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Title: Fragility of the A-Type AF and CE Phases of Manganites: Insulator-To-Metal Transition Induced by Quenched Disorder

Abstract

Using Monte Carlo simulations and the two eg-orbital model for manganites, the stability of the CE and A-type antiferromagnetic insulating states is analyzed when quenched disorder in the superexchange JAF between the t2g localized spins and in the on-site energies is introduced. At vanishing or small values of the electron-Jahn-Teller phonon coupling, the previously hinted "fragility" of these insulating states is studied in detail, focusing on their charge transport properties. This fragility is here found to induce a rapid transition from the insulator to a poor metallic state upon the introduction of disorder. A possible qualitative explanation is presented based on the close proximity in energy of ferromagnetic metallic phases, and also on percolative ideas valid at large disorder strength. The scenario is compared with previously discussed insulator-to-metal transitions in other contexts. This particularly severe effect of disorder must be present in other materials as well, in cases involving phases that arise as a compromise between very different tendencies, as it probably occurs with striped states in the cuprates.

Authors:
 [1];  [1];  [2];  [1]
  1. ORNL
  2. Florida State University
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC)
OSTI Identifier:
930842
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 73
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CHARGE TRANSPORT; CUPRATES; FOCUSING; PHONONS; STABILITY; AF; CE Fragility

Citation Formats

Alvarez, Gonzalo, Aliaga, Horacio A, Sen, Cengiz, and Dagotto, Elbio R. Fragility of the A-Type AF and CE Phases of Manganites: Insulator-To-Metal Transition Induced by Quenched Disorder. United States: N. p., 2006. Web. doi:10.1103/PhysRevB.73.224426.
Alvarez, Gonzalo, Aliaga, Horacio A, Sen, Cengiz, & Dagotto, Elbio R. Fragility of the A-Type AF and CE Phases of Manganites: Insulator-To-Metal Transition Induced by Quenched Disorder. United States. doi:10.1103/PhysRevB.73.224426.
Alvarez, Gonzalo, Aliaga, Horacio A, Sen, Cengiz, and Dagotto, Elbio R. Sun . "Fragility of the A-Type AF and CE Phases of Manganites: Insulator-To-Metal Transition Induced by Quenched Disorder". United States. doi:10.1103/PhysRevB.73.224426.
@article{osti_930842,
title = {Fragility of the A-Type AF and CE Phases of Manganites: Insulator-To-Metal Transition Induced by Quenched Disorder},
author = {Alvarez, Gonzalo and Aliaga, Horacio A and Sen, Cengiz and Dagotto, Elbio R},
abstractNote = {Using Monte Carlo simulations and the two eg-orbital model for manganites, the stability of the CE and A-type antiferromagnetic insulating states is analyzed when quenched disorder in the superexchange JAF between the t2g localized spins and in the on-site energies is introduced. At vanishing or small values of the electron-Jahn-Teller phonon coupling, the previously hinted "fragility" of these insulating states is studied in detail, focusing on their charge transport properties. This fragility is here found to induce a rapid transition from the insulator to a poor metallic state upon the introduction of disorder. A possible qualitative explanation is presented based on the close proximity in energy of ferromagnetic metallic phases, and also on percolative ideas valid at large disorder strength. The scenario is compared with previously discussed insulator-to-metal transitions in other contexts. This particularly severe effect of disorder must be present in other materials as well, in cases involving phases that arise as a compromise between very different tendencies, as it probably occurs with striped states in the cuprates.},
doi = {10.1103/PhysRevB.73.224426},
journal = {Physical Review B},
number = ,
volume = 73,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Using Monte Carlo simulations and the twomore » $$e_{\rm g}$$-orbital model for manganites, the stability of the CE and A-type antiferromagnetic insulating states is analyzed when quenched disorder in the superexchange $$J_{\rm AF}$$ between the $$t_{\rm 2g}$$ localized spins and in the on-site energies is introduced. At vanishing or small values of the electron-(Jahn-Teller)phonon coupling, the previously hinted ''fragility'' of these insulating states is studied in detail, focusing on their charge transport properties. This fragility is here found to induce a rapid transition from the insulator to a (poor) metallic state upon the introduction of disorder. A possible qualitative explanation is presented based on the close proximity in energy of ferromagnetic metallic phases, and also on percolative ideas valid at large disorder strength. The scenario is compared with previously discussed insulator-to-metal transitions in other contexts. It is argued that the effect unveiled here has unique properties that may define a new class of giant effects in complex oxides. This particularly severe effect of disorder must be present in other materials as well, in cases involving phases that arise as a compromise between very different tendencies, as it occurs with striped states in the cuprates.« less
  • The study of the manganites Ln{sub 0.5}Ca{sub 0.5}Mn{sub 1{minus}x}Ni{sub x}O{sub 3} (Ln = Pr, Nd, Sm) shows that the introduction of nickel on the Mn site provokes the disappearance of charge ordering (CO). But most important, it is demonstrated for the first time that doping with nickel induces a metal-insulator transition for Ln = Pr or Nd, in spite of the small size of the interpolated cations. All the compounds of these series exhibit colossal magnetoresistance (CMR) properties with resistance ratios (RR) ranging from 5.10{sup 3} at 75 K to 10{sup 8} at 60 K under 7 T, whereas themore » undoped phases either are not magnetoresistant (Ln = Pr, Sm) or exhibit much smaller RR (20 at 100 K for Ln = Nd). The magnetotransport properties of these Ni-doped manganites are compared to those of Cr- and Co-doped phases and their evolution is discussed, taking into consideration two antagonist factors: the average size of the interpolated cations and the size mismatch between Ln{sup 3+} and Ca{sup 2+}.« less
  • In this work, the influence of disorder on the electrical properties (DC conductivity and Magnetoresistance) of amorphous conducting carbon films, prepared by the pyrolysis of Tetra chloro phthalic anhydride, is reported and discussed. The low temperature electrical properties are analyzed in terms of the various models developed for disordered electronic systems. The results indicate the possibility of a metal--insulator (M-I) transition, both as a function of preparation temperature and an external magnetic field.
  • The insulator-to-metal transition in the manganite La{sub 0.52}Y{sub 0.15}Ca{sub 0.33}MnO{sub 3} (T{sub IM}{approx}115 K) has been studied by high-resolution neutron powder diffraction. The cell volume contraction at the Curie point is accompanied by a remarkable decrease of the Jahn-Teller distortion in MnO{sub 6} octahedra. The change of the Mn-O bond lengths at T{sub IM} is anisotropic and brings about a drop out of the basal-plane collective distortion mode Q{sub 2}, proposed to be the deformation responsible for the band split of e{sub g{up_arrow}} orbitals. This is consistent with the double-exchange picture, and precludes simple ferromagnetic exchange. {copyright} {ital 1997} {italmore » The American Physical Society}« less
  • Lattice effects on the anisotropic magnetic and transport properties have been investigated for single crystals of (La{sub 1{minus}z}Nd{sub z}){sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} with a layered structure. The ferromagnetic transition temperature T{sub C} is suppressed from T{sub C}=130 K for z=0.0 to 80 K for z=0.2, and eventually the transition disappears beyond z=0.4. From the significant change of the magnetic anisotropy, we have found that the suppression originates from the increasing d{sub 3z{sup 2}{minus}r{sup 2}} character in the occupied e{sub g} state due to the Jahn-Teller distortion of the MnO{sub 6} octahedra. Our observations indicate that the effects of chemicalmore » substitution are qualitatively different between the cubic and layered doped manganites. {copyright} {ital 1997} {ital The American Physical Society}« less