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Investigating Room Temperature Ferromagnetism in Rhombohedral C60: Synthesis and Magnetic Properties

This study presents the synthesis and magnetic characterization of pressure-induced rhombohedral C60 samples. Conducted at temperatures between 775°C and 900°C, ferromagnetic behavior was observed primarily in samples synthesized at 800°C and higher, indicating strong room-temperature ferromagnetism under specific synthesis conditions. Magnetic measurements, including M(H) curves, revealed weak ferromagnetic contributions in all samples, but significant improvements were noted at higher synthesis temperatures. The results suggest that ferromagnetism in Rh-C60 is independent of polymer structure and not due to impurities.

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Investigating Room Temperature Ferromagnetism in Rhombohedral C60: Synthesis and Magnetic Properties

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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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