Physics of multiferroic hexagonal manganites RMnO3

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

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What is multiferroic behavior?
Examples Ni3B7O13I, BiMnO3, BiFeO3, RMnO3
(RHo-Lu, Sc, Y), RMn2O5 (RTb,Dy)
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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
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Control of Magnetic Phase by E
HoMnO3
T. Lottermoser et al., Nature (2004)
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Controlling Polarization by Magnetic field
N. Hur, S.-W. Cheong et al., Nature (2003)
A similar demonstration was presented by Prof.
Tokuras group for TbMnO3. see T. Kimura Nature
(2003)
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Multiferroic Hexagonal Manganites RMnO3
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Summary of properties of Hexagonal Manganites
antiferromagnetic ordering temperature (K) ferroelectric ordering temperature (K) a (Å) c (Å)
ScMnO3 129 900 5.833 11.17
YMnO3 80 914 6.139 11.39
HoMnO3 76 900 6.142 11.42
ErMnO3 80 830 6.112 11.40
TmMnO3 86 900 6.092 11.37
YbMnO3 87 983 6.062 11.36
LuMnO3 96 900 6.042 11.37
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Multiferroic Behavior
Antiferromagnetic
Ferroelectric
Wo-chul Yi et al.Appl. Phys. Lett., (1998)
T.Katsufuji et al., PRB (2001)
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AMnO3
Hexagonal structure
Othorhombic structure
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Crystal field level of Mn3

• Orthorhombic manganites

Hexagonal manganites
J. S. Kang, JGP et al., PRB 71, 092405 (2005)
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Origin of FE transition?
antiferromagnetic ordering temperature (K) ferroelectric ordering temperature (K) a (Å) c (Å)
ScMnO3 129 900 5.833 11.17
YMnO3 80 914 6.139 11.39
HoMnO3 76 900 6.142 11.42
ErMnO3 80 830 6.112 11.40
TmMnO3 86 900 6.092 11.37
YbMnO3 87 983 6.062 11.36
LuMnO3 96 900 6.042 11.37
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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)
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2D Triangular lattice of Mn moments
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Irreducible representations
A. Munoz et al., PRB (2000)
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Magnetic structure YMnO3
G1 ?G3
a (Å) 6.1208(1) b (Å) 11.4015(2) V (Å3) 369.91(1) a (Å) 6.1208(1) b (Å) 11.4015(2) V (Å3) 369.91(1)
Magnetic Moment (mB) 3.30(2) Magnetic Moment (mB) 3.25(2)
Reliability factors Rp 5.79 Rwp 7.93 Rmag 7.88 c2 2.70 Reliability factors Rp 5.83 Rwp 7.98 Rmag 7.35 c2 2.74
Junghwan Park, JGP et al., Applied Physics A
(2002)
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Inelastic Neutron Scattering of YMnO3
J3 meV, a0.95, D0.03 meV
Junghwan Park, JGP et al., Phys.Rev.B (2003)
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Spin dynamics of single crystal YMnO3
J1-3.4(2) meV , J2-2.02(7) meV J1-J20.014(2)
meV D1-0.028(1) meV D20.0007(6) meV
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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?

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Part 1 Phonon scattering due to short-ranged
spin fluctuations of YMnO3
Phys. Rev. B 68, 1004426 (2003) Phys. Rev. Lett.
93, 177202 (2004)
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Geometrical frustration
Part 1
Triangular lattice with AF interaction
YMnO3
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Part 1
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
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Part 1
80 K Data subtracted off by the 300 K data
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Part 1
Fitting of I(Q)/F2(Q) of YMnO3
Junghwan Park, JGP et al., Phys.Rev.B (2003)
Å
Å
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Spin liquid phase in the paramagnetic phase
Part 1
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Additional scattering of acoustic phonons due to
spin liquid phase
Part 1
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Part 1
YMnO3
(Å)
P. Sharma, JGP et al., PRL (2004)
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Part 2 Direct evidence of coupling among
spin, lattice, and electric moments for YMnO3 and
LuMnO3
Phys. Rev. B Rapid Comm. 71, 180413 (2005)
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Part 2
Temperature dependence of moment and
lattice constants
(Å)
c (Å)
Junghwan Park, JGP et al., Applied Physics A
(2002)
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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)
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Part 2
SIRIUS(High resolution and high intensity powder
diffractometer)_at_ KENS
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Refinement results TOF diffractometer SIRIUS at
KEK
Part 2
10K 300K
Y(1)z 0.2773(7) 0.2727(8)
Y(2)z 0.2318(6) 0.2320(7)
Mnx 0.3423(1) 0.3330(1)
O(1)x 0.3007(4) 0.3076(4)
O(1)z 0.1606(7) 0.1625(7)
O(2)x 0.6399(4) 0.6414(4)
O(2)z 0.3339(7) 0.3360(7)
O(3)z 0.4804(8) 0.4754(9)
O(4)z 0.0193(7) 0.0163(8)
Rwp 6.29 4.19
Rp 4.89 3.42
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Part 2
Refinement results
Temperature dependence of atom positions
Å
(Å)
(Å)
(Å)
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Part 2
KEK YMnO3 results
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Part 2
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Coupling among magnetic moments, lattice,
electric dipole moments
Part 2
Y 3 Mn 3 O 2-
Seongsu Lee et al., PRB (2005)
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Part 3 Doping and Pressure Effects on the
magnetic properties
Phys. Rev. B 72, 014402 (2005) JETP 82, 212
(2005)
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Part 3
2D Triangular lattice of Mn moments
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Part 3
Doping effects of (Er1-xYx)MnO3
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Irreducible representations
Part 3
YMnO3
ErMnO3
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Magnetic structure of (Er1-xYx )MnO3
Part 3
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Part 3
2D Triangular lattice of Mn moments
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Part 3
Mn-site doping effects in Y(Mn,X)O3 with XZn,
Al, and Ru
Mixing of G1 and G2 structures
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Part 3
External Pressure Effects on YMnO3

1. Mixing of magnetic structure G1? G1 G2 for 2.5
   GPa, µord 1.52 µB with F60o at 10K
2. Diffuse scattering enhanced with pressure

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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.

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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