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Electronically smectic-like phase in a nearly half-doped manganite

Electronically smectic-like phase in a nearly half-doped manganite. J. A. Fernandez-Baca Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. INTERNATIONAL WORKSHOP ON SELF-ORGANIZED STRONGLY CORRELATED ELECTRON SYSTEMS Seillac, France May 29-31, 2006. Collaborators. F. Ye ( ORNL )

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Electronically smectic-like phase in a nearly half-doped manganite

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  1. Electronically smectic-like phase in a nearly half-doped manganite J. A. Fernandez-Baca Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA INTERNATIONAL WORKSHOP ON SELF-ORGANIZED STRONGLY CORRELATED ELECTRON SYSTEMS Seillac, France May 29-31, 2006

  2. Collaborators • F. Ye (ORNL) • P. Dai (Univ. of Tennessee, ORNL) • J. W. Lynn (NIST) • H. Kawano-Furukawa (Ochanomizu University, Japan) • H. Yoshizawa (ISSP-University of Tokyo, Japan) • Y. Tomioka (CERC, Japan) • Y. Tokura (U. of Tokyo, CERC, Japan

  3. Outline • Motivation:Charge and orbital ordering in the CMR manganites are associated with the insulating state in the manganite perovskites. • “CE-type” CO/OO and AF ordering is prevalent and not so far energetically from the metal state • Need to better understand CE-type CO/OO and AF order • Neutron studies in Pr1-x(Ca1-ySry)xMnO3 near x=0.5 Evidence of weakly coupled 1D spin chains (smetic-like) above TN • Discussion Ye et al Phys. Rev. B 72, 212404 (2005)

  4. CMR perovskite manganites:Substitution of Ln3+ for Ca2+ results in mixed valence Mn • Ln1-xAxMnO3: perovskite structure • Ln3+=Lanthanide (La,Pr,Nd…) • A2+=Ca,Sr,Ba… • Mn:B site A site

  5. Rich phase diagram: Metallic state is associated with ferromagnetism due to Double exchange Insulator-Metal transition coupled with the Paramagnetic-Ferromagnetic (PM-FM) transition P. Schiffer et al, PRL (1995)

  6. Rich phase diagram: Insulating state is associated with Charge/orbital Ordering (CO-OO) Pr0.5Sr0.5MnO3 50% Mn3+with50% Mn4+ CE-type CO-OO Tomioka et al, PRL 74 CO-OO promotes AF and insulating behavior

  7. Rich phase diagram: Insulating state is associated with Charge/orbital Ordering (CO-OO) 50% Mn3+with50% Mn4+ CE-type CO-OO The prevalent CO-OO and AF order is of the so-called CE-type originally proposed by Goodenough (Phys. Rev. 1955) Tomioka et al, PRL 74 CO-OO promotes AF and insulating behavior

  8. Neutron scattering of CE-type CO-OO CO-OO peak at [1/4,1/4]

  9. Charge/orbital ordering CO-OO can be melted by an external magnetic field Pr 1-x(Ca1-ySry)xMnO3 y=0.20, x=0.45 Tomioka and Tokura PRB 66, 104416 (2002) Ye et al (unpublished)

  10. Short range CO/OO fluctuations in LCMO30 above TC CO-OO peak at [1/4,1/4] CMR seems to result from the competition of the tendency to CE CO/OO and DE Dai et al., PRL (2000)

  11. Trying to understand the CE-type CO-OO • Goodenough (1955) • charge ordering at high temperature ( ~ covalent bond energy) • magnetic ordering at much lower temperature (exchange interaction). • van den Brink et al. PRL (1999) • Anisotropy of short range DE • Competition between Kinetic Energy Magnetic Exchange Energy • Orbital degeneracy

  12. Trying to understand the CE-typeCO-OO Zener polarons (Daoud-Aladine) Trapping of electrons in Mn pairs (Zener polarons) • Mn3+/Mn4+ picture challenged • Resonant x-ray experiments suggets magnetic moments at Mn3+ and Mn4+ not so different • Magnetic powder diffraction, small difference in the magnetic moments • Popović et al., PRL (2002) • Jahn-Teller Distortion • Onsite Coulomb repulsion • Mn3+/Mn4+ picture ???

  13. Trying to understand the CE-typeCO-OO • Important questions • Origin of CE-type structure • Role of magnetism • What about Mn3+ and Mn4+, are they really different? (in magnitude, in character) • Are there really zigzag chains of Mn moments?

  14. Case study: CO-OO Pr0.55(Ca1-ySry)0.45MnO3(PCSMO45) (Pr,Ca)MnO3 (Pr,Sr)MnO3 Tomioka et al. (2002)

  15. Magnetic form factor CE type structure in real and reciprocal space

  16. Charge/Orbital Ordering of PCSMO45 (Synchrotron X-ray) CO-OO peak at large equivalent [1/4,1/4] T=240K T=160K T=130K

  17. Resistivity, CO-OO and AF Ordering in PCSMO45

  18. Anisotropic AFM fluctuation in PCSMO45 • Highly anisotropic • Suggest low-dimensional behavior (1D, smectic)

  19. Mn3+ Mn4+ Comparison of Mn3+ and Mn4+ in PCSMO45 Scattering from Mn3+ and Mn4+ have distinct orbital character F. Ye, et al., PRB (2005)

  20. Comparison of AFM (Mn3+ and Mn4+) in PCSMO45 • AFM from Mn3+ shows strong hysteresis • AFM from Mn4+ nearly no hysteresis

  21. Evolution of CE-type CO-OO and magnetic ordering TN < T < TCO T< TN First observation of quasi long-range 1D spin chains

  22. Discussion • Quasi long range 1D zigzag spin changes are the “building blocks” of the CE-structure • Consistent with the new “soft phase” proposed by Milward et al (Nature 2005), Dagotto et al (Science, 2005)

  23. General feature in “strongly correlated electron” system S. A. Kivelson, Nature (1998) charge/spin order in cuprates (Stripes) Tranquada, Nature (2004)

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