Coexistence of Ferromagnetism and Giant Paramagnetism in Small Carbon Coated Copper Nanoparticles

Systematic measurements were performed using XRD, STEM, EPR and PPMS for structural and magnetic properties of different size copper nanoparticles embedded in carbon matrix syntesized by solid phase pyrolysis of polycrystalline copper phthalocyanine (CuPc, Pc= C₃₂N₈H₁₆). Our results on magnetization carried out by vibrational magnetometer in wide range of temperature for average sizes of copper nanoparticles in range of 5-7 nm provide a strong evidence on coexistence of ferromagnetism and giant paramagnetism. At low temperatures we observe a giant paramagnetism, apparently due to the conduction electrons with ballistic mean free path (large orbital magnetism). The values of the specific susceptibility at T= 10K show a record high giant paramagnetism with magnetic specific susceptibility of order ≈1.5×10^-4 emu/gOe while ferromagnetic behavior (M_s ≈ 0.5 emu/g_Cu) with hysteresis was observed from helium up to the room temperature.