Multilevel ferromagnetic behavior of room-temperature bulk magnetic graphite

Abstract

In this paper we report on the magnetic properties of pure bulk ferromagnetic graphite, obtained by a chemical route previously described. This magnetic graphite has been obtained by a vapor reaction consisting of a controlled etching on the graphite structure. By magnetic force microscopy we have verified that its magnetic properties are related to the topographic defects introduced in the pristine material. Also, the magnetic properties have been verified through magnetization measurements as a function of temperature and applied magnetic field. At low temperatures $(2\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ the saturation magnetization reaches a value of $0.58\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕\mathrm{g}$, leading to a defect concentration of $1250\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$. The system is highly irreversible due to the inhomogeneity of the distribution of defects in the material. Two transition temperatures are detected, ${T}_{\mathrm{c}1}=115(5)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{c}2}=315(5)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These transitions could be associated to the weak coupling between ferromagnetic regions related to defects and to the ferromagnetism inside the defect regions.