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Physics of multiferroic hexagonal manganites RMnO 3

Physics of multiferroic hexagonal manganites RMnO 3. Je-Geun Park Sungkyunkwan University. KIAS 29 October 2005. Outline. Introduction Part 1: Phonon scattering due to short-ranged spin fluctuations of YMnO 3

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Physics of multiferroic hexagonal manganites RMnO 3

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  1. Physics of multiferroic hexagonal manganitesRMnO3 Je-Geun Park Sungkyunkwan University KIAS 29 October 2005

  2. Outline • Introduction • Part 1: Phonon scattering due to short-ranged spin fluctuations of YMnO3 • Part 2: Direct evidence of coupling among spin, lattice, and electric dipole moment for YMnO3 and LuMnO3 • Part 3: Doping and Pressure effects on the magnetic structure • Summary

  3. Ferromagnetism Ferroelectricity Fe3O4 PbTiO3 What is multiferroic behavior? Examples : Ni3B7O13I, BiMnO3, BiFeO3, RMnO3 (R=Ho-Lu, Sc, Y), RMn2O5(R=Tb,Dy)

  4. Renaissance of Multiferroic N. A. Spaldin and M. Fiebig Science (2005) • Multiple State Memory Device • Write E / Read M • Write M / Read E • Magnetic valve • Data storage • Tunable sensors • Spin transistor Key Issue : Coupling among P, M, and e

  5. Control of Magnetic Phase by E HoMnO3 T. Lottermoser et al., Nature (2004)

  6. Controlling Polarization by Magnetic field N. Hur, S.-W. Cheong et al., Nature (2003) A similar demonstration was presented by Prof. Tokura’s group for TbMnO3. see T. Kimura Nature (2003)

  7. Multiferroic Hexagonal Manganites RMnO3

  8. Summary of properties of Hexagonal Manganites

  9. Multiferroic Behavior Antiferromagnetic Ferroelectric Wo-chul Yi et al.Appl. Phys. Lett., (1998) T.Katsufuji et al., PRB (2001)

  10. O1 O3 O4 O2 AMnO3 Hexagonal structure Othorhombic structure

  11. x2-y2 3z2-r2 eg eg 1.7 eV : IR 5~6 eV : PES 3z2-r2 xy x2-y2 xy t2g t2g xz yz xz ,yz Jahn-Teller active Jahn-Teller inactive Crystal field level of Mn3+ Hexagonal manganites Orthorhombic manganites J. S. Kang, JGP et al., PRB 71, 092405 (2005)

  12. Origin of FE transition?

  13. Origin of FE transition? The ferroelectric instability is due to Y-O displacement, which is accompanied by MnO5 rotation. See B. van Aken et al., Nature Materials (2004)

  14. O1 Mn O3 O4 O2 2D Triangular lattice of Mn moments

  15. Irreducible representations G1 representation G2 representation G4 representation G3 representation A. Munoz et al., PRB (2000)

  16. Magnetic structure YMnO3 Junghwan Park, JGP et al., Applied Physics A (2002)

  17. Inelastic Neutron Scattering of YMnO3 J=3 meV, a=0.95, D=0.03 meV Junghwan Park, JGP et al., Phys.Rev.B (2003)

  18. Spin dynamics of single crystal YMnO3 T. Sato et al., Phys.Rev. B (2003) J1=-3.4(2) meV , J2=-2.02(7) meV J’1-J’2=0.014(2) meV D1=-0.028(1) meV D2=0.0007(6) meV

  19. Questions • What are the effects due to the short-ranged magnetic fluctuations on their physical properties? • How are the magnetic and electric dipole moments coupled to one another? • What are doping effects on the magnetic properties?

  20. Part 1: Phonon scattering due to short-ranged spin fluctuations of YMnO3 Phys. Rev. B 68, 1004426 (2003) Phys. Rev. Lett. 93, 177202 (2004)

  21. Part 1 Geometrical frustration Triangular lattice with AF interaction YMnO3

  22. Part 1 HANARO 30MW Diffuse scattering seen in YMnO3 well above TN: Evidence of short ranged magnetic correlation, i.e. spin liquid phase Data taken at HANARO, Korean research reactor

  23. Part 1 : the distance between nearest neighboring spins : measured difference curve : the form factor of Mn3+ E.F. Bertaut et al. Solid State Commun. 5, 279(1967) 80 K Data subtracted off by the 300 K data

  24. Part 1 Fitting of I(Q)/F2(Q) of YMnO3 Junghwan Park, JGP et al., Phys.Rev.B (2003) Å Å

  25. Part 1 Spin liquid phase in the paramagnetic phase

  26. Part 1 Additional scattering of acoustic phonons due to spin liquid phase

  27. Part 1 YMnO3 (Å) P. Sharma, JGP et al., PRL (2004)

  28. Part 2: Direct evidence of coupling among spin, lattice, and electric moments for YMnO3 and LuMnO3 Phys. Rev. B Rapid Comm. 71, 180413 (2005)

  29. Part 2 ey ex plane z=0 plane z=1/2 Г1 magnetic structure Temperature dependence of moment and lattice constants (Å) c (Å) Junghwan Park, JGP et al., Applied Physics A (2002)

  30. Part 2 Temperature dependence of a, c, and volume up to 1200 K : High temperature neutron diffraction data HT: P 63/m mc LT: P 63 cm J. Park, JGP (unpublished)

  31. Part 2 SIRIUS（High resolution and high intensity powder diffractometer）@ KENS

  32. Part 2 Refinement results : TOF diffractometer SIRIUS at KEK

  33. Part 2 O1 Mn O3 O4 O2 Refinement results Temperature dependence of atom positions Å (Å) (Å) (Å)

  34. Part 2 u KEK YMnO3 results

  35. Part 2 u=-a-b Mn O4 O3 b O4 a

  36. Part 2 Coupling among magnetic moments, lattice, electric dipole moments Y : 3+ Mn ; 3+ O : 2- Seongsu Lee et al., PRB (2005)

  37. Part 3: Doping and Pressure Effects on the magnetic properties Phys. Rev. B 72, 014402 (2005) JETP 82, 212 (2005)

  38. Part 3 O1 Mn O3 O4 O2 2D Triangular lattice of Mn moments

  39. Part 3 Doping effects of (Er1-xYx)MnO3

  40. Irreducible representations Part 3 1 representation 2 representation 4 representation 3 representation YMnO3 ErMnO3

  41. Magnetic structure of (Er1-xYx )MnO3 Part 3

  42. Part 3 O1 Mn O3 O4 O2 2D Triangular lattice of Mn moments

  43. Part 3 Mn-site doping effects in Y(Mn,X)O3 with X=Zn, Al, and Ru Mixing of G1 and G2 structures

  44. Part 3 External Pressure Effects on YMnO3 • Mixing of magnetic structure Γ1 Γ1+ Γ2: for 2.5 GPa, μord = 1.52 μB with F=60o at 10K: • Diffuse scattering enhanced with pressure

  45. Summary • Spin liquid phase evidenced by the diffuse peaks scatters acoustic phonons through unusually strong spin-phonon coupling, which then gives rise to a significant reduction in thermal conductivity in the paramagnetic phase. • We have shown that below TN the magnetic moments of YMnO3 and LuMnO3 are strongly coupled to the lattice degrees of freedom with further coupling to the ferroelectric moments. However, an underlying microscopic mechanism for such a coupling is not clear yet. • The magnetic ground states of RMnO3 are so subtle that even a small doping can induce mixing between different magnetic states.

  46. Acknowledgements • Seongsu Lee, Misun Kang, Jung Hoon Han, H. Y. Choi, A. Pirogov: Sungkyunkwan University • Changhee Lee: KAERI, Korea • W. Jo: Ewha Womans University, Korea • S-W. Cheong: Rutgers University, USA • T. Kamiyama: KEK, Japan • R. Bewley: ISIS, UK • Jeongsu Kang: Catholic University, Korea • D. Kozlenko: Frank Laboratory, Russia

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