h. p. gunnlaugsson /r. sielemann, 57 mn mössbauer collaboration at isolde/cern
DESCRIPTION
Magnetism in Iron Implanted Oxides: A Status Report. H. P. Gunnlaugsson /R. Sielemann, 57 Mn Mössbauer collaboration at ISOLDE/CERN. 57 Mn Mössbauer collaboration at ISOLDE/CERN. Århus : H. P. Gunnlaugsson, G. Weyer CERN : K. Johnston Milan : R. Mantovan, M. Fanciulli - PowerPoint PPT PresentationTRANSCRIPT
H. P. Gunnlaugsson/R. Sielemann,
57Mn Mössbauer collaboration at ISOLDE/CERN
Magnetism in Iron Implanted Oxides: A Status Report
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
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
Magnetic inventory
vacancy
TM
Transition metal probe
Metals alloys
componds
Dilute magnets
Defect magnetis
m
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
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
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
Implantation of 57Mn
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!
-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)
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
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)
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
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
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
Temperatue dependent magnetic order
Bhf
Spins
Mössbauerspectra
Magnetic hyperfine field
TC or TN
T
-T Bhf
- No line broadening
Cold Hot
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.%
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
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
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)
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
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?
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
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.
Thank you
IS443 summer 2009 missing K. Johnston, M. Fanciulli,
K. Baruth-Ram, Y. Kobahashi