Giant Paramagnetism and Ferromagnetism of Copper Nanoparticles in a Carbon Matrix

Solid-phase pyrolysis of polycrystalline copper phthalocyanine (CuPc, Pc=C₃₂N₈H₁₆) yielded Cu nanoparticles encapsulated in a graphite-like carbon shell - Cu@C nanocomposites. Magnetic measurements in series of average sizes of copper nanoparticles in the range of 5-40 nm were conducted by a vibrational magnetometer in the temperature range 10-300 K and magnetic field up to the 60 kOe. Giant paramagnetism, apparently due to conduction electrons with ballistic mean free path (large orbital magnetism) was detected for nanoparticles with small average size of Cu nanoparticles, 5-7 nm. At temperature T= 10K the value of the specific susceptibility is of order 1.5×10^-4 emu/gOe. Ferromagnetism (Ms ≈ 0.5 emu/gCu) was also detected in Cu@C nanocomposites from helium up to room temperature.