Magnetism of stacked multilayered graphene nanostructures in carbon microspheres*

Morphology, structure and magnetic properties of synthesized by pyrolysis (using as precursors metal free phthalocyanine and polyethylene) samples with different concentration of nitrogen in multilayered graphene nanostructures with zigzag edges in carbon microspheres was investigated by XRD, XPS, Raman, HRTEM microscopy, magnetometry, EPR measurements. Studied magnetic characteristics depend on temperature, magnetic field and concentration of nitrogen impurity centers. Prepared sample at Tpyr=700 K demonstrates strong paramagnetism, ferromagnetism and temperature-independent diamagnetism with susceptibility $χ^{Dia}$=-10$^{-6}$ emu/gOe at T=300K. Saturation magnetization vs temperature behavior with maximum magnetization M$_s$ saturation at 20 K closely resembles a spin glass behavior. The itinerant ferromagnetism of π-electrons in narrow impurity bands is interpreted using temperature dependence of spin correlations at zigzag edges in nanographenes. A magnetic hysteresis is also observed under variation of temperature at 100$<$T$<$300 K where magnetization displays diamagnetic character.