H. P. Gunnlaugsson /R. Sielemann, 57 Mn Mössbauer collaboration at ISOLDE/CERN
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Transcript of H. P. Gunnlaugsson /R. Sielemann, 57 Mn Mössbauer collaboration at ISOLDE/CERN
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H. P. Gunnlaugsson/R. Sielemann,
57Mn Mössbauer collaboration at ISOLDE/CERN
Magnetism in Iron Implanted Oxides: A Status Report
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Århus: H. P. Gunnlaugsson, G. Weyer CERN: K. JohnstonMilan: R. Mantovan, M. FanciulliReykjavík: T. E. Mølholt, S. Ólafsson, H. P. GíslasonSouth Africa: D. Naidoo, K. Baruth-Ram, H. Masenda, W. Dlamini, W. N. SibandaLeuven: G. LangoucheBerlin: R. SielemannJapan: Y. Yutaka, Y. Kobahashi
57Mn Mössbauer collaboration at ISOLDE/CERN
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Magnetism in Iron Implanted Oxides: A Status Report
Motivation (Magnetism in TM doped oxides)
Physical/technical introduction (CERN Mössbauer)
Experimental spectra Mn/Fe in ZnO and others
Ordered Magnetism versus Paramagnetism
Conclusion
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Magnetic inventory
vacancy
TM
Transition metal probe
Metals alloys
componds
Dilute magnets
Defect magnetis
m
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0
200
400
600
800
1000
1200
1400
1600
0 0.5 1 1.5 2
Spins/atoms
TC o
r T
N (
K)
Ferromagnetism
Minimum needed
Room temperature
Diluted magneticsemiconductors
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57Fe emission Mössbauer spectroscopy
57Fe
57MFe (T½ = 98 ns)14.4 keV, I = 3/2
I = 1/2
57Co (T½ = 271 d)57**Fe (T½ = 8 ns)57Mn (T½ = 1.5 min)
EC
Coulombexcited-
ER = 40 eV
~ 10-9 eV
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Mössbauer spectroscopy at ISOLDE/CERNProton Booster
Synchrotron
1.4 GeV p+
UC2 target
LaserSelective ionization of Mn and Sn
Accelerationto 60 keVImplantation
chamber
Mass separation
Mössbauer drive system and detector
~6108 At. s-1
Highlights:-Low concentrations of probe atoms (~10-4 At.%)
-Valence state of Fe
-Site symmetry
-Magnetic interactions
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Implantation of 57Mn
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III-V semiconductors
See poster presented by Hilary Masenda (PS3-24)
-5 -4 -3 -2 -1 0 1 2 3 4 5
Velocity (mm/s)
Rel
ativ
e em
issi
on (
arb.
uni
ts) GaAs
426 K
300 K
-Damage site-Substitutional Fe-Fe-V complexes
No 6-line magnetic pattern!
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-12 -9 -6 -3 0 3 6 9 12
Velocity (mm/s)
Em
issi
on (
arb.
uni
t)
B ext = 0 Tq = 60o
ZnO without external magnetic field
H. P. Gunnlaugsson et al., APL, 2010 (accepted)
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ZnO temperature series
-10 -7.5 -5 -2.5 0 2.5 5 7.5 10-10 -7.5 -5 -2.5 0 2.5 5 7.5 10
Rel
ativ
e em
issi
on (
arb.
uni
ts)
Velocity (mm/s)
450 K
433 K
370 K
366 K
339 K
300 K
837 K
795 K
664 K
579 K
522 K
494 K
See talk given by T. Mølholt after this talk
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1.0
1.5
2.0
2.5
3.0
-12 -8 -4 0 4 8 12
Velocity (mm/s)
Rel
ativ
e em
issi
on Al2O3
T = 300 K
Other oxides:
See poster presented by H. P. Gunnalugsson (PS3-23)
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See talk given by T. Mølholt after this talk and (PS3-22)
-12 -8 -4 0 4 8 12
Velocity (mm/s)
Rel
ativ
e em
issi
on
77 KFeS FeIFeD
Other oxides:
MgOT = 77 K
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Mössbauer spectroscopy of magnetic materials
Single line resonance detector
57Mn (T½ = 1.5 min)
57*Fe 14.4 keVT½ = 98 nsI = 3/2
57Fe I = 1/2
mI
3/2
1/2-1/2-3/2
1/2
-1/2
Bhf·g3/2·mI
Bhf·g1/2·mI
mI = 0, ±1
BµB IgH NNˆˆ
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Ferromagnetism (S = 5/2 good quantum number)
Bext
SampleMössbauer
Spectrum
Relative lineratios
Individual line ratios depend on the angle between Bext and
3 4 1 1 4 33 0 1 1 0 3
mI = 0
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Temperatue dependent magnetic order
Bhf
Spins
Mössbauerspectra
Magnetic hyperfine field
TC or TN
T
-T Bhf
- No line broadening
Cold Hot
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Slow paramagnetic relaxations
IJ
HHFI
3dLattice · charge, · phonons
Spins · nuclear- · electron-
Coupled(C) to:
electron spin
Lattice vibrations
Fe2+ (3d6)5D4
Fe3+ (3d5)6S5/2
ml
-2-1012
ml
-2-1012
Spin lattice relaxations
Sa ~ Sb
S ~ S
ss
Hdd orHex
)exp(
12
12 EE
HH exddss
Spin-spin relaxations
Conditions for static Bhf
C ≥ L (Nucl. Larmor time)C ≥ N (lifetime of Mössbauer state) Bhf not T dependent Otherwise broadened
Broadening in MS if >~0.1 at.%
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Mössbauer spectra of paramagnetic Fe3+
Needs electron spin operators!
...ˆˆˆˆˆ NQIHFIEZICF HHHHH
±1/2±3/2
±5/2
6S5/2
+5/2
+3/2
+1/2
-1/2
-3/2
-5/2
Bext
Few K
SSHCFˆˆˆ D SµH BEZI
ˆˆ gB
Low B
SIH HFIˆˆˆ A
Plays a role. Combined electronic and nuclear states
High B (> 0.3 T)
Kramer doublets give sextets with
Bhf |SZ|
-12 -8 -4 0 4 8 12
Velocity (mm/s)
±5/2
±3/2
±1/2
Sum
High B (> 0.3 T)
Kramer doublets give sextets with
Bhf |SZ|
-12 -8 -4 0 4 8 12
Velocity (mm/s)
±5/2
±3/2
±1/2
Sum
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Paramagnetism (slow relaxation)
Bext
Sample
Individual line ratios depend on the angle between Bext and
SZ = ±5/2
SZ = ±3/2
SZ = ±1/2
mI = 0 from SZ = ±3/2
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ZnO at RT in Bext = 0.6 T
Sextet originating from Kramer doublets clearly observed
No relaxation at RT?
H. P. Gunnlaugsson et al., APL, 2010 (accepted)
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Slow paramagnetic relaxations at RT plausible?
Temperature (K)
109
108
107
106
105
104
103
102
101100 102 103
Spi
n re
laxa
tion
rat
e (s
-1)
T1 data from
Tribollet et al.,(2008)
Broadening in MS
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Does defect magnetism exist?
In ZnO, implanted Mn/Fe Fe3+ shows slow paramagnetic relaxations
-> No spin-spin relaxations with defects
<- Theory overestimates range of magnetism from isolated defects (Zunger et al., 2010), data misinterpretated and precipitation not documented (Potzger et al., 2008+)
Is defect or dilute magnetism myth?
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Defect magnetism exists!
-10 -5 0 5 10-10 -5 0 5 10
Velocity (mm/s)
Rel
ativ
e em
issi
on (
arb.
uni
ts)
10 -10
Poly-crystalline
(iii)
HOPG (ii)
HOPG (i)14 K
40 K
100 K
200 K
25 K
295 K
Sext D2D1
S1
D2D1
S1
-Implantation of 57**Fe into Graphite
-Sextet (Fe2+) observed at 14 K
-Reduced Bhf at 40 K (not a static Bhf)
Sieleman et al., PRL, 2007
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Conclusions/summary-Implanted Mn/Fe ions in oxides lead to TM in various charge states and lattice sites
-Fe as 3+ state has extremely long relaxation time and displays static (para)-magnetic spectra. Most extreme case Fe in ZnO.
-Application of external magnetic field decouples perturbing fields and yields spectrum looking like an effective magnetic field.
-Identification of defect related magnetism by Mössbauer spectroscopy has been observed at very low temperatures in graphite.
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Thank you
IS443 summer 2009 missing K. Johnston, M. Fanciulli,
K. Baruth-Ram, Y. Kobahashi