Spectroscopic study of transition metal compounds

X-ray Photoelectron Spectroscopy (XPS)
and Magnetism
• Part I
Introduction
Experimental
Principles of XPS and SRPES
Selected results (intermetallic, organometallic,
spinels)
• Part II
Investigation of oxidic CMR compounds by XPS
and complementary techniques
Introduction
Abbreviations:
PES
Photoelectron Spectroscopy
XPS
X-ray (excited) PES
ESCA
Electron Spectroscopy for Chemical Analysis
SRPES
Spin-resolved Photoelectron Spectroscopy
UPS
Ultraviolet (excited) PES
ARUPS
Angle Resolved UPS
XES
X-ray (Photon) Emission Spectroscopy
XAS X-ray Absorption Spectroscopy
XMCD
X-ray magnetic circular dichroism
XMLD
X-ray magnetic linear dichroism
Investigation of all kind of materials:
metals, oxides, organo-metallic systems
(not shown: thin films, polymers, adsorbates,,,)
surface sensitive technique (electron escape depth)
XPS
• XPS is a very universal useful technique:
–
–
–
–
–
–
–
detection of almost all elements
core levels and valence bands are detected
determination of absolute atomic concentrations
valence state of ions deduced from chemical shifts (ESCA),
exchange interaction of the core hole with valence band
total DOS by XPS (and partial DOS by XES)
Spin resolved PES using circular polarized light or spin
detectors
Photo effect
hν = Ekin – Ebin
Evac = 0
one electron type picture
electron mean free path
Experimental
Light sources:
XPS: Al Kα radiation (1486.7 eV), also monochromatised
Synchrotron radiation with tunable energy
Electron detector:
High energy resolution, multi-channel,
spin resolving
Sample preparation:
in situ (UHV)
fracturing, evaporation,,,, no sputtering!
XPS
XPS
XPS
small spot anlysis
Excitation process
photo electron
XPS
Auger electron
AES
vacuum level
fluorescence
photon
XES
core level
XPS analysis
Ebin = hν - Ekin
XPS and AES lines can be identified by varying the excitation energy
XPS analysis
almost all elements are detectable, also quantitatively (sensitivity factors),
determination of absolute atomic concentrations, and stoichiometries,
2p1/2 and 2p3/2 (LS coupling), 6eV satellite
chemical shift
chemical shift
XPS: Mo 3d
Intensity (arb. units)
Sr2FeMoO6
reference compounds
Mo6+ in MoO3
Mo4+ in MoO2
the Mo 3d states are split
due to LS-coupling
MoO3
MoO2
240
Mo6+ and Mo5+ ions
in Sr2FeMoO6
235
230
Binding Energy (eV)
225
exchange splitting
1s XPS spectra of paramagnetic molecules
show a splitting due to the interaction
of the 1s hole with the spin S of the „valence band“
XPS probes the final states with S ± 1/2
3s splitting and
charge transfer (CT)
in 3d transition metal oxides
Interaction of the 3s hole with the 3d
electrons with spin S
XPS probes the final state S ± ½
in well screened systems charge is
transferred from O2p to 3d states
plus spin-spin interactions
A, B with charge transfer (CT)
C, D without CT (less screening)
3s splitting in TM oxides
valence band
tDos and pDos
Co2MnSn
(Heusler alloy)
tDos (total densities of states)
probed by XPS
pDos (partial densities of states)
probed by XES
comparison with theory
spin resolved
small gap?
Detection of Spin Polarization
Mini Mottdetector (SPECS)
SPLEED detector (Omikron)
Kirschner et al.
LEED ANALYZER
Detection of Spin Polarization
A design to detect
all three spin components
together with the
unpolarised signal.
D.J.Huang, P.D. Johnson, et al.
Rev.Sci.Instr. 73, 3778 (2002)
Spin resolved Photoelectronspectroscopy
Dietz
Alvarado, Campagna and Hopster
Dietz and Kuhlenbeck (1984)
Campagna 1985
SRPES from Fe 3s
HS
LS
HS: 2 Sz components
LS: 1 Sz component
D.J. Huang et al. Rev.Sci.Instr.73,
3778 (2002)
Earlier work by:
F.U. Hillebrecht, et al.
PRL65, 2450 (1990)
Z. Xu, et al.PRB51, 7912 (1995)
SRPES with cicularly polarized light
from nonmagnetic metals
total intensities:
I(f5/2) : I(f7/2) = 3 : 4
highly spinpolarized
D.J. Huang et al. Rev.Sci.Instr.73, 3778 (2002)
SRPES with circularly polarized light
Determination of the orbital moment
of CoO using spin-resolved photoemission
Highlights ESRF 2000
G. Ghiringhelli et al.
The orbital moment is quenched
also above TN !
Selected materials investigated by XPS
all kind of materials have been investigated by XPS,
only a few examples will be shown in the following:
intermetallic compounds (Heusler alloys)
chalcogenide spinels (partly semiconducting)
organometallic compounds
(molecule based solids and magnetic molecules)
oxides (CMR compounds: manganites, double perovskites)
Heusler-Alloys
•
•
•
•
•
•
discovered 1903 by F. Heusler
ternary intermetallic alloy:
X2YZ
L21 structure
4 interpenetrating fcc-lattices
here investigated: X2MnZ
– X = Fe,Co,Ni,Cu
– Z = Al,Si,Ga,In,Sn,Sb
partly HMF-behavior
– spin up: metal
– spin down: insulator /
semiconductor
Disorder in the Co/Mn sites
can close the gap and also
reduce the spin polarization.
Heusler-Alloys
X2MnZ
•
•
•
•
local magnetic moment at
the Mn-atom
2,3µB - 4,4 µB
Mn3d Ç : delocalised band;
hybridisation with the X 3d electrons
Mn3d È : localised unoccupied
states
magnetic coupling by the Z element
L21 Heusler-Alloys with Mn or Cr
Fe2MnZ
Co2MnZ
semi-Heusler
A2CrAl
Mn2p 3/2
Mn2p core levels
CoMn2p
2MnZ
Intensität (bel.Einheiten)
1/2
Fe 2 MnAl
Fe 2 MnSi
Co 2 MnAl
Co 2 MnGa
Co 2 MnSn
Co 2 MnSb
660
655
650
645
640
Bindungsenergie (eV)
635
630
∆ E (eV)
Mn2p3/2 splitting vs. µMn
1,8
1,7
1,6
1,5
1,4
1,3
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0,0
-1,0
Ni MnSb
Co 2 MnSb
Experiment
Co 2 MnSn
Co 2 MnGa
Theory
Co 2 MnAl
Ni 2 MnSn
Pd 2 MnSn
Rh 2 Mn Sn
Cu 2 Mn Al
Fe 2 MnAl
Co 2 MnSn
Ni 2 MnSb
Fe 2 MnSi
-0,5
0,0
0,5
1,0
1,5
2,0
µ Mn ( µ B )
2,5
3,0
3,5
4 ,0
4,5
Mn 2p photoelectron spectra
A comparison with atomic spectra
demonstrates the localized nature
of the Mn 2p states in MnO
multiplet effects need to be included
in calculations
Local moments also in Heuslers!
Ph. Wernet et. al.
Phys. Rev. B (2001)
chalkogenide spinels
Fe1-xCuxCr2S4
S
Fe2+Cr3+2S2-4
CuCr2S4 : Lotgering : Cu1+ (Cr3+, Cr4+)
Goodenough : Cu2+ (Cr3+)
Fe
Fe0.5Cu0.5Cr2S4:
Cr
Fe3+ / Cr4+ / S-
Ramirez et al., Nature, 386, 156 (1997)
x= 0
Chalkogenide spinels
prepared by
V. Tsurkan (Kishinau)
Cu1+
x= 0.5
FeCr2S4
Fe0.5Cu0.5Cr2S4
Cu 3d
S 3p
Fe 3d
S 3p
S 3s
Cr 3d
Intensity (arb. units)
Intensity (arb. units)
S 3s
Fe Lα
Cr Lα
Fe 3d
Cr 3d
Fe Lα
Cr Lα
S Kβ
Cu Lα
S L2,3
S Kβ
S L2,3
J. Phys.: Condens. Matter 12,
5411 – 5421 (2000)
15
10
5
Binding energy (eV)
0
- the VB states below EF are dominated by Cr 3d;
- minority-spin Fe 3d states produce a clear Fermi step in spectrum;
- the Fe 3d states are more localized than Cr 3d states;
- the Fe 3d and S 3p states are represented at slightly higher EB .
15
10
5
0
Binding energy (eV)
• contribution from the Cu
3d states just below Cr 3d.
Cu 2p & 3s XPS spectra
Cu 2p3/2
Cu 2p1/2
• no satellite in the Cu 2p spectra of Fe0.5Cu0.5Cr2S4
• no exchange splitting for the Cu 3s state
Cu2O
*
(1+)
Cu
Cu
FeO2
(2+)
O
110
970
Cu 3s
Intensity (arb. units)
Intensity (arb. units)
Fe0.5Cu0.5Cr2S4
960
950
940
930
115
120
125
130
135
Binding energy (eV)
Binding energy (eV)
⇒ 3d10 configuration of the Cu+ ion
Fe 2p & S 2p XPS spectra
Fe 2p1/2
Fe0.5Cu0.5Cr2S4 polycrystal
Fe0.5Cu0.5Cr2S4 *
FeCr2S4
Fe 2p3/2
Intensity (arb. units)
*
S 2p3/2
Additional features in the
polycrystal‘ spectrum
Ø wrong interpretation of
the experimental data !
2+
Fe Cr2S4
The importance of using
single crystals !!!
3+
2
Fe O3
168
738
732
S 2p1/2
726
720
714
708
Binding energy (eV)
charge transfer from S2- to Fe3+ : Fe2+
164
160
Binding energy (eV)
CuCr2Se4
PRB 59 (1999) 14552
Cu 2p3/2
F e 0.5 C u 0.5 C r 2 S 4
Intensity (arb.units)
Intensity (arb. units)
CuCr2Se4
C u 3s
Cu 2p1/2
Cr LMM
C uC r 2 S e 4
126
122
120
118
B inding energy (eV )
Se 4p Cu 3d
Intensity (arb. units)
124
970
960
950
Binding energy (eV)
Cr 3d
No exchange splitting of Cu 3s
⇒ Cu+ character of the Cu ions
10
8
6
4
2
Binding energy (eV)
0
940
-2
930
TM 3s splitting
Sol. St. Comm. 114 (2000) 149
FeCr2S4
Cr 3s
Fe 3s
Intensity (arb. units)
∆Eex(Fe) = 5.4 eV
Fe2+
Cr 3s
MnCr2S4
Mn 3s
∆Eex(Mn) = 5.7 eV
70
80
90
100
Binding energy (eV)
110
• the same Cr 3s exchange splitting ∆Eex (~ 4 eV) for all compounds
similar values for the local magnetic moments of Cr Cr 3+ ions
Mn2+
Cr 2p XPS spectra
ACr2S4 (A= Zn, Mn, Cd, Fe, Fe :Cu)
BCr2Se4 (B = Cd, Hg, Hg: Cu, Cu)
Cr 2p3/2
Cr 2p3/2
Cr 2p1/2
Intensity (arb.units)
Intensity (arb.units)
Cr 2p1/2
(e)
(d)
(c)
(d)
(c)
(b)
(b)
(a)
(a)
570
Eur. J. B 15 (2000) 401
575
580
585
Binding energy (eV)
590
570
575
580
585
590
Binding energy (eV)
µloc (Cr)= 2.9 - 3.0 µB → ∆E(Cr 2p)= 0.95-1.0 eV
→ localised character of the magnetic moments for Cr3+ in a 3d3 configuration.
Summary: chalkogenide spinels
•
CuCr2Se4 : monovalent Cu ions = Lotgering model
• Fe0.5Cu0.5Cr2S4 : Cu1+ mainly affects the Fe and S ions
• well-resolved Cr 2p splitting for Cr-chalcogenide spinels
• ACr2X4 : the same Cr 3s splitting = Cr3+ (3d3)
• XPS & XES data -- excellent agreement with band structure
calculations
organometallic materials
XPS on organometallic materials
ferric wheel
Magnetic molecules
Synthesized by R.Saalfrank et al.
Erlangen
di-cyanamides
molecule based solids
ferric star
Dicyanamide materials M[N(CN)2]2
M = Mn, Fe, Ni, Cu
• each metal ion is surrounded by
six nitrogen atoms in a distorted
(axially elongated) octahedral
geometry
M
N(1)
• the rutile-like structure consists
of rhombus-shaped units which
adopt a chain alignment parallel
to the c axis
C
N(2)
M
• tilting of the elongated octahedra
in the crystallographic ab plane
M = Mn,
Fe,
Co,
change over
Ni,
Cu
Dicyanamide materials M[N(CN)2]2
M = Mn, Fe, Ni, Cu
Crystallographic data - isostructural series
M
N(1)
C
N(2)
M
unit cell
change over
C.R. Kmety et al.
Physical Review B, 62 5576-5588 (2000)
Dicyanamide Mn[N(CN)2]2
3s splitting
J‘‘ dominant super exchange path
Magnetic moments on Mn:
4.65 µB/atom Mn[N(CN)2]2
4.45-4.79 µB/atom MnO
• the magnetic moment per Mn atom
is slightly reduced as expected from a
Mn2+ (3d5) ion due to a reduction
in spin polarization driven by
Mn(3d) Ù N(2sp) interaction.
Dicyanamides transition metal 2p core level spectra
Screening effects:
low with Mn and Fe
pronounced with Ni and Cu
valencies confirmed
as before
Valence bands of Mn[N(CN)2]2
N DOS
N 2p DOS
C DOS
C 2p DOS
Mn DOS
Mn 3d DOS
Phys. Rev. B66, 014446(8) (2002)
HOMO: Mn : majority spin
LUMO :
minority spin
filling of eg and t2g levels is important
for the super exchange interaction, and
responsible for the change over AFM - FM
D.O.Demchenko et al. Phys. Rev. B 69, 205105(9) (2004)
ferric wheel
[Li⊂Fe6L6]Cl*6CHCl3, L=N(CH2CH2O)3
prepared by Saalfrank et al. Erlangen
Valence bands ferric wheel
O2s
Fe 3d +O 2p
N2s
N, C2p
C2s
[Li⊂Fe6L6]Cl*6CHCl3, L=N(CH2CH2O)3
Determination of the valency of Fe
Fe2+L and Fe3+
S.G. Chiuzbaian et al. Surf. Sci. 482-485, 1272 – 1276 (2001)
A.V. Postnikov et al. J. Phys. Chem. Solids 65/4, 813-817 (2004)
ferric star
Fe-star
molecules
Mn-star
Fe3Cr-star
• the top of the valence band is
primarily derived from Fe 3d
and O 2p states
• in the middle part the
structures result from
hybridization of the C 2p, N 2p,
C 2s and N2s states
• at the bottom of the valence
band we have the O2s states
Colossal Magnetoresistance Materials
Characterized by X-ray Spectroscopic
Methods
M. Neumann, K. Kuepper, H. Hesse,
E. Burzo1, I. Balasz1, V.R. Galakhov2
1
Babes Bolyai University, Cluj-Napoca, Romania
2
Russ. Acad. of Sciences, Yekaterinburg
Outline
• Introduction
• Methods: XPS, XES, XAS, XLD, XMCD, RIXS
• CMR materials: © La1-xAxMn1-yTMyO3
© Sr2FeMoO6
( © spinells ACr2X4 )
• Summary
colossal magneto-resistance (CMR)
• The Magneto Resistance is
defined as the change of the
resistance by applying an
external magnetic field
• changes of 100% to several
1000% have been reported
• different applications
Science 292, 1509 (2001)
CMR materials
Colossal magnetoresistance effect (CMR)
© La1-xAxMnO3 =
Science 264, 413 (1994)
Double exchange model (Mn3+, Mn4+) (Zener, PR 81, 440 (1955))
Electron- phonon interaction (Millis et al., PRL 74,
© Sr2FeMoO6
5144 (1995))
high Tc = 420K
low fields for CMR
© Fe1-xCuxCr2S4 ; (ACr2X4 ) =
(Kobayashi et al., Nature 395, 677 (1998))
Nature 387, 268 (1997)
La2-2x (Sr, Ca, Sn)1+2xMn2O7 ( Nature 380, 141 (1996) ); Sr2-xNd1+xMn2O7 ( JPCM 8, L 427 (1996) );
Tl2Mn2O7 ( Nature 379, 53 (1996), Science 273, 81 (1996)); Eu14MnBi11 ( PRB 57, R 8103 (1998) );
Introduction
¾The 3d transition
metal oxides exhibit a
rich variety of electronic
and magnetic properties
¾This is due to the
intricate interplay
between the charge,
magnetic and orbital
degrees of freedom
Manganese perovskites: La1-xAxMnO3
¾ In perovskites like LaMnO3 a
cooperative Jahn-Teller distortion,
i. e. a collective elongation (compression) of one crystal axis may
lead to a preferential occupation of
a certain type of 3d orbital ->
orbital ordering
Methods
• X-ray Photoelectron Spectroscopy (XPS) ⇒ Osnabrück
• X-ray Emission Spectroscopy (XES),
X-ray Absorption Spectroscopy (XAS)
Resonant Inelastic X-ray Scattering (RIXS)
X-ray linear dichroism (XLD)
X-ray magnetic circular dichroism (XMCD)
⇒ ALS, Beamline 8.0.1, SXF and 4.0.2 (XMCD)
⇒ ELETTRA , Beamline BACH, COMIXS (CCD detector)
⇒ BESSY II, Beamline U-41 PGM, ROSA
Mn 3s XPS spectra of Mn oxides
Mn 3s splitting
La1-xBaxMnO3 : XPS VB & XES
d
c
XPS
La0.65Ba0.35MnO 3
LaMnO3
b
XPS
a
Mn Lα XES
Mn Lα XES
O Kα XES
tDOS
pDOS Mn
pDOS O
La0.80Ba0.20MnO3
XPS
Mn Lα XES
Intensity (arb. units)
Intensity (arb. units)
O Kα XES
La0.55Ba0.45MnO3
XPS
Mn Lα XES
O Kα XES
tDOS
La0.45Ba0.55MnO 3
XPS
O Kα XES
Mn Lα XES
tDOS
O Kα XES
11 10 9
8
7
6
5
4
3
2
1
Binding Energy (eV)
0 -1
11 10 9
8
7
6
5
4
3
2
Binding Energy (eV)
1
0 -1
• Strong hybridization of the Mn 3d and O 2p states
La1-xAxMnO3 (A=Ba,Ca):
metal to insulator transition: XPS and RIXS
Ca doped
Ba doped
Ba doped
Ca doped
La1-xAxMnO3: XPS
La1-xAxMnO3: RIXS
x=0.80
x=0.80
x=0.60
Intenisty (arb. units)
x=0.60
Counts
x=0.55
x=0.55
x=0.45
x=0.45
x=0.35
x=0.30
x=0.30
x=0.20
x=0.20
x=0.0
x=0.0
10
9
8
7
6
5
4
3
2
Binding Energy (eV)
1
0
-1
620
630
640
650
Det. Photon Energy (eV)
660
(La,Ba)Mn1-xCoxO3
•
LaCoO3 : Co3+ (3d6) LS state
(no magnetic moment)
La 5p
La0.75Ba0.25MnO3
•
LaMn1-zCozO3: (RPES, XAS)
Intensity (arb. units)
La0.78Ba0.22Mn0.84Co0.16O3
Co2+
O 2s
La 5s
Ba 5p
Ba 5s
40
35
30
VB
25
20
15
10
5
0
Binding energy (eV)
JMMM 210 (2000) 63
• increase of the intensity of the VB
spectrum of the Co-doped (La,Ba)MnO3
at ~2.5÷ 4 eV
• slight changes in the small peak below
EF (eg states) suggest Co bivalent
character, as for La(Mn:Co)O3
La1-xBaxMn1-yCoyO3
3+
LiCo O2
Co 2p3/2
2+
Co O
Intensity (arb. units)
Co 2p1/2
(IML/Isat)LiCoO2 > (IML/Isat)CoO
3+
Co
d (ML-sat)LiCoO2 > d (ML-sat) CoO
La0.74Ba0.26Mn0.88Co0.12O3
La0.75Ba0.25MnO3
Co 2p & Ba 3d
Co 2p spectra analysis:
Co2+
2+
diff (Co )
770
780
790
800
Binding energy (eV)
810
La7/8Sr1/8MnO3: X-ray Linear Dichroism and
Orbital Ordering
Layered manganite LaSrMnO4:
(3z2-r2) - orbital ordering
(PRL 92, 087202)
La7/8Sr1/8MnO3: X-ray Linear Dichroism and
Orbital Ordering
K. Kuepper et al. J. Phys. Chem. B109, 15667 (2005)
La7/8Sr1/8MnO3 : XMCD
Applying the sum rules reveals
a spin moment of +3.8 µB and an orbital moment of approx. -0.3 µΒ
→ total moment 3.5 µΒ.
Sr2FeMoO6
! ordered double perovskite
! poly crystal
! Fe3+ and Mo5+ build up
antiferromagnetic coupling
! shows colossal magneto-resistance
(CMR) at room temperature
! Tc: 410-450 K
! halfmetallic: Up-Spin band shows
band gap, Down-Spin band is metallic
(Nature 395, p. 677, 1998)
! possible application as magnetic
storage
! different theoretical approaches
lead to different interpretation about
the correlation / hybridization
mechanism (Phys. Rev. B 66, 035112
(2002), Phys. Rev. B 67, 085109
(2003))
Y. Tomioka et. al. Phys. Rev. B 61, 422 (2000)
Sr2FeMoO6: magnetic measurements
Intensity (arb. units)
XPS survey spectrum of Sr2FeMoO6
1400
Intensity (arb. units)
Intensity (arb. units)
Sr2FeMoO6: XPS Survey spectrum
Mo 3d
VB
12 10
8
6
4
2
0
Binding Energy (eV)
245
240
235
230
225
220
Binding Energy (eV)
1200
1000
800
600
Binding Energy (eV)
400
200
0
Sr2FeMoO6: XPS core levels
XPS: Mo 3d
XPS: Fe 3s
Intensity (arb. units)
Intensity (arb. units)
Sr2FeMoO6
MoO3
Sr2FeMoO6
FeO
Fe2O3
MoO2
240
235
230
Binding Energy (eV)
225
110
105
100
95
90
Binding Energy (eV)
85
Sr2FeMoO6: XPS, influence of sputtering
Sr2FeMoO6: Mo 3d, Eion=0.5 kV
60 min
30 min
15 min
10 min
60 min
Intensity (arb. units)
Intensity (arb. units)
SFMO: Fe 2p, Eion=0.5 kV
30 min
15 min
10 min
5 min
5 min
scraped
scraped
245
240
235
230
225
Binding Energy (eV)
220
735
730
725
720
715
710
705
Binding Energy (eV)
700
695
Sr2FeMoO6: Mößbauer data
• Mößbauer data fitted with
two sextets and two singlets
•εSM1: 73.6 % bulk
Bhf=47.1T Æ close to Fe 2+
•εSM2: 19.5 % grain boundaries
Bhf=50.3T Æ close to Fe 3+
•εL1 and εL2: antisite defects
•Electron hopping Fe - Mo
valence fluctuations Fe2+/Fe3+
ME gives averaged Bhf
XPS gives a snap shot:
70 % Fe 2+ and 30 % Fe 3+
Sr2FeMoO6: XPS valence band and calculations
Sr2FeMoO6: Valence Band
E
Fe up Saitoh
D
XPS
Intensity (arb. units)
B
A
TDOS Saitoh
Intensity (arb. units)
C
O down
Saitoh
Fe up
Saha-Dasgupta
TDOS Ray
O down
Saha-Dasgupta
9
8
7
6
5
4
3
2
1
0
Binding Energy (eV)
Saitoh et al. (Phys. Rev. B 66, 035112 (2002)),
→ strong hybridization
10
9
8
7
6
5
4
3
2
Binding Energy (eV)
1
0
Saha-Dasgupta et al. (Phys. Rev. B 64, 064408 (2001)) ,
→ strong correlation
Sr2FeMoO6: XPS, XES, band structure
• comparison of the XPS and XES
spectra with new band structure
calculations, use of the lattice
parameters of the best sample as
input parameter!
• Perdew Wang GGA approximation
(calculations performed by
M. Kadiroglu and A. V. Postnikov)
• good agreement between the experimental and the calculated partial
densities of states
• the total density of states have been
derived by weighting the partial
densities of states with help of the
cross sections, good agreement
with the experiment is achieved
Sr2FeMoO6: XPS, XES, band structure
• comparison of the XPS and XES
spectra with new band structure
calculations,
Perdew Wang GGA approximation
• good agreement between the experimental and the calculated partial
densities of states
• the total density of states have been
derived by weighting the partial
densities of states with help of the
cross sections, good agreement
with the experiment is achieved
K. Kuepper et al. J. Phys.: Condens.
Matter 17, 4309 -4317 (2005)
CMR compounds Summary
La1-xSrxMnO3 : x < 0.3, the doping holes have mainly O 2p character
- high value of the Mn 3s splitting (5.3 eV) : the HS state
La1-x (Sr,Ba)x MnO3 : strong hybridization of the TM 3d and O 2p states
La7/8Sr1/8MnO3: strong indications for a cross type (x2-z2)/ (y2-z2) orbital ordering
in the cooperative Jahn Teller distorted phase
XMCD reveals a total magnetic moment of 3.5 µB
Sr2FeMoO6, around 65% Fe2+ and Mo6+, 35% Fe3+, Mo5+ contributions
Sr2FeMoO6, evidence for moderate correlation
Mößbauer reveals about 20% grain boundaries, 4% anti-sites from XRD
Acknowledgements
• G. Borstel, A.V. Postnikov, Univ. Osnabrück
• K.C. Prince, M. Matteucci ELETTRA, Italy
• the group of Prof. F. Parmigiani, Trieste
• Ya.M. Mukovskii, Moscow, Russia
• A. Winiarski, Univ. Katowice, Poland
•helpful assistance at ALS, BESSY and ELETTRA
photo electron emission process (I)
photo electron emission process (II)
Discussions
Magnetic interactions
J’ direct metal to metal exchange
d(M-M) = 5.9-6.3 Å ¨ J’ utterly negligible
J’’ superexchange path M-N-C-N-M
J’’’ superexchange path M-N-C-N-C-N-M
about 0.3-0.4 cm-1
A. Escuer el al., Inorganic Chemistry 39 1668-1673 (2002)
J’’ dominant
semi-Heusler NiMnSb
core level studies
FeStar
first excitation energy
second
third
fifth
forth
1,0
Counts
Fe L3,2 edge
FeStar
0,8
690
695
700
705
710
715
720
725
730
XPS Fe3s
Ferric Star
Intensity (arb. units)
Fe L edge
FeO
115
110
105
100
95
90
85
80
Binding Energy (eV)
735
Fe2O3
Counts
Counts
0,6
∆FeO= ∆FeStar
5
4
3
0,4
2
Counts
Photon Energy (eV)
6
5
1
690
700
710
720
4
3
2
1
730
Photon Energy (eV)
0,2
0,0
700
710
720
Photon Energy (eV)
730
645
660
675
690
705
Emission Energy (eV)
The absoprtion measurements on the FeStar molecule gives us
also Fe2+ which is in a good agreement with the XPS data.
720
core level studies
CrStar
Intensity (arb. units)
Fe 3s
CrStar
110
105
100
95
90
85
Binding Energy (eV)
first excitation energy
second excitation energy
third excitation energy
forth excitation energy
4,0
Fe L2 edge
1,0
3,5
FeL3,2 edge CrStar
CrStar
Counts
Counts
3,0
2,5
2,0
0,5
1,5
2
1
0,0
695
700
705
710
715
3
4
1,0
0,5
720
Photon Energy (eV)
725
730
0,0
640
660
680
700
720
Emission Energy (eV)
740
760
80

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