ORBITAL DEGENERACYThe physical properties of Mott ͑or charge transfer͒ insulators are dominated by large on-site Coulomb interactions ϰU which suppress charge fluctuations. Quite generally, the Coulomb interactions lead then to strong electron correlations which frequently involve orbitally degenerate states, such as 3d ͑or 4d͒ states in transition metal compounds, and are responsible for quite complex behavior with often puzzling transport and magnetic properties. 1 The theoretical understanding of this class of compounds, with the colossal magnetoresistance ͑CMR͒ manganites as a prominent example, 2,3 has substantially advanced over the last decade, 4 after it became clear that orbital degrees of freedom play a crucial role in these materials and have to be treated on equal footing with the electron spins, which has led to a rapidly developing field, orbital physics. 5 Due to the strong onsite Coulomb repulsion, charge fluctuations in the undoped parent compounds are almost entirely suppressed, and an adequate description of these strongly correlated insulators appears possible in terms of superexchange. 6 At orbital degeneracy the superexchange interactions have a rather rich structure, represented by the so-called spin-orbita...

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Section: Magnetic Interactions In Lamnomentioning

confidence: 99%

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

et al. 2005

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“…The data assigned to a monoclinic space group by Mitchell et al 9 can be well refined in the orthorhombic space group as well with fewer degrees of freedom. 11 An excellent summary of the situation is presented in Rodriguez-Carvajal et al 11 In this structure the long d 3z 2 −r 2 orbitals lie in the same (basal) plane in a checkerboard type of arrangement so the bonds are long-short-long-short as you move from Mn to Mn along the Mn-O-Mn bond. Since all the long bonds lie in this plane, the separation of the Mn ions in the perpendicular direction (c-axis in the P bnm setting and b axis in the P nma setting) is shorter.…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4][5][6][7][8][9][10][11] Differences between these studies occur largely because of the sensitivity of the structure to the sample stoichiometry which depends on synthesis conditions. 9 It appears fairly widely accepted now that the correct structure for stoichiometric LaMnO 3 at low temperature is orthorhombic (space group P bnm or P nma depending on convention).…”

Section: Introductionmentioning

confidence: 99%

Measurement of the local Jahn-Teller distortion inLaMnO3.006

et al. 1999

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The atomic pair distribution function (PDF) of stoichiometric LaMnO3 has been measured. This has been fit with a structural model to extract the local Jahn-Teller distortion for an ideal Mn 3+ O6 octahedron. These results are compared to Rietveld refinements of the same data which give the average structure. Since the local structure is being measured in the PDF there is no assumption of long-range orbital order and the real, local, Jahn-Teller distortion is measured directly. We find good agreement both with published crystallographic results and our own Rietveld refinements suggesting that in an accurately stoichiometric material there is long range orbital order as expected. The local Jahn-Teller distortion has 2 short, 2 medium and 2 long bonds. This implies that there is some mixing of the d 3z 2 −r 2 and d x 2 −y 2 states and the occupied state is not pure d 3z 2 −r 2 symmetry. The Debye temperature of the Mn and O ions has also been calculated as ΘD(Mn)= 1000 ± 100 K, ΘD(O apical )= 980 ± 30 K and ΘD(O basal ) = 601 ± 8 K.

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“…Structural parameters for the low-temperature orthorhombic Pbnm phase of LMO have been taken from the experimental neutron diffraction study. 21 The experimentally defined geometries have been used in our first-principles calculations, because magnetic properties, especially the coupling constants J, are strongly affected by the choice of crystal structure. At the same time, we note that lattice parameters and atomic coordinates of both LMO and LSM optimized by means of the B3LYP hybrid technique are very close to the experimentally observed ones.…”

mentioning

confidence: 99%

“…19 In order to verify our approach, we also performed a number of test calculations on LMO in its low-temperature orthorhombic structure, which is the parent compound for LSM and well studied by various experiments and calculations. 12,13,[20][21][22] To model LSM at low doping ͑x =1/8͒ in the lowtemperature regime ͑orthorhombic Pbnm phase͒, we used structural parameters derived experimentally by means of neutron diffraction. 23 This orthorhombic structure of ABO 3 perovskite comprises four formula units.…”

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confidence: 99%

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

et al. 2007

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We present the results of ab initio calculations on magnetic and electronic structures of La 1−x Sr x MnO 3 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 La 0.875 Sr 0.125 MnO 3 in both the low-temperature orthorhombic and the high-temperature pseudocubic phases. This is in contrast to its parent compound LaMnO 3 , 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. Sr-doped LaMnO 3 ͑La 1−x Sr x MnO 3 , LSM͒ is one of many extensively studied perovskite-type oxides, attractive due to its colossal magnetoresistivity, a spin-glass behavior, a metal-to-insulator transition ͓at ϳ360 K for x = 0.3 ͑Ref. 1͔͒, charge ordering after doping with Sr, and a ferromagneticantiferromagnetic transitions observed. One of its important applications is also the use as a promising cathode material in high-temperature solid oxide fuel cells ͑SOFCs͒. 2 The high operating temperature of current SOFC technology is mandated by the necessity of high oxygen molecule reduction rate at the fuel cell cathode and high oxygen ion mobility in the solid electrolyte and in the cathode bulk or on surfaces and grain boundaries. Technologically, the first requirement ͑and partially the second one͒ can be met by reducing the thickness of electrolyte and cathode layers, as it is implemented in the Jülich planar substrate SOFC concept, where thin electrolyte ͑yttria stabilized zirconium oxide͒ and cathode layers ͑LSM or ͕Co, Fe͖-doped LaMnO 3 ͒ are supported by a millimeter thick nickel cermet anode. 3 Elucidating the mechanisms of oxygen reduction and mobility on LSM surfaces and in the bulk of LSM is thus beneficial for understanding the limitations of the currently used materials in SOFC technology and secondly aiding the development of higher-performance materials. LSM compounds exhibit a large variety of properties depending on the La/ Sr ratio, the degree of oxygen nonstoichiometry, temperature and/or pressure conditions, sample preparation, etc. Even at high SOFC working temperatures ͑T Ͼ 780 K͒, when cooperative Jahn-Teller distortion disappears, magnetic orbital ordering still can take place. Knowledge of proper spin redistribution in manganites is especially important because of the four unpaired electrons on Mn, which demand open-shell calculations. Thus, before one starts modeling the complex surface processes, it is indispensable to first investigate the magnetic and electronic structure of bulk LSM. In the current study, we chose to investigate the LSM with a 12.5% Sr doping, which is somewhat larger than typical experimental concentrations ͑ഛ10% Sr͒ in order to simplify the calculations ͑the larger the Sr content, the smaller the necessary system size͒.Recent series of local spin-density approximatio...

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Neutron-diffraction study of the Jahn-Teller transition in stoichiometricLaMnO3

Cited by 691 publications

References 27 publications

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

Measurement of the local Jahn-Teller distortion inLaMnO3.006

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

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