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Soft X-ray photoemission and Soft X-ray photoemission and magnetic circular dichroism of magnetic circular dichroism of
correlated systems and nano-materials correlated systems and nano-materials
Workshop on Frontier Science Using Soft X-Rays at the APSAugust 5-6, 2004, Argonne
A. Fujimori University of Tokyo
& JAERI, Spring-8
Y. Saitoh, S. Fujimori, T. Okane, Y. Takeda, K. Terai
T. Nakatani, Y. Muramatsu (JAERI, SPring-8)
J. Okamoto (NSRRC, Taiwan), K. Mamiya (KEK-PF)
M. Kobayashi, Y. Ishida, J.I. Hwang (U. Tokyo)
Expt at Photon Factory:
H. Wadati, M. Takizawa, H. Kumigashira, J. Okabayashi, M. Oshima (U. Tokyo)
Samples:
T. Matsuda, Y. Haga, E. Yamamoto (JAERI)
Y. Tokiwa, S. Ikeda, Y. Onuki (Osaka U.) UFeGa5, UGe2
M. Takano (Kyoto U.), Y. Takeda (Mie U.) SrRuO3
M. Tanaka, S. Ohya (U. of Tokyo) Ga1-xMnxAs
H. Saeki, H. Tabata, T. Kawai (Osaka U.) Zn1-xCoxO
Theory:
A. Tanaka (Hiroshima U.) multiplet calc.
H. Yamagami (Kyoto Sangyo U.) band-structure calc.
OutlineOutline
• Soft x-ray beamlines – JAERI beamline BL23SU at Spring-8– BL2C at Photon Factory
• Soft x-ray photoemission– ARPES of U compounds– Epitaxial oxide thin films
• Soft x-ray MCD– Ferromagnetic oxides– Ferromagnetic superconductor– Ferromagnetic semiconductors
Soft x-ray beamlines in Spring-8 Soft x-ray beamlines in Spring-8
Solid state: BL25 BL27:Photochemistry
Actinides: BL23
cylindrical mirror
177°
top view
cylindrical mirror
toroidal mirrorgrating exit slitspherical mirror
spherical mirror 177°entrance slit177°
cylindrical mirror
VLSPGG1: 1000 lines/mmG2: 600 lines/mm
4250040000
71910
2500
61338
73910 114000
61910
10955
955
75000
50000 60955
10000
0
Mh
179°side view
M3APPLE-2
M1 M2
S1 S2177° 176°174°
175°
Mv
M4ST1 ST2 ST3
u=12cm
N=16
0 10 20 30 5040 60 70 80 90 100 110 120 130 140
Distance to source point (m)
MhMv
variably-polarizing undulator
monochromator
biological application
station
beam-transport pipe
entrance slit
M1,M2
VLSPG
exit slit
M3 M4
RI inspection port 2
surface photo- chemistry station
fluore- scence screen
RI inspec- tion port 3
radiation detector
acitinide science station
beam monitor
cryopump system
fast closing gate valve
fast closing gate valve
fast closing gate valve
experimental hallHot Sample Area
hutch for optics
beam shutter
XYslit
absorber
front end
fixed mask
beam position monitor
RI inspection port 1
-stopper
XY slit
fluorescence screen
fluore- scence screen
u=12cm Np=16
(Hettrick-Underwood type)
200 500 1000 1500 2000
photon energy (eV)
174° G2
176° G2
176° G1
Y. Saitoh et al., Nucl. Instrum. Methods A ’01.
JAERI beamline BL23SU of Spring-8JAERI beamline BL23SU of Spring-8
Helical undulator VLS-PGM
Y. Saitoh et al., Rev. Sci. Instrum. ’ 00
JAERI beamline BL23SU of Spring-8JAERI beamline BL23SU of Spring-8
MCD装置
ARPES装置
ARPES endstation Scienta 2002 (Gammadata VUV5000)MCD endstation Superconducting magnet, up to 10 T Low temperature, down to ~10 KMeasurements of U compounds allowedIn situ PES of oxide thin films by PLD
Endstations at BL23SUEndstations at BL23SU
0 10 20 30 5040 60 70 80 90 100 110 120 130 140
Distance to source point (m)
MhMv
variably-polarizing undulator
monochromator
biological application
station
beam-transport pipe
entrance slit
M1,M2
VLSPG
exit slit
M3 M4
RI inspection port 2
surface photo- chemistry station
fluore- scence screen
RI inspec- tion port 3
radiation detector
acitinide science station
beam monitor
cryopump system
fast closing gate valve
fast closing gate valve
fast closing gate valve
experimental hallHot Sample Area
hutch for optics
beam shutter
XYslit
absorber
front end
fixed mask
beam position monitor
RI inspection port 1
-stopper
XY slit
fluorescence screen
fluore- scence screen
u=12cm Np=16
(Hettrick-Underwood type)
MCD
PES
Synchrotron Radiation
Advantages of soft x-ray photoemissionAdvantages of soft x-ray photoemission
• Longer mean-free path– More bulk-sensitive
• Larger d- and f-orbital (relative) cross-sections– Stronger resonant enhancement for some core levels
• Lower background
• Smaller uncertainty in kz
– ARPES of 3D materials
• Disadvantages– Lower energy (x 10) and momentum (x 7) resolution– Lower absolute cross-sections
Mea
n fr
ee p
ath
(Å)
Kinetic energy (eV)
Probing depth of photoelectronsProbing depth of photoelectrons
Laser
Dischargelamp
Soft x-rays
Hard x-rays
VUV
Synchrotron radiation
VIS-UV
h U 5f / Fe 3d U 5f / Ga 4p
800 eV 2.5 55.6
500 eV 1.5 49.7
400 eV 1.0 43.6
U 5f Fe 3d
Photon energy dependence of atomic orbitalPhoton energy dependence of atomic orbital cross-sections cross-sections
Photon energy dependence of atomic orbitalPhoton energy dependence of atomic orbital cross-sections cross-sections
S.I. Fujimori et al
Cross-section ratio
Lack of resonant photoemission at U 4Lack of resonant photoemission at U 4dd edge edgeLack of resonant photoemission at U 4Lack of resonant photoemission at U 4dd edge edge
724 eV
736 eV
normalized to photon flux
normalized to total area
S.I. Fujimori et alJ. W. Allen, J. Electron Spectrosc. ’96
Inte
nsi
ty (
arb
. u
nits
)
-15 -10 -5 0 5Energy relative to EF (eV)
La1-xSrxFeO3
x = 0
0.2
0.4
0.67
PESh = 600 eV
XAS
A (eg)
B (t2g)C
D
E
F
sat.
Hole-doping-induced changes in spectra of Hole-doping-induced changes in spectra of in situin situ-prepared La-prepared La1-x1-xSrSrxxFeOFeO3 3 thin films thin films
Bulk polycrystals Single-crystal films
H. Wadati et al., PRB, in press; cond-mat/04
A. Chainani et al., PRB ‘93
(t2g)
(eg)
@ Photon Factory BL2c
A1 - A2
Magnetic circular dichroism (MCD) in core-level Magnetic circular dichroism (MCD) in core-level x-ray absorption (XAS) from metal 2x-ray absorption (XAS) from metal 2pp core level core level
element specific probe
spin sum rule
orbital sum ruleMn 2p
Mn 3d
h
In situIn situ measurements of Ca measurements of Ca1-x1-xSrSrxxRuORuO33 thin films thin films
10μm□4μm□3~6unit /
1stepJ. Park et al. PRB ’04
K. Terai et al.
ex situ measurementsh = 52eV-100eV difference
Band calc.
Ferromagentic superconductor UGeFerromagentic superconductor UGe22
S. S. Saxena et al., Nature ‘00A. Huxley et al., PRB ‘01N. Tateiwa et al., JPSJ ‘01
ferromagnetic
supercond.
TCurie = 52 K TSC = 0.8 K@1.2 GPaT* ~ 30 K: anomaly ?
T*
T*
TCurie
new order parameter ?
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
42 K
36 K
33 K
30 K
25 K
U N4,5 XAS
N5N4
-0.15
-0.10
-0.05
0.00
840820800780760740720700
Photon Energy (eV)
U N4,5 MCD
42 K 36 K 33 K 30 K 25 K
1.0
0.8
0.6
0.4
0.2
0.0840800760720
T = 25 K
T. Okane et al.
U U NN4,54,5 (4 (4dd 5 5ff) MCD of UGe) MCD of UGe22
H. Ohldag et al., APL ‘00
x = 0.02T = 15 - 30 KH = 0.55 T
Previous core-level MCD studies of GaPrevious core-level MCD studies of Ga1-x1-xMnMnxxAs As
Y. L. Soo et al., PRB ‘03
D. J. Keavney et al., PRL ‘03
Mn 2p Mn 2p
As 2p3/2
Evidence for carrier-induced magnetism
H. Ohno et al., JMMM, ‘99
Curie temperature drops above x ~ 0.05
A. Oiwa et al., Solid State Commun. ’97
T = 2 K
x = 0.071
0.053
0.043
0.035
Indication of multiple Mn species in GIndication of multiple Mn species in Gaa1-x1-xMnMnxxAs As
Paramagnetic signals in magnetization curves above x ~ 0.05
Compensation of hole carriers by defects ?
S.J. Potashnik et al., APL (2001)
Change of TC by post annealing
Mn substituting Ga sites (MnGa): Mn3+ Mn2+ + holeMn at interstitial sites (MnI): Mn0 Mn2+ + electrons: compensates holes !
Interstitial Mn in GaInterstitial Mn in Ga1-x1-xMnMnxxAs ?As ?
Annealing converts MnI to MnGa ?
As Ga
S.C. Erwin and A.G. Petukhov PRL ‘02
First, Mn enters interstices then Ga site
Molecular dynamics simulation of MBE
F. Matsukura et al. PRB ‘98
x = 0.053
A. Oiwa et al., Solid State Commun. ’97
T = 2 K
High-field magnetization of GaHigh-field magnetization of Ga1-x1-xMnMnxxAs As
x = 0.071
0.053
0.043
0.035
s.i. GaAs(001)
GaMnAs
As cap
20 nm
1 nm
GaAs
Tc = 40 K
MCD intensity ~ 33 % 60% of Mn atoms are ferromagnetic
Mn 2Mn 2pp MCD spectra of Ga MCD spectra of Ga1-x1-xMnMnxxAs (x = 0.078) As (x = 0.078)
Y. Takeda et al.
Y. Ishiwata et al., PRB ‘02
Substitutional Mn Out-diffused Mn from interstitial sites
Fist-principles calc.In situ Auger, resistivity meas. K. W. Edmonds et al, PRL ‘04
Two signals in Mn 2Two signals in Mn 2pp XAS spectra of Ga XAS spectra of Ga1-x1-xMnMnxxAsAs
and LT-annealing effectand LT-annealing effect
Curie temperatures for Mn-doped Curie temperatures for Mn-doped pp-type semiconductors -type semiconductors
T. Dietl et al, Science (2000)
if hole-doped
Room-temperature ferromagnetism Room-temperature ferromagnetism in Znin Zn1-x1-xCoCoxxOO
M. Kobayashi et al.K. Ueda, H. Tabata, T. Kawai, APL. ‘01
magnetic impurities such as spinel ?
TC ~ 300 K !
but small moment
Magnetization
~5 % of total Co ions
-150
-100
-50
0
50
100
150
Mag
neti
zati
on x
10-6
(em
u)
-20 -10 0 10 20
Magnetic Field (kG)
@5K @300K
Mtotal = Mferro + Mpara + Mdia (substrate)
MCD of ferromagnetic component
MCD of paramagnetic component
• Basic sciences of correlated systems– Band structure of U, Ce compounds and correlation effect– Band structure of three-dimensional transition-metal oxides – Electron correlation in various types of interfaces
• Characterization and new physics in nano-materials– Identification of ferromagnetic states in DMS’s– Characterization of paramagnetic/defect states in DMS’s – Magnetism in interfaces, nano-structures, ….– Intercalation, nano-magnets, …..
• Possible future directions/development– Octapole magnet, ultra-low temperature (e.g., Elettra) – MCD-XES – truly bulk-sensitive magnetic properties
Conclusion - Scientific opportunities and Conclusion - Scientific opportunities and directions using SX-ARPES and MCD directions using SX-ARPES and MCD
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