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

Soft x-ray beamline BL2c of Photon FactorySoft x-ray beamline BL2c of Photon Factory

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

PLD

SR

PES

CCD Cameras

Combined Combined in situin situ PES-PLD system PES-PLD system

Nd:YAG laser

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