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Magnetic order in Kapton ? J. Barzola, D. Spemann, A. Setzer, P.E.

Magnetic order in Kapton ? J. Barzola, D. Spemann, A. Setzer, P.E. C. N. O. A „simple“, quasi two-dimensional polyimide structure C 22 H 10 N 2 O 5. Magnetic order in a Polyimide (C-H-O-N) ????. Kaburagi and Hishiyama, J. Mater. Res. 17 , 2000 (2002).

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Magnetic order in Kapton ? J. Barzola, D. Spemann, A. Setzer, P.E.

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  1. Magnetic order in Kapton ? • J. Barzola, D. Spemann, A. Setzer, P.E.

  2. C N O A „simple“, quasi two-dimensional polyimide structureC22H10N2O5

  3. Magnetic order in a Polyimide (C-H-O-N) ???? Kaburagi and Hishiyama, J. Mater. Res. 17, 2000 (2002)

  4. Results for virgin Kapton samples of different thickness Virgin Polyimide Sample Magnetic impurities < 1 ppm Ferromagnetic background with Tc > 300 K

  5. Sample 1-50 Negligible FM Paramagnetic contribution due to 2 multiplets separated by D ~ 650K

  6. Sample 4-50 Clear FM contribution Multiplet contribution with D ~ 250 K

  7. Changes in the T-dependence after low temperature annealing (370K) in SQUID Maximum in m(T) appears after annealing  Changes in the Paramagnetic contribution. Three samples show the same behavior after heating them to 370K.

  8. Annealing at high T in external oven (25 µm thick samples) 600°C 1000 °C

  9. Annealing at high T in external oven (50 µm thick samples) Behavior reproduced in 6 samples No increase in FM saturation, only remanent moment. Increase of Paramagnetism Virgin Annealed at 853 K for 1h.

  10. After annealing 1h at 750K in SQUID oven

  11. Annealed Polyimide several hours at 750K in SQUID oven Remanence m(H=0) Two FM transitions: Tc ~ 4 K Tc ~ 800 K Intrinsic or Impurities ? 10 kOe Brillouin Fct. with „Tc“ = 780K

  12. PIXE Measurements What is that ? Average concentration Fe ~ 3 ppm, i.e. factor ~10 larger than in virgin samples ! 800 µm

  13. PIXE measurements with the proton µ-beam All Fe-grains are at the surface • Concentration results indicate the existence of grains of • Magnetite Fe3O4 (Tc = 858 K), or • Ni Ferrite NiFe2O4 (Tc = 858 K) 50 µm

  14. Conclusions • Weak FM signals (~ 10-4 emu/g) in some virgin samples with Tc > 400 K. Fe-impurity concentration below 0.3 ppm and not at the surface. • Temperature dependence indicates: Non simple Curie-like Paramagnetism with a sample dependent multiplet contribution. Sensitive to low-T annealing. • Weak increase in FM remanence at low T after high T annealing (T > 750K). • Introduction of impurities through the SQUID oven (~10 µm Fe-based grains) ! • PIXE measurements are unavoidable for this kind of studies

  15. Brillouin Fct. Tc=380K Curie law Irradiated HOPG: low current, 110K

  16. New Trends in Solid State PhysicsTwo dimensional electron properties of graphite graphene

  17. Quantum Hall Effect in Bulk Graphite (2003) PRL 90, 156402 (2003)

  18. Quantum Hall Plateaus in a Corbino Disk geometry of oriented graphite (2006)

  19. Nature 2005 „graphene“

  20. GraphiteA laboratory to test relativistic electrons ? Nature 2005

  21. Both, Dirac and „normal“ fermions contribute in bulk graphite (with disorder) • Zhou et al., Nature Physics (2006) Annals of Physics (2006) • Luk‘yanchuk and Kopelevich, PRL (2006) • Lu et al., PRL (2006)

  22. Number of Publications in Physical Review Letters and PRB (only) on graphene

  23. Future Aims Relativistic quasiparticles in a solid Preparation and transport characterization of (ideal) multigraphene- Influence of the QHE on disorder- Spin-orbit coupling in graphite- Quantum Interference effects of Dirac Fermions- Trigger large Magnetoresistance at Room Temperature in Multigraphene- Magnetic order via irradiation and/or disorder

  24. Ferromagnetic Critical Temperature

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