Ferromagnetism and Persistent Currents in Finely Dispersed Highly Oriented Pyrolytic Graphite Samples

Resumo

Synthesis of finely dispersed graphite powders is described and results of their investigations by the methods of electron microscopy and magnetometry are presented. The samples have been prepared from crystal highly oriented pyrolytic graphite by grinding in an inert atmosphere for a long time with subsequent annealing at 400°C for 24 h in air or in vacuum. It is demonstrated that annealing of the powder in vacuum leads to a considerable increase in the ferromagnetic component associated with the formation of edge defects of zigzag type. The phenomenon of magnetic flux trapping is manifested in the samples annealed both in air and in vacuum upon cooling down to 10 K in a magnetic field that is indicative of the formation of superconducting regions in the samples.