『磁性薄膜・多層膜を究める：キャラクタリゼーションから新奇材料の創製へ』
2011. 10. 14-15
- 放射光を用いたキャラクタリゼーション -
マンガン系人工超格子における
電荷・磁気状態の研究
…….
La3+Mn3+O3
Sr2+Mn4+O3
[(LaMnO3)m(SrMnO3)m']n
MnO2
SrO
MnO2
SrO
MnO2
LaO
MnO2
LaO
MnO2
4+
4+
3.5+
3+
3+
Condensed matter research center (CMRC)
Photon Factory, IMSS, KEK
Outline
中尾裕則
・研究背景
・放射光を用いた薄膜、人工格子の研究について
・中性子磁気散乱による磁気構造の研究の現状
(LaMnO3)2(SrMnO3)2 の巨大磁気抵抗効果
Substrate
人工超格子：自由な積層構造の設計による物性制御
結晶 (ABO3)
stacking direction
c
多様な物性
誘電体
強磁性体
反強磁性体
超伝導体
ペロブスカイト構
造
A'B'O3
ABO3
Substrate:SrTiO3
巨大磁気抵抗効果
電気磁気効果
任意の積層構造の作製
電荷・スピン・軌道・格子の制
御
新奇物性の探索や、
自由なデバイス設計の可能
性
ヘテロ界面で作り出される新たな電子
状態
人工超格子: [(LaMnO3)m(SrMnO3)m']n
c
Perovskite structure
(m,n) = (4,2)
Sr2+Mn4+O3 G-type AF
eg
stacking direction
t2g
n
Mn4+
Band insulator
m'
Sr2+Mn4+O3
La3+Mn3+O3
m
La3+Mn3+O3
A-type AF
eg
t2g
Mn3+
Substrate: SrTiO3
Cubic: a = 3.905Å
Mott insulator
電荷変調構造の制御
新奇物性？
人工超格子: [(LaMnO3)m(SrMnO3)m']n
[(LaMnO3)m(SrMnO3)m]n
(m,n)
(1,96)
(2,48)
(4,24)
(8,12)
(16,6)
(32,3)
Insulator
m increases!
LaMnO3
Mn3+
SrMnO3
Mn4+
Mn3.5+
Metal
?
Mn valence state / interface state
T. Koida et al., PRB 66 (2002)
Specific character in superlattice
 Resonant x-ray scattering study of the superlattices
ion
to clarify the charge distribution of the Mn
 Evaluation of the superlattice structures
Experiments
 Synchrotron x-ray scattering
 Diffraction pattern along the stacking direction at 6.52 keV
Superlattice structure (atomic coordinations)
 Energy dependence of the scattering intensity
near Mn K-edge（~ 6.55 keV）
Charge distribution of Mn ion
X-ray anomalous scattering factor
X-ray anomalous scattering factor
of Mn ion
f’(E)
f’’(E)
Mn3+
Mn4+
3 eV
Difference
 Energy dependence of the scattering intensity
near Mn K-edge（~ 6.55 keV）
Charge distribution of Mn ion
X-ray anomalous scattering
SrTiO3
+2 +3
-3
+1
-2
+2
[(LaMnO3)m(SrMnO3)m]n
+3
(m,n) = (8,6)
Thickness: ~360Å
SrTiO3
E=6.52 keV
m
LaMnO3 dLa
SrMnO3 dSr
(001)
-5 -4
-3 -2
-1
+1
(002)
-1
(001)
Intensity (a.u.)
SrTiO3
Crystal structure of superlattice
-1
-3
-2
n
Laue function
SrTiO3
Structural deviation near interface
Substrate scattering
+1
+2
+3
H. Nakao et al., JPSJ 78 (2009)
024602.
-3
-2
(001)
-1
SrTiO3
[(LaMnO3)m(SrMnO3)m]n
+1
+2
+3
Degree of charge ordering
(stacking direction)
c
Mn4+
Mn3+
Rectangle Alpha Sine No charge
wave ordering
(m,n) = (8,6)
Insulator vs. Metal
Quality of stacking
structure
Conductivity
H. Nakao et al., JPSJ 78 (2009)
024602.
Insulator
(FI)
Sample quality: SrTiO3 vs. LSAT
H. Yamada (AIST)
(200)
(200)-1
(La0.3Sr0.7)(Al0.65Ta0.35)O3
(LSAT)
(100)+2
Average lattice constant
(100)+1
SrTiO3 (STO)
(100)
Lattice matching between film and substrate
[(LaMnO3)m(SrMnO3)m]n
[(LaMnO3)m(SrMnO3)m]n
AFI
LSAT
FI
m
Mag.
field
LaMnO3 SrMnO3
FM
m ≦ 4:
Large negative magneto-resistance
Substrate LSAT
This is new phenomenon in film
system.
not reported in the bulk
Study project in CMRC
 Synchrotron radiation
Resonant and non-resonant x-ray
scattering
Mn valence distribution
Stacking structure
SR
Resonant soft x-ray scattering
Resonant magnetic scattering
Mn3d – O2p orbital hybridization
Modulation of electronic structure
Depth resolved XAS, XMCD (雨宮)…
 Neutron
Magnetic scattering (東北大 岩
佐)
Reflectivity (JAEA 武田)
 J-PARC
 Muon
Ultra-slow muon
Muon
Neutron
(200)
(100)
T = 5K vs. 300K
(LaMnO3)2(SrMnO3)2
0 T vs. 7.5 T
at T = 5K
(200)+1
(100)+2
(200)-1
6.52keV
(100)+1
(100)-2
(100)-1
Crystal structure in superlattice
Magnetic effect for Mn valence state
(200)
(100)
(200)+1
(100)+2
(200)-1
6.52keV
(100)+1
(100)-2
(100)-1
studied by resonant x-ray scattering
at T = 5K
中性子磁気散乱による
人工格子の磁性研究の可能性
TOPAN(6G) at JRR-3 in Tokai
Tohoku Univ. :
Iwasa
K.
L2S2/LSAT
(LaMnO3)2(SrMnO3)2
12 samples
b
a
3cmx1.5cmx400Å
< 0.3x0.3x0.3mm3
Magnetic scattering
at (100)±１
No signal at (100)-1
Magnetic scattering: L2S2/LSAT
Periodicit
y
LaMnO3
SrMnO3
(100)-2
Simple AFM
RMXS at Mn L2,3-edge: L5S5
p
s
磁気散乱強度の温度依存性
N
S
(000)+1
+2
久保田
（JAEA)
+3
Magnetic component Ip
Form factor
X-ray anomalous scattering
factor
LaMnO3
XAS
K-K trans.
SrMnO3
Study of artificial superlattice

Mn valence distribution
Stacking structure (crystal structure)
Resonant and non-resonant x-ray scattering
 Magnetic structure
Neutron magnetic scattering / Reflectivity
Resonant magnetic x-ray scattering: Mn L-edge
Mag.
field
FM
L5S5
FI
SrMnO3
L2S2
AFI
LSAT
m
LaMnO3
[(LaMnO3)m(SrMnO3)m]n
Collaborator
Y. Yamasaki, J. Okamoto, T. Sudayama, Y. Murakami
Condensed Matter Research Center / Photon Factory, IMSS, KEK
K. Iwasa
Depertment of Physics, Tohoku University
M. Kubota, Y. Takeda Japan Atomic Energy Agency
Neutron
J. Nishimura, A. Ohtomo, T. Fukumura, and M. Kawasaki
Institute for Materials Research (IMR), Tohoku University
T. Koida
ERATO, Japan Science and Technology Corporation
H. Yamada, A. Sawa
Nanoelectronics Research Institute, AIST
Photon