Inst. Mat. Structure Science-Symposium ’08 (Tsukuba, 16th, Oct. 2008）

Synchrotron X-ray Studies of Magnetic Order
ARIMA Taka-hisa
Inst. Multidisciplinary Res. Adv. Mat., Tohoku Univ.
& RIKEN SPring-8 CenterX-ray Studies of Magnetic Order: OVERVIEW•Resonance: Element-specific Investigation•LS Separation•Small Focus•High Q-resolution•No Killer Element
Complementary to Neutron Scattering•Magnetic Circular Dichroism in Ferromagnetic Matter•Magnetic Diffraction in Magnetic Matter
9Spectroscopy: Wave Function
9Polarization Analysis: LS Separation
9Circular Polarization: Spin Chirality•Superlattice Modulation in Frustrated Magnet•Nonreciprocal Directional Dichroism & Scattering:Magnetism at Non-centrosymmetric Sites
PEEM, Magnetic Compton, Auger, Moessbauer, …

1st Topic
Magnetic Structure and 5d Orbital State in Sr2IrO4Collaborators
B. J. Kim, S. Fujiyama, J. Matsuno,
H. Takagi (Univ. Tokyo & RIKEN ASI)
T. Komesu, S. Sakai, T. Morita,
H. Ohsumi (RIKEN SP8)

B. J. Kim et al., submitted
S. Fujiyama et al., unpublished

S. Fujiyama

Resonant Magnetic X-ray Scattering
4s, 4p L-edge resonant x-ray scatteringwould provide useful information
on magnetic d electrons.

3dK

L3(La,Sr)3Mn2O7 (x=0.475)
001 reflection
SRS, UK

L2

2p3/2
2p1/2
1s
S.B. Wilkins et al., Phys. Rev. Lett. 90, 187201 (2003)

Hard x-ray is a powerful tool for 5d system
E 2p [eV]

λ [A]

E 3d

λ [A]

3d TM

450~900

14~28--

4d TM

2.2k~3.4k

3.6~5.6--Lanthanides

5.7k~8.9k

1.3~2.2 450~1500

5d TM

9.6k~11.9k 1.0~1.3Actinides

15.9k~0.8~ScTi

VCr Mn FeCoYZrNb Mo Tc(Ln) HfTaW

ReRu Rh
OsIr-8~28-

3.2k~3.6k 3.4~3.8

NiCu

Pd AgPtAuStrong LS
Strong Ligand Field
Wide BandSr2IrO4
Distorted K2NiF4-type Structure (I41/acd)

2a × 2a × 2c

Ir4+: 5d5 Low-Spin

Semiconducting

Magnetic Order
below 230K

G. Cao et al., Phys. Rev. B 57, R11039 (1998)

No Neutron Data

Meta-magnetism(~0.15μB/Ir)

Resonant Magnetic Diffraction:
Determination of Magnetic Structure
Intensity (arb. unit)

Net momentof each layer(1 0 L)(0 1 L)

18192021222324

L (r. l. u.)cSPring-8 BL29XUL & BL19LXU

ba1mm

1.00.8(1 0 22) reflection
absorption

L3 edge

L2 edge

0.6
0.4
0.2
0.0
11.15

11.20

11.25

12.80

Photon Energy (keV)

12.85

12.90

Absorption Intensity (arb. unit)

Scattering Intensity (arb. unit)

Resonant Spectrum: Wave Function
Ir 5dεJ eff ≡ −L + S
Jeff=1/2
Jeff=3/2

No Contribution
to MXS

J=3/2 (L3)Ir 2p
J=1/2 (L2)Spin-Orbital Coupled State!
Also see B. J. Kim et al., Phys. Rev. Lett. 101, 076402 (2008).

Possible Impact of Strong LS Coupling in 5d system
Difference in Band Structure from 4d System
Rh 4dγ(eg)Ir 5dγ(eg)Jeff=1/2

Rh 4dε(t2g)

Ir 5dε(t2g)

O 2p

O 2p

Sr2RhO4: Metal

Jeff=3/2

Sr2IrO4: Mott Insulator

Possibly Good Arena for Spintronics or Magneto-optics

U2nd Topic
Phase Transition & Spin-Lattice Couplingin Multiferroic RMnO3
Collaborators
H. Sagayama, N. Abe, K. Taniguchi (IMRAM Tohoku Univ.)
T. Kimura, T. Goto, Y. Yamasaki, D. Okuyama,
Y. Tokura (Univ. Tokyo & ERATO JST & RIKEN ASI)
H. Sagayama
T. Inami, K. Ishii, Y. Murakami (JAEA)
Y. Wakabayashi, H. Sawa (KEK-PF)
H. Ohsumi, S. Sakai (RIKEN SP8)
T. Kimura et al., Phys. Rev. B68, 060403(R) (2003).
T. Kimura et al., Nature 426, 55 (2003).
T. Arima et al., Phys. Rev. B72, 100102R (2005).
T. Arima et al., J. Phys. Soc. Jpn. 76, 023602 (2007).

Mechanisms of Spin-driven Ferroelectricity
Si×Sj

Cycloid

Frustrated Magnet

Ferroelectricity

Proper Screw

T. Arima, JPSJ (2007)+αCommensurate AFM+αH. Katsura et al., PRL (2005)

Ferroelectricity

Si･Sj(Improper)
Ferroelectricity

Such an (anti)ferromagnetic ferroelectric is often classified into ‘Multiferroic’.

Role of Diffraction Studies in Multiferroics
Giant magnetoelectric effect in a frustrated system is nothing
but a transition between nearly-degenerate different magnetic
phases, some of which accompany ferroelectricity.

Diffraction Study•Magnetic Structure•Phase Transition•Spin-Lattice CouplingFirst Synchrotron X-ray Investigation on TbMnO3

Lattice Modulation
with 2qm

BL-4C KEK-PF in 2002T. Kimura et al., Phys. Rev. B68, 060403(R) (2003).
T. Kimura et al., Nature 426, 55 (2003).

Lattice Modulation in Spiral Magnets(a) Proper Screwr
Qs = 0rr
Qs = Qmrr
Qs = 2Qm(b) Screw Cone(c) Cycloid(d) Elliptical Cycloid(e) Cycloid Cone

T. Arima et al., J. Phys. Soc. Jpn. 76, 023602 (2007).

Ferroelectricity

SuperlatticeH-induced P rotation (“flop”) in TbMnO3

Collinear Sinusoidal
PECycloid???

T. Kimura et al., Nature 426, 55 (2003)

What sort of magnetic phase appears in the P∥a phase?

Incommensurate-Commensurate Transition upon P-Flop
TbMnO3 H//b50

TN 1

40
AFM(IC)-PE

30

TC20
AFM-FE(P//c)

Polarization [μC/m2]

024
Magnetic Field [T](P//a)
6600

5T=4 K

4Pc

400

32Mb

200

10.70

0T~5 K

0.6
q

0.5
0.4
0.3
0.2

SPring8 BL22XU
T. Arima et al., Phys. Rev. B72 100102R (2005).

024

Magnetic Field [T]6

Magnetization [μB/Mn]

10

Two Models of Magnetic Structure in P∥a PhasebH

qmag=1/4aCommensurate AFM
with Q=1/4

Cycloid with moments inthe ab plane
Supported by spin-polarized neutron diffraction
Y. Yamasaki et al., PRL 101, 097204 (2008)

Detection of spin chirality is crucial.
M. Blume, Phys. Rev. 130, 1670 (1963).

1. Spin-polarized Neutron
2. Circularly-polarized X-ray
M. Blume & D. Gibbs, Phys. Rev. B37, 1779 (1988).

Summary
Magnetic structures below and above Neel temperature aswell as the L/S ratio and wave function of Ir ion in Sr2IrO4
have been determined by x-ray magnetic scattering.
 Magnetic
wave vector and spin-lattice coupling in
multiferroics have been investigated through superlatticereflections.
 Spin chirality can be investigated by circularly polarized x-ray.
In regard to resonant magnetic scattering,Resonant magnetic scattering for 4d systems with photons of
2.2~3.5 keV would provide much useful information.
Thank you for your Attention!!