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Published January 13, 2022 | public
Journal Article

Structure and Magnetism of Few-Layer Nanographene Clusters in Carbon Microspheres

Abstract

The solid-phase pyrolysis method was used to synthesize carbon microspheres, consisting of clusters of few-layer nanographene and amorphous carbon. Powders of metal-free phthalocyanine and polyethylene served as precursors of the synthesized carbon microspheres. The pyrolysis products of metal-free phthalocyanine samples S_(Pc)(700) and S_(Pc)(900) contained 4 and 1 atom % nitrogen, respectively, replacing carbon in the graphene lattice in pyrrolic and pyridinic coordination. There are no impurity nitrogen atoms in the products of the pyrolysis of polyethylene. The S_(Pc)(700) sample showed strong paramagnetism with a concentration of paramagnetic centers of ∼5 × 10¹⁹ spin g⁻¹ and a temperature-independent diamagnetism susceptibility of χ_(Dia) = −1 × 10⁻¹⁶ emu g⁻¹ Oe⁻¹. In a temperature range of 5–300 K, ferromagnetism was also revealed with a temperature dependence similar to that of ferromagnetic cluster spin glasses, with maximum saturation magnetization, M_S^(FM) = 3 × 10⁻² emu g⁻¹, and coercive force, H_c = 400 Oe, at T_(sg) = 25 K. It was shown that the ferromagnetism in the S_(Pc)(700) sample is due to π(p)-electrons of zigzag-type edge states as well as nitrogen impurity atoms. The experimental results are interpreted based on the temperature dependence of the spin correlation length. It was revealed that the temperature dependence of the integral of the magnetic resonance absorption intensity closely resembles the temperature behavior of the saturation magnetization of the ferromagnetic component.

Additional Information

© 2022 American Chemical Society. Received 29 July 2021. Revised 14 December 2021. Published online 4 January 2022. Published in issue 13 January 2022. This work is dedicated to the memory of our colleague Dr. Armen Mirzakhanyan. This work was supported by the RA Science Committee and Russian Foundation for Basic Research (RF) in the frames of the joint research project SCS 20RF-166 and RFBR 20-52-05011 accordingly, as well as by the European Union's Horizon 2020 research and innovation program under grant number 857502 (MaNaCa). The work at California State University has been partially supported by NSF HRD-1547723 and NSF PREM DMR-1523588 grants. The Caltech EPR facility acknowledges support from the NSF (NSF-1531940) and the Dow Next Generation Educator Fund. The authors declare no competing financial interest.

Additional details

Created:
September 15, 2023
Modified:
October 23, 2023