Magnetic Properties of Fullerene–Thermally Exfoliated Graphite Composites Doped with Sodium

The magnetic properties (field range H = 0–50 kOe, temperature range T = 3–300 K), and structural features of a sodium-doped carbon composite material based on fullerene C 60 and thermally exfoliated graphite (TEG) are studied. The material is obtained with different ratios of the components by sintering at a pressure of 7 GPa and T = 600°C, at which it is found that significant amorphization of the crystal lattice of the initial C 60 occurs. The dia-, para-, and ferromagnetic components ( M D , M PM , and M FM ) were separated from the total magnetic moment of the samples under study. It is found that a sodium dopant has no effect on the magnetic properties of the composite. Analysis of the M PM ( H ) field dependences by using the Brillouin function for the fullerene-containing sample (i.e., without TEG) makes it possible to determine the quantum number of the total angular momentum of paramagnetic (PM) centers. Its value is found to be J = 1, which corresponds to elementary magnetic moment μ PM = 2μ B of a PM center. The concentration of PM centers is estimated at the level of N PM ≈ (2–5) × 10 18 g –1 for most samples, including the material without TEG. The introduction of TEG into the initial composition and an increase in its proportion in the composite leads to a strong increase in the magnetic moment, which is explained by an increase in both the J value and the concentration of PM centers.