Applications of Mössbauer Spectroscopy at WITS and ISOLDE/CERN by Professor Deena Naidoo Wits-NECSA Workshop September 2015

Outline of Presentation Mössbauer Isotopes/Approaches Measurables WITS Mössbauer Facility and applications Mössbauer at ISOLDE and applications Local and International Collaborations WITS-NECSA Workshop, South Africa, September 2015

Mössbauer Isotopes WITS-NECSA Workshop, South Africa, September 2015

57 Fe Mössbauer Spectroscopy 4 WITS-NECSA Workshop, South Africa, September 2015

Comparison of different MS Approaches Stable 57 Fe (transmission) 57* Fe 57 Co 57 Mn* AccessibleDirect implantation behaviour AccessibleAnnealing, recoil High doses -> interacting Fe atoms. Overlapping damage cascades. Needs large facilities. Low intensity. Spectra masked by implantation damage. Long lifetime. Surface diffusion. Needs large facilities. Competitive proposals. Mössbauer Approaches WITS-NECSA Workshop, South Africa, September 2015

Hyperfine Interactions and Measurables Electric Monopole Interaction Valence/spin state => Position of resonance lines. Electric Quadrupole Interaction Site symmetry => Splitting of lines. WITS-NECSA Workshop, South Africa, September 2015

Hyperfine Interactions and Measurables Magnetic interactions Zeeman splitting into 6-line pattern. Other Measurables  Spin relaxation rates (sextet broadening).  Diffusion on a atomic scale (line broadening).  Interaction with defects (implantation damage/lattice sites).  Debye temperature (resonance area/intensity). WITS-NECSA Workshop, South Africa, September 2015

Be Window Mössbauer WITS WITS-NECSA Workshop, South Africa, September 2015 Transmission MS CEMS Some Electronics Some Research Samples Fly-ash Multiferroics Milled carbides with binders Cemented carbides Catalysts Carbon nanomaterials Rock bearing samples

Be Window Apllications: WITS – Fly Ash WITS-NECSA Workshop, South Africa, September 2015

Be Window Applications: WITS – Cemented Carbides WITS-NECSA Workshop, South Africa, September 2015

ISOLDE: Beam Production Proton induced fission in UC 2 target  Neutron rich isotopes Laser  Selective ionisation, Mn Electromagnet  Mass selection ( 57 Mn ) 1.4 Acceleration to keV WITS-NECSA Workshop, South Africa, September 2015

On-line emission Mössbauer spectroscopy 57 Mn decay to the 57 Fe probe: 57 Fe 57* Fe (τ = 140 ns) I = 3/2 I = 1/2 57 Co (T ½ = 271 days) 57 Mn (T ½ = 85.4 sec.) EC -- Off-line γ 14.4 keV Mössbauer transition Ion-implantation of dilute dopants into sample Resonance detector v WITS-NECSA Workshop, South Africa, September 2015

Be Window Beamline ( 57 Mn + ions) Implantation Chamber Mössbauer Drive Resonance Detector To Electronics and data acquisition Counting Gas ISOLDE, CERN WITS-NECSA Workshop, South Africa, September 2015

Why Radioactive Beams (RIB)? ISOLDE On-Line Isotope Mass Separator No problems with beam contamination. Beam intensity (~2× Mn/s).. Total dose of ≤ Mn/cm Mn  57 m Fe ( T ½ = 1.5 min.)  E R  ~ 40 eV. Study impurities <10 -5 at%). Study impurities (~10 16 atoms/cm 3 <10 -5 at%). High statistics spectrum (5 – 10 min). Isothermal annealing studies on a timescale of minutes. Dose dependence. Measurements at different emission angles. External magnetic field ( B ext ≤ 0.6 T). Quenching WITS-NECSA Workshop, South Africa, September 2015 Some Research Samples Diamond, SiC, GaN, AlN, InN, Si, Ge, Al 2 O 3, MgO, ZnO (+ nanowires), TiO 2, SnO 2, GaAs, InP, GaP, FeV multilayers, Heusler Alloys, Topological insulators,

Si Mn Upon annealing of implantation damage (T > 450 K, t = 90 sec) Mn enters predominantly substitutional sites or near- substitutional sites WITS-NECSA Workshop, South Africa, September 2015

Si Mn 57* Fe 57 Mn (T ½ = 1.5 min.) 57* Fe 14.4 keV (  = 140 ns)  - = 40 eV 57 Fe  WITS-NECSA Workshop, South Africa, September 2015

Applications: ISOLDE - Silicon WITS-NECSA Workshop, South Africa, September 2015

Emission Channeling in ISOLDE Four fractions: Random fraction (R) => disordered environment. Ideal substitutional site (S) Near substitutional site (near-S) Near interstitial site (near-T) WITS-NECSA Workshop, South Africa, September 2015

Applications: ISOLDE - ZnO B ext = 0 T: Complex magnetic sextet structure. Magnetic structure originate from Kramers doublets. NO ordered magnetism. Slow Relaxing Paramagnetism. WITS-NECSA Workshop, South Africa, September 2015

Some Collaborators at CERN South Africa: D. Naidoo, K. Bharuth-Ram, H. Masenda and M. Ncube acknowledges support from South African National Research Foundation and the Department of Science and Technology. Denmark: H.P. Gunnlaugsson, G. Weyer and M.B. Madsen. acknowledges support from MIUR through the FIRB Project RBAP115AYN “Oxides at the nanoscale: multifunctionality Italy: R. Mantovan and M. Fanciulli acknowledges support from MIUR through the FIRB Project RBAP115AYN “Oxides at the nanoscale: multifunctionality and applications”. Iceland: T.E. Mølholt, S. Ólafsson and acknowledges support H. P. Gíslason acknowledges support from the Icelandic Research Fund. CERN-ISOLDE: K. Johnston Belgium: G. Langouche Germany: R. Sielemann WITS-NECSA Workshop, South Africa, September 2015

Local Collaboration  Professor D. Naidoo (Group Leader)  Dr H. Masenda  Undergraduate Students (Physics Majors III and Materials Science III)  Postgraduate Students (Honours, MSc and PhD)  School of Physics: MPRI Members  Modelling Group DST/NRF CoE in Strong Materials  School of Chemistry  School of Geosciences  University of Johannesburg  Durban University of Technology (DUT)  MINTEK/ANGLO/CSIR/SASOL/ELEMENT 6  NECSA – future? WITS-NECSA Workshop, South Africa, September 2015