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H. P. Gunnlaugsson /R. Sielemann, 57 Mn Mössbauer collaboration at ISOLDE/CERN

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

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H. P. Gunnlaugsson /R. Sielemann, 57 Mn Mössbauer collaboration at ISOLDE/CERN

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  1. Magnetism in Iron Implanted Oxides: A Status Report H. P. Gunnlaugsson/R. Sielemann,57Mn Mössbauer collaboration at ISOLDE/CERN

  2. 57Mn Mössbauer collaboration at ISOLDE/CERN Århus: H. P. Gunnlaugsson, G. Weyer CERN: K. Johnston Milan: R. Mantovan, M. Fanciulli Reykjavík: T. E. Mølholt, S. Ólafsson, H. P. Gíslason South Africa: D. Naidoo, K. Baruth-Ram, H. Masenda, W. Dlamini, W. N. Sibanda Leuven: G. Langouche Berlin: R. Sielemann Japan: Y. Yutaka, Y. Kobahashi

  3. 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

  4. Magnetic inventory TM vacancy Transition metal probe Metals alloys componds Dilute magnets Defect magnetism

  5. Minimum needed Diluted magnetic semiconductors Room temperature Ferromagnetism

  6. 57Co (T½ = 271 d) 57Mn (T½ = 1.5 min) 57**Fe (T½ = 8 ns) 57Fe emission Mössbauer spectroscopy Coulomb excited b -ER = 40 eV EC 57MFe (T½ = 98 ns) 14.4 keV, I = 3/2 DE ~ 10-9 eV I = 1/2 57Fe

  7. Mössbauer spectroscopy at ISOLDE/CERN • Highlights: • Low concentrations of probe atoms (~10-4 At.%) • Valence state of Fe • Site symmetry • Magnetic interactions

  8. Implantation of 57Mn

  9. III-V semiconductors No 6-line magnetic pattern! See poster presented by Hilary Masenda (PS3-24)

  10. ZnO without external magnetic field H. P. Gunnlaugsson et al., APL, 2010 (accepted)

  11. ZnO temperature series See talk given by T. Mølholt after this talk

  12. Other oxides: See poster presented by H. P. Gunnalugsson (PS3-23)

  13. Other oxides: MgO T = 77 K See talk given by T. Mølholt after this talk and (PS3-22)

  14. Bhf·g3/2·mI g Bhf·g1/2·mI Mössbauer spectroscopy of magnetic materials 57Mn (T½ = 1.5 min) mI 3/2 57*Fe 14.4 keV T½ = 98 nsI = 3/2 1/2 -1/2 -3/2 DmI = 0, ±1 -1/2 57Fe I = 1/2 Single line resonance detector 1/2

  15. DmI = 0 Ferromagnetism (S = 5/2 good quantum number) Bext g Mössbauer Spectrum Sample Individual line ratios depend on the angle between Bext and g Relative line ratios 3 4 1 1 4 3 3 0 1 1 0 3

  16. Temperatue dependent magnetic order Cold Hot Spins Mössbauer spectra Magnetic hyperfine field • T  Bhf  • No line broadening Bhf TC or TN T

  17. Slow paramagnetic relaxations Coupled(tC) to: Lattice · charge, · phonons Spins · nuclear-· electron- • Conditions for static Bhf • tC ≥ tL (Nucl. Larmor time) • tC ≥ tN(lifetime of Mössbauer state) • Bhf not T dependent • Otherwise broadened 3d J electron spin I HHFI Spin lattice relaxations Spin-spin relaxations ml -2 -1 0 1 2 ml -2 -1 0 1 2 Hdd orHex           Sa ~ Sb Fe3+ (3d5) 6S5/2 Fe2+ (3d6) 5D4 Wss Sa ~ Sb Broadening in MS if >~0.1 at.% Lattice vibrations

  18. -5/2 -3/2 -1/2 +1/2 Few K +3/2 Bext +5/2 Mössbauer spectra of paramagnetic Fe3+ Needs electron spin operators! Low B Plays a role. Combined electronic and nuclear states ±1/2 6S5/2 ±3/2 ±5/2

  19. DmI = 0 from SZ = ±3/2 Paramagnetism (slow relaxation) Bext g Sample SZ = ±5/2 Individual line ratios depend on the angle between Bext and g SZ = ±3/2 SZ = ±1/2

  20. 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)

  21. Slow paramagnetic relaxations at RT plausible?

  22. 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?

  23. Defect magnetism exists! • 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

  24. 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.

  25. Thank you IS443 summer 2009 missing K. Johnston, M. Fanciulli, K. Baruth-Ram, Y. Kobahashi

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