Features of magnetic resonance in nanoporous carbon with pores filled with transition-metal atoms

Properties of nanoporous carbon (NPC) free of metal atoms and NPC containing atoms of Ni, Co and Pd in their pores are studied by electron spin resonance (ESR). The asymmetrical ESR line with the so-called Dyson line shape points out that charge carriers are responsible for the resonance spectrum in metal-free NPC. Although the amount of Ni, Co, and Pd introduced into nanopores is small, the NPC properties change significantly. A bulk ferromagnetism is observed in the case of NPC with Co and Pd, but not in NPC:Ni. Co atoms in pores of NPC cause the formation of a new material, namely, a disordered ferromagnetic medium with some features in the Co atom distribution. Magnetic properties are strongly temperature-dependent. The temperature dependences of the conductivity and ESR integral intensity in NPC:Ni reveal an exponential growth with the same activation energy. The magnetic resonance spectrum of NPC:Pd consists of four signals for NPC which is produced from SiC. There are one ferromagnetic and three paramagnetic signals belonging to the carbon dangle sp³- and sp²-bonds kind and to the paramagnetic clusters of Pd atoms.