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LOCAL PROBE STUDIES IN MANGANITES AND COMPLEX OXIDES

LOCAL PROBE STUDIES IN MANGANITES AND COMPLEX OXIDES V.S. Amaral 1 , A.M.L. Lopes 2 , J.P. Araújo 3 , P.B. Tavares 4 , T.M. Mendonça 3,5 , J. S. Amaral 1 , J.N. Gonçalves 1,5 , J.G. Correia 5,6 and IS390 Collaboration 1 Dep. Física and CICECO, Univ. Aveiro, 3810-193 Aveiro, Portugal;

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LOCAL PROBE STUDIES IN MANGANITES AND COMPLEX OXIDES

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  1. LOCAL PROBE STUDIES IN MANGANITES AND COMPLEX OXIDES V.S. Amaral1, A.M.L. Lopes2, J.P. Araújo3, P.B. Tavares4, T.M. Mendonça3,5, J. S. Amaral1, J.N. Gonçalves1,5, J.G. Correia5,6 and IS390 Collaboration 1Dep. Física and CICECO, Univ. Aveiro, 3810-193 Aveiro, Portugal; 2CFNUL, Univ. Lisboa, 1649-003 Lisboa, Portugal; 3Dep. Física and IFIMUP, Univ. Porto, 4169-007 Porto, Portugal; 4CQ-VR, UTAD, 5001-801 Vila Real, Portugal; 5CERN EP, CH 1211 Geneve 23, Switzerland; 6ITN, E.N. 10, P-2685 Sacavém, Portugal

  2. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  3. eg La3+ JT effect D - crystal field splitting t2g O2- Mn3+ -3d4 If only Mn3+ collective JT distortion O Introduction to Manganites Manganites base structure perovkite AMnO3 ( A=La, Pr, Nd &Ca, Sr ...) Doping with divalent ions (R-D)MnO3 Electron doping (charge and orbital) Structure Magnetic Interactions Mixed valence: Mn3+ : Mn4+

  4. CO/OO signatures Introduction to Manganites Magnetic - Electric Phase Diagram Pr1-xCaxMnO3 Small Ionic radii Pr3+ =1.30 Å, Ca2+ =1.34 Å -Orthorhombic structure for all x Small overlap betweenMn & Oorbitals -Insulator for all x Charge Order is stabilized over a broad range of compositions Mn3+/Mn4+localization in a ordered way

  5. Phase separation and complexity Ma et al, Phys Rev. Lett 95, 237210 (2005) Atomic-scale coexistence (La,Pr)5/8Ca3/8MnO3 Charge contrast: occupied and unnocupied states Clusters with CE type arrangement in the paramagnetic phase 20x10 nm Renner et al, Nature 416, 518 (2002) Bi0.24Ca0.76MnO3

  6. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  7. Multiferroic materials • Inversion symmetry breaking (charge-orbital related) • Dislocated spin density waves • Magneto-electric coupling Tb/YMn2O5Nature, 429, 392 (2004) Magnetic field induces a sign reversal of the electric polarization Nature Materials 3, 164, (2004)

  8. Perovskite phases octahedra Hexagonal phase Trigonal bipyramid Multiferroic manganites AMnO3 Van Aken , thesis univ. Groningen

  9. Inversion symmetry is broken = + Site centred CO Bond centred CO Ferroelectricity D.Efremov et al, Nature Materials, 3,853 (2004) J. Van den Brink, D.I. Khomskii, J. Phys. Cond. Matt 20, 434217 (2008) Charge ordered manganites New scenario for the Charge Ordered State Theoretical work predicts the possibility of local electric dipole moments in CO manganites Ferroelectricity due to Charge Ordering in Pr1-xCaxMnO3 New paradigm for ferroelectrics,but it has been hard to prove experimentally that electric polarization exists in CO Pr1-xCaxMnO3 (due to finite conductivity)

  10. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  11. Ei 1 |Ii, mi〉 L1  ,Q  E |I, m 〉 E 2 L2 |If, mf〉 Ef Local Probe Studies / Technique Two-Photon PERTURBED ANGULAR CORRELATION Hyperfine splitting Electricfield gradient / Magnetic hyperfine field Probe nucleus: Q– quadrupolar moment - magnetic moment Vzz- EFG principal component - Asymmetry parameter Bhf- Magnetic hyperfine field Time dependence gives access to splitting of hyperfine levels

  12. Local Probe Studies / Technique Two-Photon PERTURBED ANGULAR CORRELATION Samples implanted with radioactive 111mCd @ ISOLDE/CERN E=60 keV, Dose < 1012 at/cm2 111mCd:I=5/2 and t1/2= 85 ns Q=0.83 b and =-0.766 n Samples annealed @ T=700 ºC in air Cd @ Pr/Casite

  13. PROPOSAL TO THE ISOLDE COMMITTEE– INTC/P132 Add1IS390-Studies of Colossal Magnetoresistive Oxideswith Radioactive Isotopes Aveiro1, Dublin2, Leuven3, Lisboa4, Moscow5, Orsay6, Porto7, Sacavém8, Stuttgart9, Tokyo10, Tsukuba11 Vila Real12 and the ISOLDE/CERN13 Collaboration Spokesman: V. S. Amaral Contact person: J.G. Correia E. Alves8, T. Agne13, J.S. Amaral1, V.S. Amaral1, J.P. Araújo7, J. M. D. Coey2, N. A. Babushkina5, J.G. Correia8,13, H.-U. Habermeier9, A. L. Lopes1, A.A.Lourenço1, J.G. Marques4,8, T. M. Mendonça7, M. S. Reis1, E. Rita8, J.C. Soares4, J.B. Sousa7, R. Suryanarayanan6, P.B. Tavares12, Y. Tokura10,11, Y. Tomioka11, A. Vantomme3, J.M. Vieira1 and U. Wahl8.

  14. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  15. Local Probe Studies / Pr1-xCaxMnO3 system EXPERIMENTAL RESULTS Pr1-xCaxMnO3PAC Anisotropy Functions x=0.25 (NO CO) @ ≠ Temperature ≠ Ca (x) content @ RT

  16. Temperature dependence for samples outside CO region Vzz increases with decreasing T due to atomic vibrations (rms displacements) High temperature linear slope ~ -1.5(1)10-4 K-1 Local Probe Studies / Pr1-xCaxMnO3 system EFG principal component Vzz @ RT @ 896K

  17. Softening of vibration modes? Local Probe Studies / Pr1-xCaxMnO3 system Samples within CO region Same high temperature linear slope ~ -1.5(2)10-4 K-1 Anomalous Vzz(T) dependence approaching CO transition Charge order driven by the softening of a vibration mode?

  18. T* Local Probe Studies / Pr1-xCaxMnO3 system CO region, Vzz vs Temperature TCO Sharp increase of Vzz @ T< TCO Dropping @ T* (85 to 67 Vzz/Å-2 in 2K)

  19. T* TCO T* T* TCO Local Probe Studies / Pr1-xCaxMnO3 system CO region, Vzz vs Temperature TCO Sharp increase of Vzz @ T< TCO Dropping @ T*

  20. Local Probe Studies / Pr1-xCaxMnO3 system EFG and magnetic susceptibility

  21. Susceptibility Increase TC Local Probe Studies / Pr1-xCaxMnO3 system EFG sensitiveto atomic vibrations and critical fluctuations Local Spontaneous Polarization From NMR and PAC studies in Ferroelectrics

  22. Local Probe Studies / Pr1-xCaxMnO3 system Results Electric susceptibility / spontaneous polarization below TC x=0.35 ->TEDO=206 K, x=0.4 ->TEDO=218 K, x=0.85 -> TEDO=112 K compatible with first-order dielectric phase transition below Tco A.M.L. Lopes et al., Phys. Rev. Lett. 100, 155702 (2008)

  23. Piezoelectric Force Microscopy in Pr1-xCaxMnO3 system Local Ferroelectric response in Pr0.6Ca0.4MnO3 single crystal Piezoresponse Force Microscopy-hysteresis loop at room temperature: The piezoelectric contrast points to the existence of a local polar state A. L. Kholkin, I.K. Bdikin, CICECO; Univ. Aveiro

  24. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  25. LaMnO3+D (La3/(3+D)Mn3/(3+ D)O3) Only Mn3+ collective JT distortion Doping Mn3+1-2D/ Mn4+2DMIX-VALENCE Orthorhombic (O’) Strong JT distortion Antiferromagnetic D Mn3+/ Mn4+MIX-VALENCE Rhombohedric (R) No collective JT distortion Ferromagnetic

  26. h 0 LaMnO3+D PAC anisotropy functions @ RT hand Vzz as a function ofD Orthorrombic  Rhombohedric

  27. LaMnO3.12 Ferromagnetic Insulatorstate @ T<TC Rhombohedric  Orthorhombicphase transition ~ RT Phase coexistence in a broad range of T Polarons ? Polaron nature and evolution? Polarons responsible for FM INSULATOR state?

  28. PAC anisotropy functions @ ≠ T Coexistence of two local environments for all T Rho Rho crystallographic phase (x-ray) 318 K Macroscopic Rho + Orth phase coexistence (x-ray) Orth+Rho 197 K Orth crystallographic Phase (x-ray) Orth MHF for T<TC (TC=145 K)

  29. 31% Percolation threshold Percolation of the local environments Below percolation threshold distortions accommodate in a weakly JT distorted phase hand Vzz vs T % of u and d local environments Ort Rho % Ort R+O x-ray Smooth variation fu (and fd) Strong JT distortions in the Rho. Phase Polarons clusters start to form @ T*>776 K High T X-rays do not see distorted phase Random distributed polaron clusters

  30. Lightly doped La-Ca manganite The same physics? R to O* transitions on cooling Intermediate JT-orbital ordering transition to O structure J. B. Goodenough, 2003

  31. La0.95Ca0.05MnO3 T>900K One fraction; low  T=900K R to O* transition T<900K Two fractions: high/low Vzz Change ratio at T~750K Only minoritary fraction sensitive to JT transition

  32. La0.95Ca0.05MnO3 PAC very sensitive to charge distribution changes: Disproportionation?

  33. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  34. RMnO3 vs. R ionic radius Single phase RMnO3 samples (excepting LuMnO3 with traces of Lu2O3) Lu2O3

  35. Two EFG’s present in YMnO3 samples EFG1 f1~70% w0~120 Mrad/s EFG2 f2~30% w0~180 Mrad/s AFM FE Paramagnetic Ferroelectric Paraelectric YMnO3 vs. Temperature Hexagonal structure

  36. Two EFG’s present in EuMnO3 samples EFG1 f1~35-40% w0~120 Mrad/s EFG2 f2~60-65% w0~180 Mrad/s Paramagnetic and Paraelectric AFM EuMnO3 vs. Temperature Orthorhombic structure Inversion of the main EFG below 20K

  37. OUTLINE Manganites and intrinsic complexity Charge-ordering scenarios, phase separation Multiferroic systems Local Probe Studies Hyperfine technique: Perturbed Angular Correlations Probing electric fields in Pr1-xCaxMnO3 system Phase separation, polaron dynamics in LaMnO3+ and La1-xCaxMnO3 Multiferroics: RMnO3 Other oxide systems Perspectives

  38. 294.5K 48.6K 21.4K 19.2K AgCrO2 (111In probe): a new multiferroic

  39. Ag2NiO2 and analogous: Orbital physics vs Charge Order Valence(charge) changes in Ag and Ni avoiding Jahn-Teller distortion Like AgCrO2 111Ag and 111Cd/In probes for the 2 sites: more complete mapping of charge distributions

  40. CONCLUSIONS - Combined with other techniques and theoretical modeling, PAC brings new insights on current cutting edge research on solid state physics: correlated electrons systems. -The availability of different probes at Isolde allows tackling different situations: chemical compatibility and environments.

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