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Synchrotron and Neutron Studies of Ordering Phenomena on Perovskite and Spinel Lattices

This paper discusses the use of synchrotron and neutron studies to explore ordering phenomena on perovskite and spinel lattices. The focus is on charge, orbital, and magnetic ordering in various materials, including manganites and ferrites. The significance of powder diffraction in studying high-temperature phases is emphasized.

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Synchrotron and Neutron Studies of Ordering Phenomena on Perovskite and Spinel Lattices

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  1. Ordering phenomena on the perovskite and spinel lattices: synchrotron and neutron studiesPaolo G. RadaelliISIS Facility, Rutherford Appleton Laboratory and Dept of Physics & Astronomy, University College London

  2. Powder diffraction in the 21st century? • In many systems single crystal diffraction is the tool of choice to study ordering phenomena. There are many classic and recent examples, esp. in low-dimensional systems. [1] J. L. de Boer, A. Meetsma, J. Baas, and T. T. M. Palstra, PRL 84 (2000) 3962. NaV2O5 [1] • Yet, powder diffraction still gives a significant contribution, esp. in systems where the high-temperature phase is highly symmetric, (perovskites, spinels, pyrochlores, etc.) Paolo G. Radaelli, Oxford, Sept 2003

  3. Outline • Charge ordering in manganites: methodology. • Frustrated systems. • Fe3O4 revisited. • Dimer formation on the pyrochlore lattice: • ½-filled system: CuIr2S4 • 1-filled system: MgTi2O4 • Data quality issues. • Summary. Paolo G. Radaelli, Oxford, Sept 2003

  4. Mn+3 Mn+3 Mn+4 Mn+3 Mn+3 Mn+4 Mn+3 Mn+3 Charge and Orbital Ordering in La0.5Ca0.5 MnO3 1E.O. Wollan and W.C. Koehler, Phys. Rev. 100 (1), 545-563 (1955).

  5. NPD: average structure

  6. û û c û û û û û û û û û û a Special position: 4b [ ] 0,0, ½ Charge Ordering: symmetry analysis Pnma (Pbnm) y=0 y= ½

  7. Special position: 4b [ ] 0,0, ½ Charge Ordering: symmetry analysis P21/m c a y=0 y= ½

  8. û û û û û û Orbital Ordering: symmetry analysis P21/m (2a) c a

  9. Charge and Orbital Ordering in La0.5Ca0.5 MnO3 Mn+3 Mn+3 Mn+4 Mn+3 Mn+3 Mn+4 Mn+3 Mn+3 PGR et al., PRB

  10. SX results A. Daoud-Aladine et al., PRL 89 (2002) 097205

  11. “Wigner crystal” model “Stripe” model c axis a) b) a axis frustrated spin up Mn+3 FM spin down Mn+4 AFM La0.333Ca0.667MnO3Charge, Orbital and Magnetic Ordering

  12. Neutron Powder Diffraction Data

  13. c axis a axis La0.333Ca0.667MnO3Canted Magnetic Structure

  14. “Wigner crystal” model “Stripe” model 0.60 0.20 0.10 0.40 0.00 0.20 -0.10 0.00 -0.20 -0.20 -0.30 -0.40 -0.40 -0.60 -0.50 -3w -2w -w 0 w 2w 3w -3w -2w -w 0 w 2w 3w Frequency Frequency Displacement Patterns for the“Wigner crystal” and “Stripe” models a) b)

  15. Comparison with x-ray data a) Average structureb) “Stripe” modelc) “Wigner Crystal” model

  16. La0.333Ca0.667MnO3Superstructure Neutron Powder Diffraction Data

  17. Magnetic structure NPD Symmetry and mode analysis A priori knowledge Mode screening SXPD Full structural refinement NPD, SXPD Charge and Orbital Ordering : Flow Chart ADP magnitude/direction NPD Propagation vectors SXPD, ED Neutrons X-rays/el. Theory N&X

  18. Bernal-Fowler (Pauling) rules

  19. The Anderson Condition Anderson, P. W. Ordering and Antiferromagnetism in Ferrites. Physical Review102, 1008-1013 (1956). U=2e2/d Charge U=2J Magnetic E=2nTU E=6U E=3U

  20. In 1939, Verwey discovered a sharp increase of the resistivity of Fe3O4 around 120K, accompanied by a structural distortion1. • He then proposed to write the chemical formula of magnetite as Fe3+Fe2.5+2O4, all the tetrahedral Fe being 3+. At the M-I transition, charges on the B-site would order onto an orthorhombic superstructure. 1E.J.W. Verwey, Nature 144 (1939) pp. 327-328. 2E.J.W. Verwey and P.W. Haayman, Physica 9 (1941) pp. 979-987 The Verwey transition

  21. -1 +1 -1 +1 -1 +1 -1 +1 -1 The Verwey Model Z=2 Z=1 Z=0

  22. Neutron data (HRPD) Synchrotron data (BM16) J.P. Wright, J.P. Attfield and P.G. Radaelli, PRL 87 (2001) 266401 J.P. Wright, J.P. Attfield and P.G. Radaelli, PRB 66 (2002) 214422

  23. - - - - - - - - + + + + + + + + - - - - 2 2 2 3 4 3 1 1 1 3 4 3 2 2 2 4 3 4 1 1 1 4 3 4 2 2 2 B1 (2.4+) B2 (2.6+) B3 (2.6+) B4 (2.4+)

  24. “Bond” ordering on a pyrochlore lattice • Conventional charge ordering concept may fail in many systems (Fe3O4, Manganites, etc.). One never recovers integral valences. • Possibility of Peiers and spin-Peierls-like transition on the pyrochore lattice (spinels, pyrocholres, etc.) Paolo G. Radaelli, Oxford, Sept 2003

  25. Heitler-London Singlet Singlet (S=0) Triplet (S=1) Hund-Mulliken Singlet (Molecular orbital) } 1 2 2 1  Singlet (S=0) 1,2 1,2

  26. What if the “objects” dimerised? CuIr2S4½ holes/site“Octamers” MgTi2O41 electron/site“Helices” Paolo G. Radaelli, Oxford, Sept 2003

  27. CuIr2S4 • Y. Koyama ‡ • Yew-San Hor§ Sample synthesis, transport meas. • Valery Kiryukhin§ synchrotron data • Hiroki Ishibashi§|| • Sang-Wook Cheong§ • Y. Horibe†‡§ Electron Microscopy • C.H. Chen† • Matthias J. Gutmann* Neutron diffraction • Richard M. Ibberson* PDF analysis * ISIS Facility, Rutherford Appleton Laboratory † Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974, USA ‡ Department of Materials Science and Engineering, Waseda University, Japan § Department of Physics and Astronomy, Rutgers University New Jersey, USA. || Department of Materials Science, Osaka Prefecture University, Osaka, Japan. Paolo G. Radaelli, Oxford, Sept 2003

  28. CuIr2S4: Charge Ordering and spin pairing. • The copper iridium thiospinel CuIr2S4 is a very young relative of magnetite, since it was synthesized for the first time in 19941. • It is reminiscent of Fe3O4 in that it is half-filled and has a coupled M-I and structural transition (at 230 K), but with one striking difference: it undergoes a Pauli paramagnet-to-diamagnet phase transition at the same time2. 1S. Nagata et al., Physica B 194-196 (1994) P. 1077. 2 T. Furubayashi et al., J.Phys.Soc.J 63 (1994) p. 3333. Paolo G. Radaelli, Oxford, Sept 2003

  29. Magneto-transport in CuIr2S4 T. Furubayashi et al., J.Phys.Soc.J 63 (1994) p. 3333

  30. N1+ modes +5 -2 -7 9,5 3,5 -7 -11 +1 +13 -8 -6 +3 15,3 +1 +6 +8 8,12 -3 6,10 8,2 +8 +12 +6 +10 6,4 -4 -16 c -2 -14 +7 2,14 4,16 -4 -5 +4 +2 11,7 -5 -9 1,7 +3 +15 13,1 -1 a Example of Mode analysis I41/amdP21/m

  31. HRPD Data

  32. PGR et al., Nature 416 (2002) p. 155.

  33. CuIr2S4: Irradiation effect1. 1H. Ishibashi et al., PRB 66 (2002) 144424.

  34. CuIr2S4: Conclusions. • The crystal structure of CuIr2S4 at low temperatures accounts well for the observed transport and magnetic properties. Band structure calculations indicate HM rather than HL singlets (a Peierls rather than a spin-Peierls transition). • The ‘Octamer-based’ description of the spinel crystal structure is simple and elegant. Yet, the underlying CO structure represents a step up in complexity with respect to all previously known arrangements. • X-ray irradiation destroys the octamers but preserves the dimers. Paolo G. Radaelli, Oxford, Sept 2003

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