Emission Mössbauer Spectroscopy at ISOLDE/CERN
Torben Esmann Mølholt
ISOLDE Seminar, 25. Nov. 2015 Outline
Experimental setup at ISOLDE
Brief on the Mössbauer spectroscopy technique
Examples and Results
Future/ongoing measurements
2 Acknowledgements
The Mössbauer collaboration at ISOLDE/CERN, >30 active members with new members (2014) from China, Russia, Bulgaria, Austria, Spain: Four experiments Existing members New members 2014 (IS-501, IS-576, IS-578, I-161)
3 Emission Mössbauer Spectroscopy at ISOLDE/CERN http://e-ms.web.cern.ch/
GLM (GPS)
LA1-2 (HRS)
4 119In RILIS 2014 2015 57Mn 119 RILIS In
15 μSi/h - 57Mn 10 μSi/h - RILIS
5 μSi/h -
0 μSi/h -
5 Mössbauer Experimental setup
Implantation chamber Incoming 60 keV beam
Sample
Faraday cup Be window Mössbauer drive with resonance detector Container: 25 mbar acetone
• Intensity (~1×108 atoms/s) • High statistics spectrum (5 – 10 min.) •On-line (short lived)
•Collections for Off-line (long lived) 6 •Hours - days Mössbauer Experimental setup Sample holder
•Temperature range 90 – 700 K • Measurements at different emission angles
• Applied magnetic field
(Bext ≤ 0.6 T)
7 Mössbauer Experimental setup Sample holder
• Quenching:
Implant at high temperature
Measure at low temperature (off-line)
8 Mössbauer Experimental setup Resonance detector - G. Weyer, Mössbauer Eff. Meth., 10 (1976) 301 PPAD: Parallel Plate Avalanche Detector - Single line resonance detector. 0.1 cps (~0.1 µCi) – 50k cps (~500 mCi)
9 Mössbauer spectroscopy technique
10 40-60 keV Ion-implantation of Mössbauer Probe Emission Mössbauer spectroscopy
Measurement of spectrum
v E(v) Eγ 1 γ c
Source/sample: – v + v ion-implanted crystal Absorber/detector: Single line resonance detector
Mössbauer spectroscopy: Counts High spectral resolution v = ±10 mm/s (Doppler) E = ±4.8×10-7 eV –10 0 +10 Velocity (mm/s) Emission11 Mössbauer spectrum Emission Mössbauer spectroscopy
Measure hyperfine interactions
Important info on an atomic scale:
• Valence/Spin state (line position, d) Hyperfine interactions • Site symmetry Mössbauer transition E = 10-8 eV (doublet?) • Magnetic interactions (Sextet) • Binding properties Dilute Probe: Below 10-3 at.% • Relaxation effects 1×1018 atoms/cm3 • Diffusion ….. 12 The resolution of Mössbauer spectroscopy can measure hyperfine interactions Cubic: Single line
• Position of spectral line
Valence state emission Relative
Velocity [mm/s]
Non-cubic: Split line
• Quadropol splitting
Cubic?
emission Relative
Velocity [mm/s]
13 Valence/Spin state 57Fe emission Mössbauer spectroscopy Spectral line position, Isomer shift, d
Shielding ↑ r(0) ↓, d ↑
1 mm/s = 48 neV 14 57Fe emission Mössbauer spectroscopy Magnetic hf. splitting of 57Fe Sextet m 1 2 3 4 5 6 I If the spin is stable for longer +3/2 than 140 ns – Sextet is observed 57* Fe 14.4 keV +1/2 I = 3/2 -1/2 Ferromagnetic material -3/2
57Fe -1/2 I = 1/2 57*Fe +1/2
Bhf 0, Vzz 0 1 2 3 4 5 6
Slow relaxing paramagnetism
(not only one sextet) Relative emission Relative
- v 0 + v 57*Fe Relative velocity
15 Angular dependence 57*Fe in Bext Magnetic order
Bext m = 0 I g Sample
Individual line ratios depend on the angle
between Bext and the γ direction
Relative line ratios: 3 40 1 1 40 3 3:4:1 (90º) 3:0:1 (0º)
16 Angular dependence in Bext 57*Fe (same as ordered, but Kramer doublets) Paramagnetism (slow relaxation)
mI = 0 from SZ = ±3/2 Bext g Sample
SZ = ±5/2 Individual line ratios depend on the angle SZ = ±3/2 between Bext and the γ direction SZ = ±1/2
Relative line ratios: 3:4:1 (90º) 3:0:1 (0º) 17 Sample of interest (Crystal, solid)
- Implant Radioactive probes / impurities
- Decay Probe the crystal
- The radioactive decay gives information about the probe sites SPECTRUM (data)
- Analysis of Spectra (data) Crystal properties Ion-implantation
Beam
19 Examples and results
20 Interstitial in MgO 77 K Quenched from ca. 650 K
-6 -4 -2 0 2 4 6 Velocity (mm/s)
Quenching setup: ca. 650 K
Reduction of FeD (damage) - “More clear” FeI line
- Low statistics spectrum (no FeMag)
-6 -4 -2 0 2 4 6 Velocity (mm/s)
21 T. E. Mølholt et al. J. Appl. Phys. 115, 023508 (2014) Magnetic identification
ZnO at 300 K D2 D3 B = 0.6 T║c g Magnetic structure originate ext Bext θ ~ 60° from Kramers doublets is
mI = 0 from SZ = ±3/2 clearly observed.
±1/2 ±3/2 ± 5/2
B ext= 0.6 T║c • NO ordered magnetism Bext θ ~ 0° g
Relative emission (arb. units) Relative emission (arb. • Slow relaxing Paramagnetism
±1/2 ±3/2 ± 5/2
-12 -9 -6 -3 0 3 6 9 12 Velocity (mm/s) - T. E Mølholt, Paramagnetism in ion-implanted oxides (2012) ISBN: 978-9935-9069-5-3 - H. P. Gunnlaugsson et al. , Appl. Phys. Lett. 97 (2010) 142501 22 Paramagnetic relaxation of dilute 57Fe? ZnO at 300 K D2 Ion-implanted D3 57Mn+ , c ~ 30° g Know it is of paramagnetic origin: B = 0 ext (a) Examine temperature dependence of the c ~ 60° g paramagnetic structure
g B = 0 T: B = 0.6 T║c Bext ext ext (b) More complex magnetic sextet structure θ ~ 60°
±1/2 ±3/2 ± 5/2
Bext B ext= 0.6 T║c g Relative emission (arb. units) emission Relative (arb. θ ~ 0° (c)
±1/2 ±3/2 ± 5/2
-12 -9 -6 -3 0 3 6 9 12 Velocity (mm/s) 23 Temperature ↑ : Broadening ↑
ZnO: B = 0 T Blume M. and Tjon J.A.: ext simulation Phys. Rev. 165, 446 (1968) B = ±50 T ~ 2 ns 445 K 664 K hf
~ 4 ns 411 K 644 K ~ 13 ns
~ 50 ns
mission 373 K 607 K
e e ~ 140 ns
Relative emission Relative tiv
a 338 K 552 K
l
e R >> 140 ns 300 K 515 K
-12 -8 -4 0 4 8 12 -10 -5 0 5 10 -10 -5 0 5 10 Velocity (mm/s) 2c Velocity (mm/s) 1 E0 - T. E Mølholt et al. Physica Scripta, T148 (2012) 014006 - T. E Mølholt et al. Hyp. Int. 197(2010)24 89-94 Spin-lattice relaxation rates in studied oxides - T. E Mølholt et al. Physica Scripta, T148 (2012) 014006 - T. E Mølholt et al. Hyp. Int. 197 (2010) 89-94 - H.P. Gunnlaugsson et al. Hyp. Int. 198 (2010) 5-14 1×109- R. Mantovan et. al. Advan. Elec. Mat. 1 (2015) 1400039
) ZnO
1 Theory -
s a-Al2O3 ( 8
1×10 MgO Direct 2 phonon /
1 process T 2 process , 2
e T t 7
a 1×10 r
T 5-9
on
i t
a 9 6 T
x 1×10 Log(rate) a 1
l T e R θ /3 1×105 D ~20 K ~qD/3 70 100 300 1000 Log(T) Temperature (K) MgO: ~ 730 K
qD α-Al2O3: ~ 1050 K ZnO: ~ 300 – 700 K 25 On-going and future Mössbauer studies at ISOLDE
Make use of more ISOLDE beams - On-line - Off-line (longer lived Mossbauer isotopes), b508
Please see Talk at the ISOLDE Workshop by Haraldur Páll Gunnlaugsson: - Friday 4th Dec. 09:30
26 151Eu Mössbauer
151 151 June/July 2015: Dy-beam, T½~124d ( Gd) RE doping: manipulate optical properties in semiconductors Samples made in minutes Measurements of ~20 samples ongoing
3 Period 2 4 Au Cu 5 1 6 Ni 0 2 4 6 8 10 Ag 12 14 16 -1
-2
-3
Isomer shift(mm/s) -4 Pd Nb Pt Ta W Ir -5 Mo -6 Group
F.E. Wagner27 et. al., Physics Letters A 42, 7, (1973) 483 151 1.02 Cu sample. Eu
1.01 Measured at RT
1 As implanted
0.99
0.98
Exprerimental 0.97 Simulation
Relative Transmission Relative Eu3+
0.96 Eu2+ Eu3+
0.95 Implantation related sites -20 -15 -10 -5 0 5 10 15 20 - Damage (not perfect lattice) - Vacancies 1.04 Velocity (mm/s) - Interstitial
1.02
1 After annealing: 0.98 350°C for 30 min.
0.96
0.94
Exprerimental Relative Transmission Relative Simulation 0.92 Eu3+ Substitutional site Eu2+ 0.9 -20 -15 -10 -5 0 5 10 15 20
Velocity (mm/s) 28 197Au Mössbauer
197 November 2015: Hg beam, T½~64h Test for Bio-physics (INTC-2015-008, I-161). Low Hg-yields to LA2 (sample made in several hours): → No bio-physics. But proof of feasibility/calibration. 1.020
1.015
1.010
1.005
1.000
Relative Transmission Relative 197 197 0.995 Hg → Au Au foil at 77 K (LN2) Measured for 3 days. On-going measurement. as implanted. 0.990 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 Velocity (mm/s)
29 Emission Mössbauer at ISOLDE
! The ISOLDE isotope beams are our tools for Mössbauer studies !
Usage of additional isotopes for extended studies and possibilities
30 Conclusions
Mössbauer is a unique atomic-scale measurements of electronic, magnetic, and structural properties within materials. ISOLDE is the perfect tool to create and study doping and defects in materials.
Showed some specific results. Interstitial Fe in MgO. Paramagnetism is oxides.
Expanding the isotopes used for eMS at ISOLDE. Further doping possibilities. Bio-physics. Thanks for your attention
31