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Ferromagnetism in Carbon Based Materials Probed by NMR

We present an investigation of local magnetic fields in ferromagnetic graphite, using nuclear magnetic resonance (NMR) of carbon nuclei. Guided by ab initio calculations, we detect a 13C NMR signal in chemically modified graphite without external magnetic fields, conclusively demonstrating the intrinsic ferromagnetic character of the material. Our work is the first detection of internal fields in carbon-based ferromagnets, and the values of the fields suggest that the magnetism is induced by defects in the material structure.[1] The zero-field NMR signal survives up to temperatures above 200 K, in agreement with previous macroscopic magnetization measurements, providing perspectives for the application of this unique material at room temperature. Furthermore, we investigate the dynamics of domain walls, through measurements of nuclear relaxation times and the ferromagnetic enhancement of the 13C NMR signal. Two dynamically distinct carbon sites are found, and we discuss their origin and the consequences for the microscopic structure of the material.

graphite, ferromagnetism, DFT, NMR

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