Monovacancy paramagnetism in neutron-irradiated graphite probed by¹³C NMR

Abstract

Abstract. We report on the magnetic properties of monovacancy defects in neutron-irradiated graphite, probed by 13 C nuclear magnetic resonance spectroscopy. The bulk paramagnetism of the defect moments is revealed by the temperature dependence of the NMR frequency shift and spectral linewidth, both of which follow a Curie behavior, in agreement with measurements of the macroscopic magnetization. Compared to pristine graphite, the fluctuating hyperfine fields generated by the defect moments lead to an enhancement of the 13 C nuclear spin-lattice relaxation rate 1/T 1 by about two orders of magnitude. With an applied magnetic field of 7.1 T, the temperature dependence of 1/T 1 below about 10 K can well be described by a thermally activated form, 1/T 1 ∝ exp(−∆/k B T ), yielding a singular Zeeman energy of (0.41 ± 0.01) meV, in excellent agreement with the sole presence of polarized, non-interacting defect moments.

Magnetization of Ultraviolet-Reduced Graphene Oxide Flakes in Composites Based on Polystyrene

“…As well known, irradiation with neutrons in graphite can cause numerous defects in it also. Nevertheless, experiments show that only paramagnetism is induced in neutron-irradiated graphite [ 10 , 11 ]. A similar result was obtained upon irradiation with fluorine ions [ 12 ].…”