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HAXPES 2009
High Energy Photoemission of Heusler compounds
Claudia FelserMainz: G. H. Fecher, S. Ouardi, B. Balke, T. Graf, C. Blum, F. Casper, S. Chadov, A. Gloskowskii,SPring8: E. Ikenaga, S. Ueda, K. Kobayashi, Y. Yamashita, H. Yoshikawa,BESSY: M. Mertin, F. Schäfers, M. GorgoiHokkaido: T. Ishikawa, T. Uemura, M. Yamamoto,Munich: J. Minar, J. Braun, H. Ebert
HAXPES 2009
•
Concept
•
Design scheme for Heusler compounds
•
High energy photoemission of bulk materials
•
High energy photoemission of burried interfaces
•
High resolution and correlations
•
Summary
HAXPES 2009
Heusler Compounds as Multifunctional Materials•
Magnetic material: Cu2
MnAl•
Halfmetallic ferromagnet:
NiMnSb
•
Magneto-optical: PtMnSb•
Magneto-mechanic: Ni2
MnGa•
Superconductor: Pd2
YSn•
Semiconductors: CoTiSb
•
Heavy fermion: Fe2
VAl •
Li-conductor: LiMnSb
•
Magneto-electronic:
Co2
FeSi•
Thermo-electric: TiNiSn
•
Diluted Semiconductors CoTiSb:Fe•
Magneto-caloric: CoMnSb:Nb
19051983
2001
C. Felser, G. Fecher, B. Balke, Invited Review for Angewandte Chemie, Int. Ed. 46 668 (2007).
HAXPES 2009
TMR and GMR for applications
Sakuraba et al. APL 89 (2006) 052508
Sakuraba et al.
APL 88 (2006) 192508
TMR ratio = 67% at RT, 580% at 2K
Co2 MnSi
Co2 MnSiAl2 O3
Inomata et al. to be published
HAXPES 2009
R. Asahi et al. J. Phys.: Cond. Mat. 20 (2008) 64227K. Miyamoto et al. Appl. Phys. Express 1 (2008) 081901 E. Toberer, Nature Mat. 7 (2008) 105 VK Zaitsev et al. PRB 74 (2006) 045207
0 200 400 600 800 10000,00,20,40,60,81,01,21,41,61,8 Bi2(Te0.8Se0.2)3
CoSb3
(Zr0.5
Hf0.5
)0.5
Ti0.5
NiSn0.998
Sb0.002
Si0.8
Ge0.2
(Hf0.5Zr0.5)NiSn (OFZ) Mg2Si0.8Sn0.2
Figu
re o
f mer
it ZT
Temperature T K
C1b Heusler for Thermoelectrics
TZT 2
Typ M aterial Price in $/kg
(m etals) V-VI Bi 2Te3 14 0 IV -V I Pb Te 99 Zn 4Sb 3 Zn 4Sb 3 4
p -M n Si1.7 3 24 n -M g 2Si0.4Sn 0.6 18 Si0.80Ge0.20 66 0
Silicides
Si0.94Ge0.06 27 0 Skut te ru t ide s Co Sb 3 11 Half-Heusler TiNiSn 55 n/p-Clath rate Ba8Ga16Ge30 100 0
w i t h o u t Ba O xides p -NaCo 2O 4, 17
w i t h o u t Na, O Zin t l Phasen p -Yb 14M n Sb 11 92 Th 3P4 La3-XTe4 160
Kandpal et al. J. Phys. D 39 (2006) 776
HAXPES 2009
•
Concept
•
Design scheme for Heusler compounds
•
High energy photoemission of bulk materials
•
High energy photoemission of burried interfaces
•
High resolution and correlations
•
Summary
HAXPES 2009
Half-Heusler C1b
Structure
Rational Design
XYZ X2 YZ
Heusler L21ホイスラー
HAXPES 2009
Synthesis
Semiconducting Heuslers – Stuffed ZnS
XYZ X2 YZ
Ti
Si2
AsGa
Co Sb
9 + 4 + 5 = 18
3 + 5 = 8
CuLi2 Sb
VFe2 Al
2*8 + 5 + 3 = 24
2*1 + 11 + 5 = 18
additional t2
-levels
HAXPES 2009
Slater-Pauling Rule
Kübler 1983Galanakis et al., PRB 66, 012406 (2002)
Magic valence electron number X2
YZ 24Valence electrons =24 + sat. magnetization
Co2
FeAl2*9 + 8 + 3 = 29 Ms = 5B
B. Balke et al., Sci. Technol. Adv. Mater. 9 (2008) 014102.
EF
HAXPES 2009
•
Concept
•
Design scheme for Heusler compounds
•
High energy photoemission of bulk materials
•
High energy photoemission of burried interfaces
•
High resolution and correlations
•
Summary
HAXPES 2009
Sur
vey
on H
iTT
–Mat
eria
ls
C1b Heuslers: Tunable Band Structures
Kandpal et al. J. Phys. D 39 (2006) 776
−6 −4 −2 0 2 4 6energy (eV)
0
10
20
30
40 TiCoSbVCoSnNbCoSn
0
10
20
30
40
DO
S (
stat
es e
V−
1 cel
l−1 )
VFeSbTiCoSbYNiSb
(a)
(b)
CoTiSbNiTiSnNiYSbAuYSnAuYPb
•
Tunable gaps •
Easy to substitute
•
Cheap
HAXPES 2009
Thermoelectrica CoTiSb and Gap
-15 -10 -5 0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-2.0 -1.5 -1.0 -0.5 0.0 0.50.0
0.1
0.2
0.3
0.4
0.5
h = 5.9 keV
Nor
mal
ized
inte
nsity
Energy E - F [eV]
CoTiSb bulk @ 300K CoTiSb bulk @ 18K
-1,5 -1,0 -0,5 0,0
Nor
mal
ized
inte
nsity
Energy E - F [eV]
CoTiSb bulk @ 18K CoTiSb bulk @ 300K
−6 −4 −2 0 2 4 6energy (eV)
0
10
20
30
40 TiCoSbVCoSnNbCoSn
0
(b)
Nice agreement between theoretical and experimental gap: 1 eV gap
HAXPES 2009
Ball Milling of Thermoelectrica CoTiSb
10 20 30 400,0
0,4
0,8
SbCo
CoTiSb
rel.
inte
nsity
I/I 0
Co+Ti+Sb powder CoTiSb arc melting 13 h milling
Ti
Starting from elements after 13 h nearly the same XRDdifference in the valence band: broadening
-16 -14 -12 -10 -8 -6 -4 -2 00,0
0,2
0,4
0,6
0,8
1,0 Powder Bulk Au
Nor
mal
ized
inte
nsity
Energy E - F [eV]
XRDHigh Energy PES
Ouardi et al. in preparation
HAXPES 2009
Design of a Dilute Magnetic SemiconductorValence electrons
2 x 4 = 8
3 + 5 = 8 + x
Zinc-Blende C1b
9 + 4 + 5 = 18 ± xTi
Si
AsGa
Co Sb
Mn
Fe
HAXPES 2009
Sur
vey
on H
iTT
–Mat
eria
ls
Tunable properties of Half Heuslers
Balke et al. Phys. Rev. B
77, 045209 (2008)
CoTi0.95
M0.05
Sb
Number of Valence electroncs Easy to tune
•
ferromagnetic M = Fe, Mn, Cr•
paramagnetic M = V
•
diamagnetic M = Sc und Ti
-4 -2 0 2 4-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
-2 0 2-0.02
0.00
0.02
CoTi0.9Y0.1SbY =
Fe Mn Cr V
Mag
netic
mom
ent
m [
B]
Induction field 0H [T]
HAXPES 2009
High Energy PES of CoTi1-x Fex Sb
-14 -12 -10 -8 -6 -4 -2 0 20.0
0.2
0.4
0.6
0.8
1.0
Fe induced
Nor
mal
ised
inte
nsity
I /
I max
Energy E F [eV]
hv = 2.5 keV CoTi0.9Fe0.1Sb CoTiSb
HAXPES reveals the small changes in the density of states that are induced by the substitution by iron.
Balke et al. Phys. Rev. B 77 (2008) 045209Fecher et al. JESRP 156-158 (2007) 97
HAXPES 2009
•
Concept
•
Design scheme for Heusler compounds
•
High energy photoemission of bulk materials
•
High energy photoemission of buried interfaces
•
High resolution and correlations
•
Summary
HAXPES 2009
High Energy PES of buried films
Fecher et al. APL 92 195313 (2008)Ouardi et al. J. Phys. D 42 084010
(2009)
MgOsubstrate
50 nm Co2 MnSi
1nm AlOx
MgO2nm, 20nm
HAXPES 2009
Film quality studied by High Energy PES1nm AlOx
h
= 7.94 keV
-14 -12 -10 -8 -6 -4 -2 00.0
0.2
0.4
0.6
0.8
1.0
1.2
as-grown annealed Bulk
Mn t2g
Co t2g Mn eg
Si a1g
Rel
ativ
e in
tens
ity
Energy E F (eV)
MgOsubstrate
30 nm Co2 MnSi
1nm AlOx
MgO2nm
Irradiation improves the film quality
O. Gaier et al. APL 94 152508 (2009)
HAXPES 2009
•
Concept
•
Design scheme for Heusler compounds
•
High energy photoemission of bulk materials
•
High energy photoemission of buried interfaces
•
High resolution and correlations
•
Summary
HAXPES 2009Problem with Co2 FeSi
TheoryFull Potential GGA
LSDA does not reflect the correct
electronic structure of Co2
FeSi
W L X W K W L X W K10 5 0 5 10
Density of states [eV-1]
-12-10-8-6-4-20246
minority
Ener
gy
E F [e
V]
Momentum k
majority
Momentum k
Experiment: mexp = 6 B
Calculation: mcalc = 5.59 B
Wurmehl, et al ., APL 88 (2006) 032502.Wurmehl, et al ., Phys. Rev. B 72 (2005) 184434
HAXPES 2009Minority gap in Co2 Mn1-x Fex Si
●
UCo
= 1.9 eV●
UMn
= 1.77 eV●
UFe
= 1.785 eV
LDA + EXX
0.00 0.25 0.50 0.75 1.00-1.0
-0.5
F
0.5
1.0
1.5
HMF
HFM ?
Co2Mn(1-x)FexSi
LDA + EXX
LDA + U CB VB
Band
gap
ene
rgie
s E
[eV
]
Fe concetration x
HMFFM
Kandpal et al., PRB
73 (2006) 094422Chadov et al. J. Phys. D 42 084002
(2009)
0
0.05
0.1
0.15
0.2
-12 -10 -8 -6 -4 -2 0E-E
F (eV)
0
0.05
0.1
0.15
0.2
LSDA
LSDA+U
Wien2k: Tran et al., PRB 74 2006 155108
KKR: Ködderitzsch et al. PRB 77 2008 045101
Exc(EXX, F-) = Exc(LDA) + {Ex(HF) -
Ex(LDA)}
Co2 MnSi
HAXPES 2009Co2 Fe1-x Mnx Si
0 20 40 60 80 100concentration of Fe (%)
5
5.2
5.4
5.6
5.8
6
μ tot (
μ B)
ExperimentLSDALSDA+ULSDA+U+DMFT
Chadov et al. J. Phys. D 42 084002
(2009)
HAXPES 2009Summary
HAXPES is a new tool to investigate the bulk properties of spintronics and thermelectric materials
HAXPES of thin films can help to improve the film quality
HAXPES of the valence band of tunnel junctions
To describe the electronic structure of Heusler compounds (L21
) correlations have to taken into account
SPINHAXPES and MCD will help to determine the spin polarization (with Claessen, Drube, Schoenhense, Kobayashi …)
HAXPES 2009Co-workers
Spring 8: Keisuke Kobayashi, Eiji Ikenaga, Jung-Jin Kim, Yuji Saitoh , Yukiharu Takeda , Shigenori Ueda, Yoshiyuki Yamashita, Hideki Yoshikawa, Ke Yang. JST-DFG
NIMS: K. Inomata et al. JST-DFG
Sapporo: M. Yamamoto JST-DFG
Sendai: Y. Ando et al. FG559
LMU: H. Ebert, J. Minar, J. Braun
BESSY, Berlin: Wolfgang Eberhardt, Marcel Mertin, Franz Schäfers, M. Gorgoi.
SPECS, Berlin: Sven Mähl, Oliver Schaff.
DFG-FG559, FE633, SP1166, BMBF: HAXPES, HEUSPIN, MULTIMAG
HAXPES 2009High Curie Temperatures
Fecher, J. Appl. Phys. 99 (2006) 08J106Kübler et al., Phys. Rev. B 76 (2007) 024414
Expected Curie temperature for Co2 FeSi : > 1000K
HAXPES 2009
Co2 FeSi
Magnetic moment in saturation: 5.97B
0.1B at 5K
Extrapolation to 0K :Slater-Pauling rule: 6 B
Curie Temperature 1120 K
-3 -2 -1 0 1 2 3
-6
-4
-2
0
2
4
6
-2.0k 0.0 2.0k-1.0%
-0.5%
0.0%
0.5%
1.0%
5K 300K 775K
Mag
netic
Mom
ent p
er u
nit c
ell
m [
B]
Magnetic Field H [106 A/m]
Wurmehl, et al ., APL 88 (2006) 032502
.Wurmehl, et al ., Phys. Rev. B
72 (2005) 184434
700 800 900 1000 1100 1200 13000
10
20
30
40
50
60
TC
1/(T) = 1150 ± 50 K
(T)TC = 1100 ± 20 K
0H = 0.1Tm = 47 g
Spec
ific
Mag
netiz
atio
n
[Am
2 kg-1]
Temperature T [K]
0
200
400
600
800
Inve
rse
Susc
eptib
ility
120 140 160 180
6 8 10 12 14 16 18 20 22 24 26 28
Hyperfeinfeld (T)
59C
o S
pin-
Ech
o In
tens
ity (a
rb. u
nits
)
Frequency (MHz)
HAXPES 2009
HAXPES 2009Valenceband
7937 7938 7939 79400,0
2,0x10-1
4,0x10-1
6,0x10-1
8,0x10-1
1,0x100
VBHR-RTTa =
520 K 620 K 770 K 920 K
Inte
nsity
Kinetic energy Ekin [eV]
7937 7938 7939 79400,0
2,0x10-1
4,0x10-1
6,0x10-1
8,0x10-1
1,0x100VBHR-LT Ta =
520 K 620 K 770 K 920 K
Inte
nsity
Kinetic energy Ekin [eV]
HAXPES 2009
HAXPES of CIS
-8 -6 -4 -2 0
CIS CIS and CdS
Inte
nsity
a.u
.
Binding Energy (eV)
-8 -6 -4 -2 00
5
10 CuInSe2c/a=2.01
stat
es/e
V
Energy (eV)
Total Cu-tot Cu-d In-tot In-p Se-tot Se-p
h
= 8 keV Cross sectionMainly s and p states
HAXPES 2009HAXPES: CIS
-10 -8 -6 -4 -2 0
Inte
nsity
, a.u
.
Binding Energy, eV
CIGS_VB_2.2keV CIGS_VB_3keV CIGS_VB_4keV CIGS_VB_5keV CIGS_VB_8keV
Bandgap about 0.8 eVCu 3d
-8 -6 -4 -2 00
5
10
15 CuInSe2c/a=2.01
stat
es/e
V
Energy (eV)
Total Cu-tot Cu-d In-tot In-p Se-tot Se-p
h
= 2 keV –
8 keVIntensity depends on Cross sections !
HAXPES 2009
HAXPES of CIS +/- CdS
-8 -6 -4 -2 00
2
4
6
8
10
stat
es/e
v
Energy(eV)
Total Cd-tot Cd-s Cd-d S-tot S-s S-p
-8 -6 -4 -2 00
5
10 CuInSe2c/a=2.01
stat
es/e
V
Energy (eV)
Total Cu-tot Cu-d In-tot In-p Se-tot Se-p
-10 -8 -6 -4 -2 0
Inte
nsity
a.u
.
Binding Energy (eV)
CIS CIS and CdS
