Magnetometry on treated ball-milled graphite

1. Magnetometry on treated ball-milled graphite M.Mazzani, D.Pontiroli, M.Belli, A.Goffredi, M.Riccò FerroCarbon Final Meeting Crete, September 2008

2. Interests inBall-Milling of Graphite • Defects • Role of hydrogen • Production of graphene-likestructure and edges Results No reproducible room-temperature ferromagnetism

3. 20 Starting Ball-Milled Graphite H2 @ 100°C 10 0 M-Mdia (10-3 emu/g) -10 Measurement at 30°C -20 -10 -5 0 5 10 Applied Field (Oe) Preliminary Studies • September 2007first samples of H2 treated ball-milled graphite • Relatively strong ferromagnetism:Saturation Magnetization up to 37 memu/g

4. Summary • Optimization of ball-milling procedure • Characterization of ball-milled graphite • Hydrogen treatments from H2 generatorand production of FerroMagnetic samples • Hydrogen treatments from H2 tanksand recent magnetic results • Discussion and conclusions

5. Ball-Milling Procedure • Use of powder graphite RW-A (SGL Carbon):mesh 240, content of Fe <0.2 ppm, previously treatedin vacuum 1 night at 800°C • Optimization of the ball-milling parameters(time, frequency, mass amount of the sample) in order to introduce a large quantity of defectswithout producing amorphous carbon • Final configuration300 mg of graphite in an agate grinding bowl with 3 balls. Milling at 50 Hz for 1 hour (intervals of 10’ milling + 5’ pause)

6. in-plane vacancies edges ball milling Turbostratic disorder Characterization of Ball Milled GraphiteMorphology

7. Crystallite size along the stacking c-axis Characterization of Ball Milled GraphiteMorphology 10 nm • Production of 6 nm – tick crystalliteas confirmed by TEM and Raman • Production of graphene layers

8. Characterization of Ball Milled GraphiteParamagnetism (Tc = -17 ± 0.2 K) C = 4.5 10-5 emu K / g Oe One of the main effects of ball-milling is the production of Paramagnetic centers

9. Characterization of Ball Milled GraphiteM(H) at 300K : Diamagnetism

10. Characterization of Ball Milled GraphiteAgeing (I) Ageing effects are evidenced by • uSR (missing fraction) • Raman • Reactivity to hydrogen as seen by SQUID

11. Characterization of Ball Milled GraphiteAgeing (II) Ageing does not affect paramagnetic signal, i.e. ageing process does not involve paramagnetic centers

12. First set of samples – Winter 2007/08Hydrogenation ofball-milled graphite

13. First set of samples – Winter 2007/08Treatment Conditions • Ball-milling always performed in theoptimal conditions • Samples always handled in controlled atmosphere • Hydrogenation performed at high temperatures in our CVD apparatus • H2 from a hydrogen generator • Flux of hydrogen (80 ml/min) • Each treatment lasted for 2 hours

14. First set of samples – Winter 2007/08Treatment Conditions Quartz vessel and sample

15. First set of samples – Winter 2007/08Magnetic Results SQUID magnetometry evidenced a relatively strong ferromagnetic contribution at 300K in some of the samples

16. First set of samples – Winter 2007/08Magnetic Results Inhomogeinity of the magnetic contributions among these samples led to discover that ball-milled graphite is affected by AGEING

17. Guidelines for a newset of samples • Any treatment of ball–milled graphite must be done immediately after milling • We should exclude impurities coming from the experimental apparatus • Some tests revealed H2 from the generator has water impurities(a few drops could be condensed from over 70l of H2 .We could estimate 100-300 ppm of water) • Separate effects of water and hydrogen

18. Second set of samples – Summer 2008Treatment conditions • Ball-milling always performed in theoptimal conditions • Samples always handled in controlled atmosphere • Any treatment done on freshly milled graphite • For treatments we used a completely different experimental environment(different pipes, vacuum fittings and valves) to check for impurities

19. Second set of samples – Summer 2008Samples exposed to… • Hydrogen • pure anhydrous hydrogen from H2 tanks • “static” exposure • Temperature range-200 to + 200°C • Water • Air

20. Second set of samples – Summer 2008Magnetic Results Just to refresh magnetic properties of BMG…

21. Second set of samples – Summer 2008Magnetic Results Exposure to hydrogen at low temperatures (liquid nitrogen) and at 25°, 100°, 200°C No or very weak increase in ferromagnetism

22. Exposure to water At 25°C and at high temperatures (400°C) to reproduce previous treatments conditions One sample exposed to water at 25°C and treated in vacuum at high temperatures (400°C) to remove intercalated water No or very weak increase in ferromagnetism Second set of samples – Summer 2008Magnetic Results

23. Second set of samples – Summer 2008Magnetic Results Temperature dependence of magnetization exhibit Curie behaviour. For example…

24. Second set of samples – Summer 2008Magnetic Results Comparing Temperature dependence of magnetization among the different samples and starting BMG

25. Second set of samples – Summer 2008Data for Ferromagnetic contributions

26. Sample of freshly BMG exposed to air:Diamagnetism and Ferromagnetism

27. Sample of freshly BMG exposed to air:Paramagnetism

28. Sample of freshly BMG exposed to air:Discussion • From Impurities?(reproducibility tests needed) • We have excluded ferromagnetism derives from pure hydrogen or distilled “degased” water. From the presence of both in air as in the CVD apparatus…? • From oxygen? • From other air components?

29. Conclusions • No sistematically ferromagnetic samples were produced from BMG • Some strongly FM samples arose some interest and would require further studies • Ball-milling produces multi-graphene and graphene-like structures, with a relatively high density of edges.Investigations on them continues…

31. Ageing by Raman

32. EPR hydrogen Intensity (arb.units) Magnetic Field (Oe)

33. EPR on air exposed BMG

34. Low temperature FM in BMG

35. Raman Grafite Macinata

36. Ruolo dei Difetti

37. Le forme del Carbonio 2DIM Grafene