Defect annealing in Mn /Fe implanted TiO 2 (rutile)
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Defect annealing in Mn/Fe implanted TiO2 (rutile)H. P. Gunnlaugsson on behalf of the Mössbauer collaboration at
ISOLDE/CERN (IS501)
• Motivations• Experimental• Results• Discussion/conclusion
2
TiO2 (rutile) motivations
Very radiation hard: Can only be made amorphous by implantation at T < 77 K or extreme fluences (>>1 dpa)Possible host for upconversionReports on dilute magnetism
O2-
Ti4+
Er3+: ZnO, TiO2, …
3
Experimental57Mn for 57Fe Mössbauer spectroscopy
General principle:
Implantation of short lived parent isotopes
57Mn (1.5 min.)
57Fe
Resonancedetection
g
Major benefits- Fe charge state (Fe3+/Fe2+)- Fe site symmetry- Fe3+ spin relaxation
- High dilution ~10-4 at.%- Creation of defects
ER ~ 40 eVER,max = 93 eV
Mössbauer spectroscopy/Hyperfine interactions: Sensitive only to nn – nnn effects
4
Results: Temperature series
-12 -8 -4 0 4 8 12
329 K
357 K
477 K
541 K
603 K
662 K
-12 -8 -4 0 4 8 12
143 K
182 K
220 K
262 K
305 K
315 K
Fe2+
SL
-12 -8 -4 0 4 8 12
329 K
357 K
477 K
541 K
603 K
662 K
Velocity (mm/s)
Rel
ativ
e em
issi
on (a
rb. u
nits
)
-12 -8 -4 0 4 8 12
143 K
182 K
220 K
262 K
305 K
Dominated by Fe2+ speciesSingle line (SL) component at highest T’sSomething on the wings… consistent with slow relaxing paramagnetic Fe3+
SL due to Fe3+
5
Results: Angular dependence
-12 -8 -4 0 4 8 12
Rel
ativ
e em
issi
on (a
rb. u
nits
)
Velocity (mm/s)
q = 80 �
q = 60 �
q = 0 �
T = 143 K
-12 -8 -4 0 4 8 12
Rel
ativ
e em
issi
on (a
rb. u
nits
)
Velocity (mm/s)
q = 80 �
q = 60 �
q = 0 �
T = 220 K
Clear angular dependenceFe2+ can probe the lattice structure through the quadrupole interaction
6
Results: Spectral area
Pure TiO2: Fe as Fe3+
+ Oxygen vacancies (VO)
Fe2+
+ Titanium vacancies (VTi)
Fe3+(/4+)
0102030405060708090
100
100 200 300 400 500 600 700
Are
a fr
actio
n (%
)
Temperature (K)
Fe(II)
Fe(III) + SL
Fe2+/3+
VO
VTi
Fe2+/3+
VO
VTi
Fe2+
VO
Fe2+ Fe3+
7
Pair disociation
Probability of dissociation:
)ln(½)(1
)(
0AA
0
0
kTETpe
eTpkT
E
kTE
Complex: Diss. Energy Binding energy [Navarro et al., 2011] (theory)
Mn – VO: 1.60(15) eV ~1.6 eV:
Mn V
0
8
Fe3+ relaxation rates- We find -1 T4(1)
- Theory suggests T2
- Similar inconsistency in ZnO [Mølholt et al., Phys. Scripta, 2011]
- Reason for this is unknown
1.E+00
1.E+08
2.E+08
3.E+08
4.E+08
5.E+08
6.E+08
100 200 300 400 500 600 700
τ-1(H
z)
Temperature (K)
cE2
01
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
100 1000
τ-1(H
z)
Temperature (K)
MgO, Al2O3: T2
ZnO: T9
9
Discussion/summary57Mn implantations into TiO2 single crystals and Mössbauer measurements on the daughter 57Fe A model of the annealing: VO stabilize Fe2+ state at T < 550 K VTi promote Fe3+ state at T < 330 K
VO-Mn(/Fe) dissociation energy Experimental (here) 1.60(15) eV Theory [Navarro11] ~1.6 eV
No defect related magnetism is found, but paramagnetism with “abnormal” temperature dependenceNo interstitial Fe displacement energy > 93 eV, consistent with theory (~130 eV [Thomas et al., 2005])
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