Irreversible magnetic properties of carbon nanoparticles

摘要

Magnetic properties of powder and glassy samples with carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co, are investigated at temperatures T ~ 3 - 300 K in magnetic fields B up to 5 T. Magnetization M (T) exhibits in low fields of B = 1 - 50 mT a strong irreversibility, which is suppressed above B ~ 1 T. The high-temperature (T ~ 200 - 300 K) dependence of Mon B -demonstrates a saturation above B ~ 2 T. Magnetic hysteresis is observed already at 300 K, exhibiting a power-law temperature decay of the coercive field. Analysis of the experimental data suggests a concentration of the magnetization close to the surface of the carbon nanoparticles. This is consistent with the origin of magnetism in nanocarbon due to intrinsic surface defects. Deviations of macroscopic and microscopic parameters in the Co-doped sample from those in the other samples imply an influence of the Co ions and/or clusters.