Physics of multiferroic hexagonal manganitesRMnO3Je-Geun ParkSungkyunkwan UniversityKIAS 29 October 2005

OutlineIntroductionPart 1: Phonon scattering due to short-ranged spin fluctuations of YMnO3Part 2: Direct evidence of coupling among spin, lattice, and electric dipole moment for YMnO3 and LuMnO3Part 3: Doping and Pressure effects on the magnetic structureSummary

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

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

T. Lottermoser et al., Nature (2004)HoMnO3Control of Magnetic Phase by E

Controlling Polarization by Magnetic fieldN. Hur, S.-W. Cheong et al., Nature (2003)A similar demonstration was presented by Prof. Tokuras group for TbMnO3. see T. Kimura Nature (2003)

Multiferroic Hexagonal Manganites RMnO3

Summary of properties of Hexagonal Manganites

antiferromagnetic ordering temperature (K)ferroelectric ordering temperature (K)a ()c ()ScMnO3129~ 9005.83311.17YMnO3809146.13911.39HoMnO376~ 9006.14211.42ErMnO3808306.11211.40TmMnO386~ 9006.09211.37YbMnO3879836.06211.36LuMnO396~ 9006.04211.37

T.Katsufuji et al., PRB (2001)Wo-chul Yi et al.Appl. Phys. Lett., (1998)FerroelectricAntiferromagneticMultiferroic Behavior

Hexagonal structureOthorhombic structureAMnO3

Crystal field level of Mn3+Orthorhombic manganitesHexagonal manganitesJ. S. Kang, JGP et al., PRB 71, 092405 (2005)

Origin of FE transition?

antiferromagnetic ordering temperature (K)ferroelectric ordering temperature (K)a ()c ()ScMnO3129~ 9005.83311.17YMnO3809146.13911.39HoMnO376~ 9006.14211.42ErMnO3808306.11211.40TmMnO386~ 9006.09211.37YbMnO3879836.06211.36LuMnO396~ 9006.04211.37

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)

2D Triangular lattice of Mn moments

Irreducible representationsA. Munoz et al., PRB (2000)

Magnetic structure YMnO3Junghwan Park, JGP et al.,Applied Physics A (2002)

G1G3a () = 6.1208(1)b () = 11.4015(2)V (3) = 369.91(1)a () = 6.1208(1)b () = 11.4015(2)V (3) = 369.91(1)Magnetic Moment (mB)3.30(2)Magnetic Moment (mB)3.25(2)Reliability factorsRp = 5.79 % Rwp = 7.93 %Rmag = 7.88 %c2 = 2.70Reliability factorsRp = 5.83 % Rwp = 7.98 %Rmag = 7.35 %c2 = 2.74

Inelastic Neutron Scattering of YMnO3Junghwan Park, JGP et al.,Phys.Rev.B (2003)J=3 meV, a=0.95, D=0.03 meV

Spin dynamics of single crystal YMnO3J1=-3.4(2) meV , J2=-2.02(7) meVJ1-J2=0.014(2) meVD1=-0.028(1) meVD2=0.0007(6) meV

QuestionsWhat 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?

Part 1:

Phonon scattering due to short-ranged spin fluctuations of YMnO3Phys. Rev. B 68, 1004426 (2003)Phys. Rev. Lett. 93, 177202 (2004)

Geometrical frustrationTriangular lattice with AF interactionPart 1YMnO3

Diffuse scattering seen in YMnO3 well above TN:

Evidence of short ranged magnetic correlation, i.e. spin liquid phaseData taken at HANARO, Korean research reactorPart 1

80 K Data subtracted off by the 300 K dataPart 1

Fitting of I(Q)/F2(Q) of YMnO3Part 1Junghwan Park, JGP et al.,Phys.Rev.B (2003)

Spin liquid phase in the paramagnetic phasePart 1

Additional scattering of acoustic phonons due to spin liquid phasePart 1

YMnO3P. Sharma, JGP et al., PRL (2004)()Part 1

Part 2:

Direct evidence of coupling among spin, lattice, and electric moments for YMnO3 and LuMnO3Phys. Rev. B Rapid Comm. 71, 180413 (2005)

()c ()Junghwan Park, JGP et al., Applied Physics A (2002) Temperature dependence of moment and lattice constants Part 2

Temperature dependence of a, c, and volume up to 1200 K : High temperature neutron diffraction dataHT: P 63/m mcLT: P 63 cmPart 2J. Park, JGP (unpublished)

SIRIUSHigh resolution and high intensity powder diffractometer@ KENSPart 2

Refinement results : TOF diffractometer SIRIUS at KEKPart 2

Temperature dependence of atom positionsRefinement results ()()()Part 2

KEK YMnO3 results Part 2

Part 2

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

Part 3:

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

2D Triangular lattice of Mn momentsPart 3

Doping effects of (Er1-xYx)MnO3Part 3

Irreducible representationsPart 3YMnO3ErMnO3

Magnetic structure of (Er1-xYx )MnO3Part 3

2D Triangular lattice of Mn momentsPart 3

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

Mixing of magnetic structure 1 1+ 2: for 2.5 GPa, ord = 1.52 B with F=60o at 10K: Diffuse scattering enhanced with pressurePart 3External Pressure Effects on YMnO3

SummarySpin 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.

AcknowledgementsSeongsu Lee, Misun Kang, Jung Hoon Han, H. Y. Choi, A. Pirogov: Sungkyunkwan UniversityChanghee Lee: KAERI, KoreaW. Jo: Ewha Womans University, KoreaS-W. Cheong: Rutgers University, USAT. Kamiyama: KEK, JapanR. Bewley: ISIS, UKJeongsu Kang: Catholic University, KoreaD. Kozlenko: Frank Laboratory, Russia