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Title: Understanding the Insulating Phase in Colossal Magnetoresistance Manganites: Shortening of the Jahn-Teller Long-Bond across the Phase Diagram of La{sub 1-x}Ca{sub x}MnO{sub 3}

Abstract

The detailed evolution of the magnitude of the local Jahn-Teller (JT) distortion in La{sub 1-x}Ca{sub x}MnO{sub 3} is obtained across the phase diagram for 0{<=}x{<=}0.5 from high-quality neutron diffraction data using the atomic pair distribution function method. A local JT distortion is observed in the insulating phase for all Ca concentrations studied. However, in contrast with earlier local structure studies, its magnitude is not constant, but decreases continuously with increasing Ca content. This observation is at odds with a simple small-polaron picture for the insulating state.

Authors:
; ; ;  [1]; ;  [2];  [3];  [4];  [5]
  1. Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-2320 (United States)
  2. ISIS, CCLRC Rutherford Appleton Laboratory, Chilton-Didcot, OX11 0QX, Oxfordshire (United Kingdom)
  3. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
  4. Institute Laue-Langevin, Boite Postale 156, 38042 Grenoble Cedex 9 (France)
  5. Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
Publication Date:
OSTI Identifier:
20951196
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 13; Other Information: DOI: 10.1103/PhysRevLett.98.137203; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CALCIUM COMPOUNDS; DISTRIBUTION FUNCTIONS; JAHN-TELLER EFFECT; LANTHANUM COMPOUNDS; MAGNETORESISTANCE; MANGANATES; NEUTRON DIFFRACTION; PHASE DIAGRAMS

Citation Formats

Bozin, E. S., De Coninck, A. J., Paglia, G., Billinge, S. J. L., Schmidt, M., Radaelli, P. G., Mitchell, J. F., Chatterji, T., and Proffen, Th. Understanding the Insulating Phase in Colossal Magnetoresistance Manganites: Shortening of the Jahn-Teller Long-Bond across the Phase Diagram of La{sub 1-x}Ca{sub x}MnO{sub 3}. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.137203.
Bozin, E. S., De Coninck, A. J., Paglia, G., Billinge, S. J. L., Schmidt, M., Radaelli, P. G., Mitchell, J. F., Chatterji, T., & Proffen, Th. Understanding the Insulating Phase in Colossal Magnetoresistance Manganites: Shortening of the Jahn-Teller Long-Bond across the Phase Diagram of La{sub 1-x}Ca{sub x}MnO{sub 3}. United States. doi:10.1103/PHYSREVLETT.98.137203.
Bozin, E. S., De Coninck, A. J., Paglia, G., Billinge, S. J. L., Schmidt, M., Radaelli, P. G., Mitchell, J. F., Chatterji, T., and Proffen, Th. Fri . "Understanding the Insulating Phase in Colossal Magnetoresistance Manganites: Shortening of the Jahn-Teller Long-Bond across the Phase Diagram of La{sub 1-x}Ca{sub x}MnO{sub 3}". United States. doi:10.1103/PHYSREVLETT.98.137203.
@article{osti_20951196,
title = {Understanding the Insulating Phase in Colossal Magnetoresistance Manganites: Shortening of the Jahn-Teller Long-Bond across the Phase Diagram of La{sub 1-x}Ca{sub x}MnO{sub 3}},
author = {Bozin, E. S. and De Coninck, A. J. and Paglia, G. and Billinge, S. J. L. and Schmidt, M. and Radaelli, P. G. and Mitchell, J. F. and Chatterji, T. and Proffen, Th.},
abstractNote = {The detailed evolution of the magnitude of the local Jahn-Teller (JT) distortion in La{sub 1-x}Ca{sub x}MnO{sub 3} is obtained across the phase diagram for 0{<=}x{<=}0.5 from high-quality neutron diffraction data using the atomic pair distribution function method. A local JT distortion is observed in the insulating phase for all Ca concentrations studied. However, in contrast with earlier local structure studies, its magnitude is not constant, but decreases continuously with increasing Ca content. This observation is at odds with a simple small-polaron picture for the insulating state.},
doi = {10.1103/PHYSREVLETT.98.137203},
journal = {Physical Review Letters},
number = 13,
volume = 98,
place = {United States},
year = {Fri Mar 30 00:00:00 EDT 2007},
month = {Fri Mar 30 00:00:00 EDT 2007}
}
  • 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
  • This work presents a study of how the magnetic and temperature variables, as well as the measurement rate, affect magnetic and structural phase transitions for La{sub 0.7}Ca{sub 0.3−x}Sr{sub x}MnO{sub 3} (x=0.15, 0.08, 0.07 and 0.06) manganites. A single phase rhombohedral crystal structure for Sr{sub 0.15} compound and a single phase orthorhombic crystal structure for Sr{sub 0.08}, Sr{sub 0.07}, and Sr{sub 0.06} compounds were identified by X ray diffraction. The Curie temperature adjustment to room temperature was reached for Sr{sub 0.07} sample, in which a Jahn-Teller transition was observed. This Jahn-Teller transition showed a susceptible response to 0.5, 1, 2, 3,more » 5 and 7 K/min measurement rates, and was revealed without measurement sequence at 234, 257, 196, 233, 245 and 238 K respectively in thermomagnetic curves (10 mT). Also, Curie temperature increases sequentially around 2 K for the same measurement rates. To avoid magnetic field effect, a differential scanning calorimetry for Sr{sub 0.07} sample was obtained in the same temperature region, for 2, 3, 5, 7 K/min showing the Jahn-Teller phase transition at 225 K and a vibrational like behavior in the heat flux below 225 K, for all the temperature rates. The latter, is related to the static to dynamic Jahn-Teller transition. Furthermore, Curie temperature appears around 284 K.« less
  • We report Mn K-edge x-ray absorption near edge structure (XANES) calculations of the La{sub 1-x}Ca{sub x}MnO{sub 3} manganites considering three pair correlations, according to the three fundamental degrees of freedom governing their unusual electronic properties, namely, the electronic structure of the unoccupied states probed by the Mn K-edge profile versus (i) local atomic distortions; (ii) local magnetic ordering; and (iii) the charge-transfer nature of the Mn-O bonds. The calculations are accompanied by Mn K-edge XANES measurements in the temperature range 30--300 K. The main features of the absorption edge can be qualitatively reproduced in terms of single-electron multiple-scattering calculations formore » an 87-atom cluster. Lattice polaronic distortions in La{sub 0.7}Ca{sub 0.3}MnO{sub 3} are simulated assuming a strongly distorted orthorhombic structure above and an almost undistorted rhombohedral structure below T{sub c}. The results roughly reproduce the energy ''shift'' across T{sub c} observed experimentally. Mn K-edge spin-polarized XANES spectra of the x=0, 0.3, and 1 samples are presented. An energy splitting between the majority- and minority-spin spectra of 0.5--1.1 eV contributes to the total XANES broadening below the Neel (Curie) temperature. A small feature B{sub 3} standing approximately 6 eV above the main absorption peak is beyond the scope of single-electron calculations; it is assigned to a shake-up transition. To illustrate, the calculated Mn K edge is obtained as the convolution product of the single-electron XANES and the spectrum of many-body excitations in the Mn-O electronic states upon the sudden switching on of the Mn 1s core hole. We investigate the charge-transfer (CT) versus. Mott-Hubbard-type ground state using the U{sub d}, {Delta}, and the T{sub dp} parameters determined by previous Mn 2p x-ray photoemission spectroscopy measurements and find that LaMnO{sub 3} should be viewed as a CT-type insulator with a substantial O 2p component in the ground state. In light of these results the controversial issue of Mn valence states in the manganites is critically reexamined. We argue that the disproportionation may be understood as a mixture of the CT many-body electronic configurations coupled with spin and lattice degrees of freedom.« less
  • Evolution of the average and local crystal structure of Ca-doped LaMnO 3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO 6 octahedra across the OR transition at T S~720 K.more » The study utilized explicit two-phase PDF structural modeling, revealing that away from T MI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO 3. The results hence do not support the percolative scenario for the MI transition in La 1–xCa xMnO 3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO 3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.« less
  • Evolution of the average and local crystal structure of Ca-doped LaMnO 3 has been studied across the metal to insulator (MI) and the orthorhombic to rhombohedral (OR) structural phase transitions over a broad temperature range for two Ca concentrations (x = 0.18,0.22). Combined Rietveld and high real space resolution atomic pair distribution function (PDF) analysis of neutron total scattering data was carried out with aims of exploring the possibility of nanoscale phase separation (PS) in relation to MI transition, and charting the evolution of local Jahn-Teller (JT) distortion of MnO 6 octahedra across the OR transition at T S~720 K.more » The study utilized explicit two-phase PDF structural modeling, revealing that away from T MI there is no evidence for nanoscale phase coexistence. The local JT distortions disappear abruptly upon crossing into the metallic regime both with doping and temperature, with only a small temperature-independent signature of quenched disorder being observable at low temperature as compared to CaMnO 3. The results hence do not support the percolative scenario for the MI transition in La 1–xCa xMnO 3 based on PS, and question its ubiquity in the manganites. In contrast to LaMnO 3 that exhibits long-range orbital correlations and sizable octahedral distortions at low temperature, the doped samples with compositions straddling the MI boundary exhibit correlations (in the insulating regime) limited to only ~1 nm with observably smaller distortions. In the x = 0.22 sample local JT distortions are found to persist across the OR transition and deep into the R phase (up to ~1050 K), where they are crystallographically prohibited. As a result, their magnitude and subnanometer spatial extent remain unchanged.« less