X-ray Photoelectron Spectroscopy (XPS)and Magnetism
• Part I IntroductionExperimentalPrinciples of XPS and SRPESSelected results (intermetallic, organometallic, spinels)
• Part IIInvestigation of oxidic CMR compounds by XPS and complementary techniques
IntroductionAbbreviations:PES Photoelectron SpectroscopyXPS X-ray (excited) PESESCA Electron Spectroscopy for Chemical Analysis SRPES Spin-resolved Photoelectron SpectroscopyUPS Ultraviolet (excited) PESARUPS Angle Resolved UPSXES X-ray (Photon) Emission SpectroscopyXAS X-ray Absorption SpectroscopyXMCD X-ray magnetic circular dichroismXMLD 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 – EbinEvac = 0
one electron type picture
electron mean free path
Experimental
Light sources:
XPS: Al Kα radiation (1486.7 eV), also monochromatisedSynchrotron 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
XES
XPS AESvacuum level
core level
fluorescence
photo electron Auger electron
photon
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
Inte
nsity
(arb
. uni
ts)
240 235 230 225Binding Energy (eV)
MoO3
Sr2FeMoO6
XPS: Mo 3d
MoO2
Mo6+ and Mo5+ ions in Sr2FeMoO6
reference compoundsMo6+ in MoO3Mo4+ in MoO2the Mo 3d states are splitdue to LS-coupling
exchange splitting
1s XPS spectra of paramagnetic moleculesshow a splitting due to the interactionof 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 SXPS probes the final state S ± ½in well screened systems charge istransferred from O2p to 3d statesplus spin-spin interactions
A, B with charge transfer (CT) C, D without CT (less screening)
3s splitting in TM oxides
valence bandtDos and pDos
Co2MnSn (Heusler alloy)
tDos (total densities of states)probed by XPSpDos (partial densities of states)probed by XEScomparison with theoryspin resolvedsmall gap?
Detection of Spin Polarization
SPLEED detector (Omikron)Mini Mottdetector (SPECS)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
Alvarado, Campagna and Hopster
Dietz
Dietz and Kuhlenbeck (1984) Campagna 1985
SRPES from Fe 3s
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)
HS: 2 Sz componentsLS: 1 Sz component
HS
LS
SRPES with cicularly polarized light from nonmagnetic metals
total intensities:
I(f5/2) : I(f7/2) = 3 : 4highly 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 2000G. 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 sitescan close the gap and also reduce the spin polarization.
Heusler-AlloysX2MnZ
• local magnetic moment at the Mn-atom 2,3µB - 4,4 µB
• Mn3d : delocalised band; hybridisation with the X 3d electrons
• Mn3d : localised unoccupied states
• magnetic coupling by the Z element
L21 Heusler-Alloys with Mn or Cr
Fe2MnZ
Co2MnZ
semi-Heusler
A2CrAl
Co2MnZ
660 655 650 645 640 635 630
Fe2MnSi
Mn2p1/2
Mn2p3/2
Fe2MnAl
Co2MnSb
Co2MnSn
Co2MnGa
Co2MnAl
Inte
nsitä
t (be
l.Ein
heite
n)
Bindungsenergie (eV)
Mn2p core levels
Mn2p3/2 splitting vs. µMn
-1,0 -0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 40,00,10,20,30,40,50,60,70,80,91,01,11,21,31,41,51,61,71,8
Ni2MnSn
Co2MnSn
PdRh2Mn
Cu2Mn
Ni2MnSb
NiCo2MnSb
Co2MnSnCo2MnGa
Co2MnAl
Fe2MnSi
Fe2MnAl
2MnSnSn
Al
MnSb
Experiment
Theory
µMn (µB)
∆E
(eV
)
,0 4,5
Mn 2p photoelectron spectra
A comparison with atomic spectrademonstrates the localized nature of the Mn 2p states in MnOmultiplet effects need to be includedin calculations
Local moments also in Heuslers!
Ph. Wernet et. al. Phys. Rev. B (2001)
chalkogenide spinels
Fe1-xCuxCr2S4
Ramirez et al., Nature, 386, 156 (1997)
Chalkogenide spinelsprepared byV. Tsurkan (Kishinau)
Cr
Fe
SFe2+Cr3+
2S2-4
CuCr2S4 : Lotgering : Cu1+ (Cr3+, Cr4+)
Goodenough : Cu2+ (Cr3+)
Fe0.5Cu0.5Cr2S4: Cu1+ Fe3+ / Cr4+ / S-
x= 0 x= 0.5
FeCr2S4 Fe0.5Cu0.5Cr2S4
15 10 5 0
Cr Lα
S L2,3
S Kβ
Fe 3d
Fe Lα
Cr 3d
S 3pS 3s
Inte
nsity
(arb
. uni
ts)
Binding energy (eV)15 10 5 0
S L2,3
S Kβ
S 3p
Cu Lα
Fe Lα
Cr Lα
Cr 3d
Cu 3d
Fe 3dS 3s
Inte
nsity
(arb
. uni
ts)
Binding energy (eV)
- 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 .
• contribution from the Cu3d states just below Cr 3d.
J. Phys.: Condens. Matter 12, 5411 – 5421 (2000)
Cu 2p & 3s XPS spectra
• no satellite in the Cu 2p spectra of Fe0.5Cu0.5Cr2S4
• no exchange splitting for the Cu 3s state
⇒ 3d10 configuration of the Cu+ ion
970 960 950 940 930
*
Cu 2p1/2
Cu 2p3/2
Cu(1+)FeO2
Cu(2+)O
Cu2O
Fe0.5Cu0.5Cr2S4
Binding energy (eV)
Inte
nsity
(arb
. uni
ts)
110 115 120 125 130 135
Cu 3s
Binding energy (eV)
Inte
nsity
(arb
. uni
ts)
Fe 2p & S 2p XPS spectra
738 732 726 720 714 708
*
Fe2+Cr2S4
Fe3+2O3
Fe 2p1/2
Fe 2p3/2
Inte
nsity
(arb
. uni
ts)
Binding energy (eV)
168 164 160 Binding energy (eV)
S 2p1/2
S 2p3/2
Fe0.5Cu0.5Cr2S4 polycrystal Fe0.5Cu0.5Cr2S4 * FeCr2S4
Additional features in thepolycrystal‘ spectrumØ wrong interpretation of the experimental data !
The importance of usingsingle crystals !!!
charge transfer from S2- to Fe3+ : Fe2+
CuCr2Se4
126 124 122 120 118
CuCr2Se4
Fe0.5Cu0.5Cr2S 4
Cu 3s
B inding energy (eV)
Inte
nsity
(arb
. uni
ts)
No exchange splitting of Cu 3s ⇒ Cu+ character of the Cu ions
PRB 59 (1999) 14552
10 8 6 4 2 0 -2
Se 4p
Cr 3d
Cu 3d
Inte
nsity
(arb
. uni
ts)
Binding energy (eV)
970 960 950 940 930
Cr LMM
Cu 2p3/2
CuCr2Se4
Cu 2p1/2
Binding energy (eV)
Inte
nsity
(arb
.uni
ts)
FeCr2S4
Fe 3s
Cr 3s
Inte
nsity
(arb
. uni
ts)
70 80 90 100 110
MnCr2S4
Mn 3s
Cr 3s
Binding energy (eV)
• the same Cr 3s exchange splitting ∆Eex (~ 4 eV) for all compounds
similar values for the local magnetic moments of Cr Cr 3+ ions
∆Eex(Fe) = 5.4 eV
Fe2+
Mn2+
TM 3s splittingSol. St. Comm. 114 (2000) 149
∆Eex(Mn) = 5.7 eV
Cr 2p XPS spectra
570 575 580 585 590
(e)
(d)
(c)
(b)
(a)
Cr 2p1/2
Cr 2p3/2In
tens
ity (a
rb.u
nits
)
Binding energy (eV)
ACr2S4 (A= Zn, Mn, Cd, Fe, Fe :Cu)
570 575 580 585 590
(d)
(c)
(b)
(a)
Cr 2p1/2
Cr 2p3/2
Inte
nsity
(arb
.uni
ts)
Binding energy (eV)
BCr2Se4 (B = Cd, Hg, Hg: Cu, Cu)
Eur. J. B 15 (2000) 401
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 structurecalculations
organometallic materials
XPS on organometallic materials
ferric wheel
ferric star
Magnetic moleculesSynthesized by R.Saalfrank et al.Erlangen
di-cyanamidesmolecule based solids
Dicyanamide materials M[N(CN)2]2M = Mn, Fe, Ni, Cu
• each metal ion is surrounded bysix nitrogen atoms in a distorted(axially elongated) octahedralgeometry
• the rutile-like structure consists of rhombus-shaped units whichadopt a chain alignment parallelto the c axis
• tilting of the elongated octahedrain the crystallographic ab plane
M
N(2)
N(1)C
M
M = Mn, Fe, Co, Ni, Cu
change over
Dicyanamide materials M[N(CN)2]2M = Mn, Fe, Ni, Cu
Crystallographic data - isostructural series
M
M
N(2)
N(1)C
unit cell
C.R. Kmety et al.Physical Review B, 62 5576-5588 (2000)
change over
Magnetic moments on Mn:4.65 µB/atom Mn[N(CN)2]24.45-4.79 µB/atom MnO
• the magnetic moment per Mn atom is slightly reduced as expected from a Mn2+ (3d5) ion due to a reductionin spin polarization driven by Mn(3d) N(2sp) interaction.
Dicyanamide Mn[N(CN)2]2 3s splitting
J‘‘ dominant super exchange path
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 DOSN 2p DOSC DOSC 2p DOS
Mn DOSMn 3d DOS
Phys. Rev. B66, 014446(8) (2002)
filling of eg and t2g levels is important for the super exchange interaction, and responsible for the change over AFM - FMHOMO: Mn : majority spin
LUMO : minority spinD.O.Demchenko et al. Phys. Rev. B 69, 205105(9) (2004)
[Li⊂Fe6L6]Cl*6CHCl3, L=N(CH2CH2O)3
prepared by Saalfrank et al. Erlangen
ferric wheel
Fe 3d +O 2p
N, C2p
C2sN2s
O2s
[Li⊂Fe6L6]Cl*6CHCl3, L=N(CH2CH2O)3
Valence bands ferric wheel
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)
Fe-star
Fe3Cr-star
Mn-star
ferric starmolecules
• 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 isdefined as the change of theresistance by applying an external magnetic field
• changes of 100% to several1000% 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, 5144 (1995))
© Sr2FeMoO6 high Tc = 420K
low fields for CMR (Kobayashi et al., Nature 395, 677 (1998))
© Fe1-xCuxCr2S4 ; (ACr2X4 ) 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
The 3d transition metal oxides exhibit a rich variety of electronic and magnetic properties
This is due to the intricate interplay between the charge, magnetic and orbitaldegrees of freedom
Manganese perovskites: La1-xAxMnO3
In perovskites like LaMnO3 a cooperative Jahn-Teller distortion, i. e. a collective elongation (com-pression) 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 splitting
Mn 3s XPS spectra of Mn oxides
La1-xBaxMnO3 : XPS VB & XES
• Strong hybridization of the Mn 3d and O 2p states
11 10 9 8 7 6 5 4 3 2 1 0 -1
pDOS O
pDOS Mn
d c ba
tDOS
XPS
O Kα XES
Mn Lα XES
LaMnO3
Inte
nsity
(arb
. uni
ts)
tDOS
O Kα XES
Mn Lα XES
XPS
Binding Energy (eV)
La0.80Ba0.20MnO3
11 10 9 8 7 6 5 4 3 2 1 0 -1
O Kα XES
Mn Lα XESXPS
La0.65Ba0.35MnO3
Inte
nsity
(arb
. uni
ts)
tDOS
O Kα XES
XPS
Mn Lα XES
La0.55Ba0.45MnO3
La0.45Ba0.55MnO3
Binding Energy (eV)
XPS
O Kα XES
Mn Lα XES
La1-xAxMnO3 (A=Ba,Ca): metal to insulator transition: XPS and RIXS
Inte
nist
y (a
rb. u
nits
)
10 9 8 7 6 5 4 3 2 1 0 -1
Binding Energy (eV)
x=0.20
x=0.0
x=0.30
x=0.45
x=0.55
x=0.60
x=0.80
Ba doped Ca doped
La1-xAxMnO3: XPS
Cou
nts
660650640630620Det. Photon Energy (eV)
Ca doped Ba doped
La1-xAxMnO3: RIXS
x=0.0
x=0.30
x=0.20
x=0.35
x=0.55
x=0.45
x=0.60
x=0.80
40 35 30 25 20 15 10 5 0
La0.75Ba0.25MnO3
VB
O 2sLa 5s
Ba 5s
La 5p
Ba 5p
La0.78Ba0.22Mn0.84Co0.16O3
Inte
nsity
(arb
. uni
ts)
Binding energy (eV)
(La,Ba)Mn1-xCoxO3
JMMM 210 (2000) 63
• increase of the intensity of the VB spectrum of the Co-doped (La,Ba)MnO3at ~2.5÷ 4 eV• slight changes in the small peak belowEF (eg states) suggest Co bivalent character, as for La(Mn:Co)O3
• LaCoO3 : Co3+ (3d6) LS state(no magnetic moment)
• LaMn1-zCozO3: (RPES, XAS) Co2+
La1-xBaxMn1-yCoyO3
770 780 790 800 810
Co 2p1/2
La0.74Ba0.26Mn0.88Co0.12O3
La0.75Ba0.25MnO3
diff (Co2+)
LiCo3+O2
Co2+O
Co 2p3/2
Co3+
In
tens
ity (a
rb. u
nits
)
Binding energy (eV)
Co 2p & Ba 3d Co 2p spectra analysis:
Co2+
(IML/Isat)LiCoO2 > (IML/Isat)CoO
d (ML-sat)LiCoO2 > d (ML-sat) CoO
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
Y. Tomioka et. al. Phys. Rev. B 61, 422 (2000)
ordered double perovskitepoly crystal Fe3+ and Mo5+ build up
antiferromagnetic couplingshows colossal magneto-resistance
(CMR) at room temperatureTc: 410-450 Khalfmetallic: Up-Spin band shows
band gap, Down-Spin band is metallic (Nature 395, p. 677, 1998)
possible application as magnetic storage
different theoretical approacheslead to different interpretation aboutthe correlation / hybridizationmechanism (Phys. Rev. B 66, 035112 (2002), Phys. Rev. B 67, 085109 (2003))
Sr2FeMoO6: magnetic measurements
XPS survey spectrum of Sr2FeMoO6
Inte
nsity
(arb
. uni
ts)
1400 1200 1000 800 600 400 200 0Binding Energy (eV)
Sr2FeMoO6: XPS Survey spectrum
Inte
nsity
(arb
. uni
ts)
245 240 235 230 225 220Binding Energy (eV)
Mo 3d
Inte
nsity
(arb
. uni
ts)
12 10 8 6 4 2 0Binding Energy (eV)
VB
Sr2FeMoO6: XPS core levelsIn
tens
ity (a
rb. u
nits
)
240 235 230 225Binding Energy (eV)
MoO3
Sr2FeMoO6
XPS: Mo 3d
MoO2 In
tens
ity (a
rb. u
nits
)
110 105 100 95 90 85
Binding Energy (eV)
XPS: Fe 3s
Fe2O3
FeO
Sr2FeMoO6
Sr2FeMoO6: XPS, influence of sputtering
735 730 725 720 715 710 705 700 695
60 min
30 min
15 min
10 min
5 min
scraped
SFMO: Fe 2p, Eion=0.5 kV
Inte
nsity
(arb
. uni
ts)
Binding Energy (eV)245 240 235 230 225 220
60 min
30 min
Sr2FeMoO6: Mo 3d, Eion=0.5 kV
15 min
10 min
5 min
scraped
Inte
nsity
(arb
. uni
ts)
Binding Energy (eV)
Sr2FeMoO6: Mößbauer data
• Mößbauer data fitted withtwo sextets and two singlets
•εSM1: 73.6 % bulkBhf=47.1T close to Fe 2+
•εSM2: 19.5 % grain boundariesBhf=50.3T close to Fe 3+
•εL1 and εL2: antisite defects
•Electron hopping Fe - Mo valence fluctuations Fe2+/Fe3+
ME gives averaged BhfXPS gives a snap shot:
70 % Fe 2+ and 30 % Fe 3+
Sr2FeMoO6: XPS valence band and calculationsIn
tens
ity (a
rb. u
nits
)
10 9 8 7 6 5 4 3 2 1 0Binding Energy (eV)
Sr2FeMoO6: Valence Band
XPS
TDOS Saitoh
TDOS Ray
AB
C
D
E
Inte
nsity
(arb
. uni
ts)
9 8 7 6 5 4 3 2 1 0Binding Energy (eV)
Fe upSaha-Dasgupta
O down Saha-Dasgupta
O down Saitoh
Fe up Saitoh
Saitoh et al. (Phys. Rev. B 66, 035112 (2002)), → strong hybridization
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 byM. Kadiroglu and A. V. Postnikov)
• good agreement between the experi-mental 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 experi-mental 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 orderingin 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)
Magnetic interactionsDiscussions
J’ direct metal to metal exchanged(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-Mabout 0.3-0.4 cm-1
A. Escuer el al., Inorganic Chemistry 39 1668-1673 (2002)
J’’ dominant
semi-Heusler NiMnSb
corecore levellevel studiesstudiesFeStar
645 660 675 690 705 720
first excitation energy second third fifth forth
Cou
nts
Emission Energy (eV)
700 710 720 730
0,0
0,2
0,4
0,6
0,8
1,0
Cou
nts
Photon Energy (eV)
Fe L3,2 edge FeStar
1234
5
690 695 700 705 710 715 720 725 730 735
Cou
nts
Photon Energy (eV)
Fe L edge FeO
115 110 105 100 95 90 85 80
XPS Fe3sFerric Star
Inte
nsity
(arb
. uni
ts)
Binding Energy (eV)
∆FeO= ∆FeStar
690 700 710 720 730
1
2
3
4
5
6
Cou
nts
Photon Energy (eV)
Fe2O
3
The absoprtion measurements on the FeStar molecule gives usalso Fe2+ which is in a good agreement with the XPS data.
corecore levellevel studiesstudiesCrStar
640 660 680 700 720 740 7600,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
Cou
nts
Emission Energy (eV)
first excitation energy second excitation energy third excitation energy forth excitation energy
Fe L2 edge CrStar
695 700 705 710 715 720 725 7300,0
0,5
1,0
Cou
nts
Photon Energy (eV)
FeL3,2 edge CrStar
23 4
1
110 105 100 95 90 85 80
Inte
nsity
(arb
. uni
ts)
Binding Energy (eV)
Fe 3sCrStar
