Room-temperature ferromagnetism in hydrothermally treated glassy carbon

• Room-temperature ferromagnetism in hydrothermally treated glassy carbon systems.
• Strong correlation between ferromagnetic response and diamagnetic susceptibility.
• Systematic correlation between graphitization process and graphitic cluster size.

Extraordinary room-temperature ferromagnetism was observed in our hydrothermally treated glassy carbon systems, taken to comprise nearly graphitized regions. Strong correlation between the ferromagnetic response and the diamagnetic susceptibility, superposed together, suggests the ferromagnetic long-range order in the graphitic phase to be of itinerant nature. Besides, the graphitization process associated with the itinerant spins and the ferromagnetic order revealed a systematic correlation with the average graphitic cluster size.