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“Magnetic” Impurities in Ammonia Treated Fullerenes

CNISM. “Magnetic” Impurities in Ammonia Treated Fullerenes. Daniele Pontiroli. CNISM. Outline. Fullerenes treated with NH 3 The Mössbauer effect Experimental results Chemical analysis techniques Conclusions. NH 3. C 60 H x N y. CNISM. C 60 Treated with NH 3.

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“Magnetic” Impurities in Ammonia Treated Fullerenes

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  1. CNISM “Magnetic” Impurities in Ammonia Treated Fullerenes Daniele Pontiroli

  2. CNISM Outline • Fullerenes treated with NH3 • The Mössbauer effect • Experimental results • Chemical analysis techniques • Conclusions

  3. NH3 C60HxNy CNISM C60 Treated with NH3 • Reaction in steel autoclave • Pristine C60 (99.8 %) alternately with or without 8% NH4Cl (catalyst) put in a quartz chamber and shaken by a mechanical stirrer • NH3 is introduced at 6-7 atm at room temperature • The system is heated at 200- 500°C (P = 10 - 18 atm) B. P. Fokin, Yu. M. Shulga, E. E. Fokina, I. I. Korobov, A. G. Burlakova, B. P. Tarasov ISJAEE 6 (2004) 20

  4. C60Treated withNH3 • Hysteresis cycle in fresh sample (Ms=2.2 emu/g) at 300 K T. Makarova, F. Palacio, “Carbon Based Magnetism”, ed. Elsevier (2006), chapter 24

  5. 3 2 K 4.5 K 2 25 K 50 K 1 100 K M (emu/g) 200 K 0 300 K -1 -2 -3 -50 0 50 aging effects H (kOe) C60 Treated with NH3 • Hysteresis cycle in fresh sample (Ms=2.2 emu/g) at 300 K • Hysteresis loops in the same sample after 8 months at several T • Reduction of Ms of ~20% after 8 months T. Makarova, F. Palacio, “Carbon Based Magnetism”, ed. Elsevier (2006), chapter 24

  6. C60 Treated with NH3 • Chemical analysis performed on the samples: HR-ICP-MS by HE4 • In FA2 1% -Fe is enough to take into account the whole Ms of the sample! • In FA14 Fe, Co, Ni can explain 80 % of the measured saturation magnetisation (Ms = 0.024 emu/g) The FM behaviour is due to impurities!

  7. The Mössbauer Effect • Local measure of the electronic and magnetic environment of the 57Fe nucleus • Very short process time-scale determined by Heisemberg principle: DEDt ~ h/2p DE  10-9 eV Dt  10-7 s  rays (E = 14.4 KeV) Moving emitter (57Co in Rh) Absorber: sample with Fe Counter

  8. The Mössbauer Effect Is

  9. data fit Mössbauer Results • Presence of a doublet in FA2 at 300 K (B = 0) • Isomeric shift Is compatible with Fe(III) 1 0.99 Fe is NOT in ferromagnetic form! Relative Intensity 0.98 0.97 0.96 -10 -5 0 5 10 Velocity (mm/s)

  10. data data fit fit site a site b Mössbauer Results • A nonmagnetic state was found also at 77 K • No superparamagnetic blocking was found 1 • Asymmetry of the fit compatible with two sites for Fe(III) 0.99 Relative Intensity • No match with Fe3C 0.98 0.97 -5 0 5 Velocity (mm/s)

  11. Mössbauer Results • Comparison with the behaviour of poly-C60 treated with Fe provided by HE3 data 1 fit • Presence of a sextet at 300 K due to Fe3C and traces of -Fe 0.99 Relative Intensity 0.98 0.97 0.96 -5 0 5 Velocity (mm/s) A. Talyzin, A. Dzwilewski, L. Dubrovinsky, A. Setzer, and P. Esquinazi, cond-mat/0602306

  12. X-ray Analysis of FA2 • Laboratory Powder diffraction on FA2(CuK) 7 C60 6 NH4Cl • No evidence of polymeric structures 5 4 Intensity (arb. units) • Two phases: pristine C60 and NH4Cl 3 2 • No evident presence of impurities 1 0 10 20 30 40 50 Angle 2 (degrees)

  13. Considerations • FA2 sample is a very “dirty” sample • The impurities may derive from the interaction of the NH4Cl with the steel of the autoclave* • 57Fe Mössbauer spectroscopy revealed that iron in the sample is not in ferromagnetic state • From HR-ICP-MS (by HE4) results the ferromagnetic behaviour is not completely explained by impurities but… *A. Samide, I. Bibicu, M. S. Rogalski and M. Preda, J. Radioanalytical and Nuclear Chemistry 261- 3 (2004) 593

  14. Optically detected Inductively Coupled Plasma analysis (ICP-AES) by CNISM: ! ! ! New Chemical Analysis • EDAX performed by HE3 indicated the presence of 2 % Ni in FA2 sample

  15. Chemical Analysis Techniques • All the techniques permit to obtain high sensitivity for our purposes WHY WERE DIFFERENT RESULTS OBTAINED?

  16. “Digestion” of the sample by a mixture of nitric and sulphuric acid NO2+ + H3O++ 2H2SO4 HNO3 + 2H2SO4 Work in progress! (Collaboration with Chemistry Department of University of Parma) Chemical Analysis Techniques • The complete mineralisation of the sample is a very important task! • Not complete mineralisation of the sample R. Taylor, “The Chemistry of Fullerenes”, ed. World Scientific (2003)

  17. Conclusions • C60HxNy FA2 compound is a very “dirty” sample, in which ferromagnetic behaviour probably is due to the impurities • No evidence of ferromagnetic Fe came from Mössbauer analysis (down to 77 K) • XRD analysis is not suitable to evidence the presence of impurities • Chemical analyses based on the solution of the sample are strongly affected by the extent of the sample “digestion” Thank you for your attention!

  18. 0.04 0.02 M (emu/g) 0 -0.02 -0.04 -20 -10 0 10 20 H (kOe)

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