広大放射光を用いた磁性体の分光研究 Hiroshima Synchrotron

!"#$%&'()*+,-./01!2345-46789
:::::::::;<<=>?<@?ABCDEFGH"<<;IJKL
Hiroshima Synchrotron Radiation Center
http://www.hsrc.hiroshima-u.ac.jp/
BL-9A: High resolution ARPES with low h!
photons
(h!=4-40eV)
XYZ[.\]^_/*5>-.`a
XgYhdih`ajkijhlm
BL-14: Core absorption linear and
circular dichroismd+h!=100-1200eV,
BL-9B: Spin polarized photoelectron
spectroscopyd(h!=16-300eV)
bcdef
BL-7; Photoelectron spectroscopy of Solids
+h!=30-380eV,
BL-1: High resolution ARPES with VUV
photons +h!=26-300eV,
Ouiline
!"#$%&'()*+XMCD, XLD,-.
&fcc Fe/Cu/*01
HiSOR BL-14DEFG!"#$-.HI
HiSOR BL-14 (BM)
&2/*Mott345 YTiO3
6789:;2/*<=>.?@-.
&Co2MnGe
&NiMnSb
&Ru2-xFexCrSi
8AB!C-".?@-.
&fcc Co ultrathin film/Cu
#$-.
!"#$%&'
JKLM*
NOP#QRSTUVW
XMCD
XLD
X-ray magnetic circular dichroism
Linear dichroism of YTiO3
Cr/ fcc Fe
Properties
YTiO3 (d1 system)
· Mott-Hubbard type insulator
(d)
(d)
· Ferromagnet ( TC = 30K )
eg
xy
t2g
yz zx
nopqr
!
Jahn-Teller distortion
K. Yaji, in prep.
Linear dichroism of YTiO3
! !
Linear dichroism of YTiO3
3
YTiO3 T=300K
10
-4
Orbital ordering
GdFeO3-type structure
0
Ti L23 XAS & XLD spectra
"+ = c1 zx + c 2 yz
a-plane
-6
!
!
!
Antiferro-orbital ordering is responsible
for the ferromagnetism.
• Polarized neutron diffraction (PND). c1 ~ 0.6
(J. Akimitsu et al., J. Phys. Soc. Jpn. 70 (2001) 3475.)
c1 ~ 0.7
• Resonant X-ray scattering (RXS).
! (2002) 184419.)
(H. Nakao et al., Phys. Rev. B 66
c1 ~ 0.8
• NMR
(M. Itoh et al., J. Phys. Soc. Jpn.
!68 (1999) 2783.)
!
10
-4
(d)
0
-4
calc. Fc - Fa
(c1=0.8)
b-plane
exp.
Fc - Fa
exp.
-{(Fb - Fc)+(Fa - Fb)}
-2
(b)
6
c-plane
3
exp. Fa - Fb
calc. Fa - Fb
(c1=0.8)
-4
(d)
(a)
2
10
Normalized Intensity of XLD ( x 10
-4
)
"# = c1 zx # c 2 yz
"#!
"+
exp. Fb - Fc
calc. Fb - Fc
(c1=0.8)
-3
0
Orbital ordering pattern in YTiO3.
(c1~0.7)
-3
F. Iga et al., Phys. Rev. Lett. 93 (2004) 257207.
Fig.4
(c)
460
470
480
Photon Energy ( eV )
F. Iga et al.
s5>.?@-.
Linear dichroism of YTiO3
.?@-.>yi
F. Iga et al., Phys. Rev. Lett. 93 (2004) 257207.
Integrated XLD intensities
exp.
c1 = 0.9
c1 = 0.8
c1 = 0.7
c1 = 0.6
a-plane
(Ib – Ic) / I
–0.0271
–0.01474
–0.02036
–0.02903
–0.03675
b-plane
(Ic – Ia) / I
–0.00556
–0.00769
–0.00100
+0.01011
+0.02100
c-plane
(Ia – Ib) / I
+0.0261
+0.02243
+0.02136
+0.01892
+0.01573
{(Ib–Ic)+(Ic–Ia)+(Ia–Ib)}/I
–0.0066
0
0
0
0
(Ib – Ic) /(Ia – Ib)
–1.038
–0.365
–0.95
–1.53
–2.33
(Ic – Ia) /(Ia – Ib)
–0.213
–0.635
–0.05
+0.534
+1.333
(d)
"± = 0.8 zx ± 0.6 yz well explains the observed data.
Consistent with NMR result.
EF : z{O|}~
EV : $•}~
EB : ۥtuOv:
EK : .?@>‚ƒtuOv:
tuOv:„…†
h" = E B + ! + E K
!
s5>.?@-.
‡ˆ.?@-.>yi
s5>.?@-.
• Multi-channel detection
• High angular resolution < 0.1°
• High energy resolution < 5meV
‰Š>.?@Z‹Œ•
‡ˆ.?@Z‹Œ•
.?@tuOv:-wx
Electron inelastic mean free path (IMFP)
VUVŽ•.
Properties of Co2MnGe
HXŽ•.
Properties
&L21 structure (a~5.74Å)
&Very high Curie temperature
TC~905K
&Large magnetization
M ~ 5 µB/unit cell
Co2MnGe
Half metallic energy band structure first predicted by S.Fujii and S.Ishida et al.
JKLM
S. Fujii, S. Sugimura, S. Ishida and S. Asano,
J. Phys.: Condens. Matter 43 (1990) 8583.
NOPLM
Possible applications to spintronics devices!!
Spin injection into semiconductor with high spin pol.
TMR device with huge MR ratio..
JK–NOP>?@—˜\-™š&“›œ
Only a few reports on the experimental study of the electronic structure.
Photoelectron spectra with hard X-ray
Photoionization cross section
SPring-8 BL-22/29XU(HX)
HXŽ•.
Ge4s/Co3d~0.01
Ge4s/Mn3d~0.02
8keV
”400•
&T=40K
K. Miyamoto et al.
&Resolutions: 350/250meV
Bulk sensitivity has improved.
Ge 4s&4p bands are emphasized.
Ionization cross section:
Ge4s/Co3d~4
Ge4s/Mn3d~10
VUVŽ•.
Co&Mn3d NB•‘’%D&“
3.5keV
4s&4p NB•‘’%D&“
Ge 4s /Co3d~ 4
Ge 4s /Mn3d~10
@3.5keV
Overall agreement between the experimental and
theoretical DOS.
The observed photoelectron structures are consistent
with the calculated DOS except for the energy shift of
the peaks toward higher EB.
¼š^«8AB¸¹½Q Ru2-xFexCrSi
Ru0.5Fe1.5CrSi : Valence band PES spectra
k)*' : ¢£,¤¥ ¦(§¨gYh)
majority
¾¿6789:(L21);<=Ru2-xFexCrSi
/©M~2µB/formula unit
Ru0.5Fe1.5CrSi
Ru4d
Ru4d
B
C
minority
Tc ~ 460K
EF ¡>—˜ªC‘«^
¬-®>¯°y@±²>³(†
Ru4d/Fe3d
~0.01
Ru0.5Fe1.5CrSi
valence band
Fe3d, Cr3d
A
h!=
3500eV
¬-ÀÁ,k*“ : Ã¥,XÄ ¦(§¨gYh)
Ru2-xFexCrSi
‘´µ¶·«^8AB¸¹C\º»
Ru4d/Fe3d
~2
690eV
490eV
¼š^«8AB¸¹½Q
–š¶ÅÆ
100eV
K. Sakamoto et al.
K.Matsuda.et.al., J.Phys.:Condens.Matter.17.5889(2005)
HI&NB•'•(³(†+)–>žŸ
HI&NB•'•–>žŸ
- experiment
h!=3500eV
NB•'•R¢£,¤¥ ¦+§¨gYh,
- band calc
NB•'•R¢£, ¤¥ ¦+§¨gYh,
³(†+
h!=3500eV
: experiment
: Ru4d
: Fe3d
: Cr3d
: Si3p
h!=690eV
Ru2-xFexCrSi
Ru2-x(Fex-yCry)(Cr1-yFey)Si (Fe-Cr disorder)
y=0.125
y=0.25
h!=3500eV
- experiment
- band calc
h!=490eV
h!=100eV
EF ¡
: Fe3d, Cr3d
A (EB~2eV)
: Fe3d
B,C (EB=4~8eV) : Ru4d
EF
¡>2C=Y
EF
disorder:y >ÇÈ
¡>2C=É
Schematic Figure of Mott Scattering
Spin Polarized Photoelectron Spectroscopy
Photoelectron intensity v.s. Electron kinetic energy
• Spin-orbit interaction
Energy conservation
VLS =
h" = EB + ! + Ekin
Ze 2
v v
(s " l )
2 2 3
2m c r
• Experimental Asymmetry
Spin polarization
P=
!
A=
N" # N!
NL " NR
= Seff # P
NL + NR
• Efficiency
N" + N!
!
I
" = # Seff2
I0
"10-4
low efficiency#large photon flux
!
Purpose of this work
Spin resolved photoemission experiment
with recently developed spin detector
Top view
We chose magnetic thin film of Co/Cu(001) as a first example
r
M
sample
Pass energy = 5eV
for a test measurement to check the reliability of our SARPES system.
40º
The other reasons for this experiment,
1. For Co/Cu, it is easy to control the film thickness.
2. In-plane easy magnetization axis, suitable for our system.
3. A magnetic dichroism of spin-resolved valence band
photoemission spectra could be quite useful.
Un-polarized light
[110] [1 1 0]
!
Hemispherical electron analyzer:
(OMICRON EA125)
Angular resolution = ±1˚
Total energy resolution 110meV
e!
100mm !
Film growth of Co on Cu(001)
He discharge lamp
(Gammadata Scienta VUV5000)
Angle scanned along
Base pressure: 1.2x10-8 Pa
E-beam evaporation
AES and RHEED oscillation was used
for thickness determination
!
[1 1 0]
SARPES spectra of 6.5ML Co/Cu(001)
K. Miyamoto et al.
Clean and contaminated SARPES spectra
for normal emission
K. Miyamoto et al.
This state disappears upon 0.1 L O2 adsorption.
47º
42º
47º
47º
37º X
42º
42º
32º
37º X
37º X
!
32º
28º
!
32º
20º
28º
28º
12º
20º
20º
$=0º "
12º
12º
$=0º "
$=0º "
!
$=0º
Surface resonance d state
has been observed.
!
Future plan
Summary
()*+,-./0123456)74#$84
Soft X-ray (hv: 500-1000eV)
NOP>?@—˜
"E # 100 $ 300 meV
Hard X-ray (hv: 3.5-10keV)
VUV (hv: 20-100eV)
¡>?@—˜
"E < 10 meV
Ê:zËÌO*ÒØ>8ABDÙ…š_?@—˜\-Ú&“
8AB!C-".?@-.
+SARPES @HiSOR,
with VUV and low energy photon!
JK
!
Ê:zËÌO+–ÍÎÏÐG,6789:;2/*<=
&NiMnSb ! &Ru2-xFexCrSi
Low energy photon (hv<10eV)
EF
Contaminated
!
!
&Co2MnGe
Clean
NOP>?@—˜
¡>,ÑÒ?@ÓÔUz{O|ÕÖ×:
!
"E < 5 meV
&JKRÞKEßàNOP?@ÓÔ>-™
&8AB-"z{O|ÕÖ×:
1. Co2MnSi, Co2MnGe, NiMnSb,
Ru2-xFexCrSiÒØ>Û¬2. Û¬-01\ÜÁ
(Ý.R MgO UGaAs)
8AB-".?@-.
‡á`aâ
‡á`aâ
& HiSOR BL7 & 14Z[.):*97B
XgYhYhãih`aj
&YTiO3
äå.æçUèéêëUìíîïU£ðñò
XgYhZ[.jh`aóBÌ:
XgYhYhãih`aj
þÿ!"U#$"åU%$&eUÁ¥'(£ðñò
XgYhZ[.jh`aóBÌ:
& i`/Spring-8
& y`/Spring-8
CDæçUEcFòUG¥ñHUþIýJU«KLçU
H. B. HuangU¥®¼, LMN
ôõö÷Uø¥ùúUûü/úý
& 8AB&!C-".?@-.+,
XgYhYhãB2k)jh`aj
&Co2MnGe
O<PQjhYhdR£Sæ
&NiMnSb
TUhãYhd§Vdõ
-d.U/£0&1Ug¥02Uûü/úý
3Ü0åU1í4†U56Y7U¤0î2
MNOPQRSTUQVMWX
&JASRI/Spring-8 É8ñ’U9:;(Uä<=>UÉ?@A
&Ru2-xFexCrSi §¨gYhdÃ¥&WUXÄXYU0ìXZ
dddddddd ¢£d[U¤¥'å
XgYhYhãih`aj
äå.æç(D3) &fcc Fe/Cu/*01
h\]^`a_
XgYhYhãih`aj
#$"å(D1)
&fcc Co/Cu, Co2MnGe
XgYhYhãih`aj
%$&e (M2)
&Ru2-xFexCrSi, NiMnSb