Toward Electric Control of Magnetism

Transcription

1 Toward Electric Control of Magnetism Collaorators Yoshi Tokura Dept of Appl hys, Univ Tokyo Correlated Electron Research Center (CERC), AIST and ERATO Multiferroics roject,jst Univ. Tokyo Y. Yamasaki, T. Goto, Y. Shimada,S. Seki, Y. Onose (Dept Appl hys) K. Hirota, M. Matsuura (ISS) Tohoku Univ. T. Arima, H. Sagayama M. Kawasaki Osaka Univ. T. kimura Correlated Electron Research Center (CERC), AIST H. Yamada, M. Kawasaki*, ERATO Multferroics roject N. Kida, Y. Tokunaga, H. Murakwa, T. Kagawa, Y. Takahashi, R. Shimano, J-. He, Y. Kaneko,

2 Cross-correlation phenomena with correlated electrons magnetism electricity cross-correlation spin correlated electrons charge conductiitiy polarization magnetic field/light heat orital light magnetization electric field/current Correlated eletrons with multi-degrees of freedom can host the cross-correlation phenomena. optical response heat/magnetic field

3 Magneto-electric effect ierre Curie s Conjecture(1894) There should e materials whose magnetism is induced y electric field and whose polarization y magnetic field. electric control of magentism M α =G βα E β magnetic control of electricity α =G αβ B β Oservation on Cr 2 O 3 I.E.Dzyaloshinskii, Sov.hys.-JET 10, 628 (1959) D.N.Astrov, Sov.hys.-JET 11, 708 (1960) spin-orit interaction Biot-Savart s law I H orit S i M = i eri S i = E i er i

4 Importance of Multiferroics electric field magnetic field M olarization + - Electric field ferroelectics () Magnetization + - Magnetic field ferromagnet (M) M olarization + - multiferroics ( M) Magnetic field Magnetization + - Electric field

5 Sujects to e pursued in science of multiferroics Exploratory materials sprial cycloidal & conical exchange-striction charge/orital ordering interfaces Magnetic control of electricity multi-critically competing phases magnetic control of ferroelectric domains Electric/optical control of magnetism electric control of spin helicity electric/optical control of magnetic domains Electrodynamics of magnetic properties opitical magneto-electric effect, toroidal-moment optics elctro-magnon or electrically driven spin excitations

6 How to produce ferroelectric state in magnetic state 1. Bi 3+ -or 2+ (A-site)-ased perovskites BiMnO 3 (BiFeO3), BiCoO 3 (Azuma et al.) ordered doule perovskite: Bi 2 NiMnO 6 (T CE =485K, T CM =140K) (Azuma et al.) 2. tricolor superlattice LaMnO3/SrMnO3/LaAlO3 (Yamada-Lottermoser), (La,Sr)MnO3/LaAlO3/SrTiO3 (Yamada-Ogawa) 3. charge-ordering on a specific chemical lattice LuFe2O4, ilayered manganites 4. transverse-spiral (cycloidal) spin order

7 Transverse spiral spin structure produces ferroelectricity. = ηe ij (S i S j ) η ea( t dp / Δdp ) / cos( θij doule-exchange η ea( t dp / Δdp ) 3 super-exchange / 2) L r S r t dp d-oritals U r j s //e ij Katsura-Nagaosa-Balatzky r p-oritals Δ dp RL 95, (2005) Mostovoy Sergienko-Dagotto d-oritals U L r S r z -z

8 Spin frustration and Spiral Spin Order J 1 =F, J 2 =AF RMnO 3 J 1 J 2 ferroelectric! in

9 Spiral spin structure produces ferroelectricity. (T,Dy)MnO 3 (single crystal) TMnO 3 35K c sinusoidal-collinear 30K paraelectric 15K 15K transverse-spiral (cycloidal) ferroelectric Kenzelman et al. RL95, (2005). Arima et al. RL 96,097202(2006)

10 Electric control of spin helicity L (4,0,2) (4,-q,1) (4,+q,1) q~0.27 polarized neutron scattering Neutron Flipper On S n Off S n (4,-1,1) (4,1,1) Q K i a Q K i (4,0,0) K K s c K s + c Intensity (counts / 100 sec.) (4, q, L) On Off (4, q, L) + (4, +q, L) (4, +q, L) + 9 K + c c E Sample c +V V L (r.l.u.) L (r.l.u.) Yamasaki et al. RL98, (2007).

11 Ellipticity in spiral spins scales with the polarization Ellipticity m c m + (4,+q,1) c c/2 0 Intensity (ar. units) I on ( I on +I off )/2 I off Temperature (K) T C I (10 3 counts / 100 sec.) (4,+q, L) 45K 36K 24K 9K L T N On Off Electric olarization (μc/m 2 ) = ηe ij (S i S j ) T C + T N Temperature (K) I on I off (10 3 counts/ 30 sec. )

12 Gigantic magnetoelectic effect in DyMnO 3 Kimura et al. Nature (2003); Goto et al., RL (2004) = ηe ij (S i S j ) //c (H=0) c spin spiral plane a //a (H//) H

13 Magnetoelectric phase diagram Kimura, Goto et al. RL (2004);RB(2005). icritical phase competition IC-to- IC no change of q-vector! c s // c s //a a s // c

14 roposed spin structures and ferroelectric polarization a c collinear a ~30 K ~30 K ~27 K a a c WF c a spiral c c spiral ~24 K a Eu x=0.2 Eu Y MnO c x=0.4 a spiral Y

15 Flop of spin spiral plan and polarization a c a spiral spin flop H a polarization flop c spiral c

16 Large fluctuation of spin-spiral plane? pramagnetic (paraelectric) fluctuation etween a and c spirals Temperature c a c spiral collinear c a a spiral Control parameter (H or x)

17 Dielectric response Electro-magnon Katsura-Nagaosa-Balatzky RL(07) Oscillator strength at ω = DJ (Q) c a 8 SJ1 = 2.4meV for TMnO 3 D = 4meV 2 c 0.2μC/cm oscillator strength c spiral I ( ) I oserved -1 4cm 12cm -1 E ω imenov et al. Nature hysics(2006) But, this is not such a Goldstone mode.

18 Electrically driven spin excitations Strongly E ω //a asorption and (0-10meV)

19

20 olarization (E ω //a) selection rule irrespective of spiral plane

21 ossile source of electric transition-dipole a FM coupling c AFM coupling δs// ac plane larger fluctuation ω ~ e ij (δs i δs j ) //c // //a Large spin fluctuation etween the neighoring sites along the c-axis may cause the strong electric-dipole activity ased on KNB model.

22 How to make multiferroics of all spin origin? S i p i add a uniform magnetization Conical spin structure with transverse spiral component = ηe ij (S i S j ) = 0 + Δ cos( qx) p i M S i

23 Spinel-type CoCr 2 O 4 as a conical ferrimagnet

24 Ferroelecticity, though tiny, in conical state Magnetization [μ Β /f.u.] 0.08 (a) T C-IC T s M//z (0.01T) 2 T c C/T [J/K 2 /mol] () olarization [μc/m 2 ] //y +E c -E c Magnetoelectric Field Cooling μ 0 H c =0.01T, E c =400kV/m ε//y 10kHz Dielectric constant Temperature [K]

25 olarization reversal upon magnetization reversal Magnetization [μ B /f.u.] olarization [μc/m 2 ] CoCr 2 O 4 M//z 27K 18K, (+E c,-h c ) 2 18K [μc/m 2 ] T 2-0.5T T (K) K, (+E c,+h c ) 27K, (+E c,+h c ) olarization [μc/m 2 ] M T 1 T = 2 M y z [001] [110] 18K x [110] Magnetic Field [T] Magnetic Field [T] -2 //y Time [second] H//z Yamasaki et al. RL (2006)

26 helical spins and polarization modulaton modulation of polarization

27

28 Rotating magnetic field Dynamo ased on spin current!

29 Rotation of spin-cone magnetic anisotropy Zeeman energy closure of spin-cone rotation of spin-cone

30 polarization flop/non-flop upon q-switching

31 Sujects to e pursued in science of multiferroics Exploratory materials sprial cycloidal & conical exchange-striction charge/orital ordering interfaces Magnetic control of electricity multi-critically competing phases magnetic control of ferroelectric domains Electric/optical control of magnetism electric control of spin helicity electric/optical control of magnetic domains Electrodynamics of magnetic properties opitical magneto-electric effect, toroidal-moment optics elctro-magnon or electrically driven spinexcitations

32 Spiral/chiral spin ojects as source of emergent properties vector spin chirality S i S j ----magnetic ferroelectricity toroidal moment r i S i ---- magneto-electric effect scalar spin chirality S i (S j S k ) --- anomalous Hall current, magnetization vortex real-space oservation of helical spin structr. y Lorenz TEM knife-edge dislocation (Fe,Co)Si Swill-roll like vortex FeGe ( MnSi?) Uchida et al. Science (2006) Uchida et al. (2007.9)