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Recent Magnetic Results on Rhombohedral C 60

Recent Magnetic Results on Rhombohedral C 60. S.Buga, M. Belli, M.Mazzani, D.Pontiroli, A.Goffredi, M.Riccò. FerroCarbon Final Meeting Crete, September 2008. Outline. Introduction Magnetic Measurements Room Temperature Ferromagnetism Polymer Sructure and Ferromagnetism

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Recent Magnetic Results on Rhombohedral C 60

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  1. Recent Magnetic Resultson Rhombohedral C60 S.Buga, M. Belli, M.Mazzani,D.Pontiroli, A.Goffredi, M.Riccò FerroCarbon Final Meeting Crete, September 2008

  2. Outline • Introduction • Magnetic Measurements • Room Temperature Ferromagnetism • Polymer Sructure and Ferromagnetism • Discussion and conclusions

  3. Depolymerizes at 430 – 450 K Rhombohedral C60

  4. Synthesis Parameters • Samples of Pressure-induced Rh C60 polymer were obtained by high-pressure high-temperature treatment of pristine C60 : • Duration 30’ • Pressure 5.5 GPa • Temperature different for each samplerange from 775° to 900°C

  5. Magnetic Measurements • The samples were handled in air • The pellets were broken in an agate mortar to obtain small fragments • Magnetic Characterization included • A magnetization curve M(H) at 300 K, recorded varying the field from +5 T to -5 T • Magnetization as a function of temperature(Field Cooling and Zero Field Cooling)and Low temperature M(H) (for some samples only) • All the measurements were performed with automatic background subtraction.

  6. Untreated sample

  7. Diamagnetic &Ferromagnetic Contributions • In each sample there’s a weak Ferromagnetic contribution(few hundreds µemu/g)

  8. Diamagnetic &Ferromagnetic Contributions • Samples synthesized at 800°C reproducibly show a much stronger Ferromagnetic contribution(few memu/g)

  9. Room-Temper. Ferromagnetism Significantly strong ferromagnetic contribution is observed only in samples synthesized at 800°C 800° C 825° C 850 °C 900° C

  10. Room-Temperature Ferromagnetism Ferromagnetism is obtained only in case of very SPECIFIC CONDITIONS OF SYNTHESIS

  11. Ball-Milled Sample One of the magnetic samples (synthesized at 800°C) underwent ball-milling in condition similar to ball-milling of graphite and… …the polymer lattice was completely destroyed

  12. …the ferromagnetic contribution increased or, considering inhomogenities of these samples,did not change Conclusion:Ferromagnetism does not dependon polymer structure

  13. Conclusions • Relatively strong room-temperature ferromagnetism was confirmed in Rh-C60 synthesized in very specific conditions • We can exclude it come from impurities as other sample does not show such an high magnetic signal • Ferromagnetism seems not to depend on rhombohedral polymer structure

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