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Emission Mössbauer Spectroscopy at ISOLDE/CERN

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Emission Mössbauer Spectroscopy at ISOLDE/CERN 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 in Bext Magnetic order Bext m = 0 I g Sample 57*Fe 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) Relative emission (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.
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