The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at 13 C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18-21T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials.
Bibliographical noteFunding Information:
We thank Damir Pajić (from the Laboratory for magnetic measurements at the University of Zagreb) for the SQUID magnetization measurements. JCCF and WLS are grateful to Prof. Tito Bonagamba (from the Physics Institute of São Carlos, University of São Paulo, Brazil) for his help with the development of the computational infrastructure used in this work. The work has been partially supported by Croatian Science Foundation (HRZZ) under the project 2729. The financial support from the agencies FAPES, FAPESP, FINEP, CAPES and CNPq (Brazil) is also gratefully acknowledged.