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arXiv · 1707.03748

Monovacancy paramagnetism in neutron-irradiated graphite probed by $^{13}$C NMR

Z. T. Zhang·C. Xu·D. Dmytriieva·S. Molatta·J. Wosnitza·Y. T. Wang·M. Helm·Shengqiang Zhou·H. Kühne
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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, $1/T_{1}\propto\exp(-Δ/k_{B}T)$, yielding a singular Zeeman energy of ($0.41\pm0.01$) meV, in excellent agreement with the sole presence of polarized, non-interacting defect moments.

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Z. T. Zhang, C. Xu, D. Dmytriieva, S. Molatta, J. Wosnitza, Y. T. Wang, M. Helm, Shengqiang Zhou, H. Kühne. 2017-12-20. Monovacancy paramagnetism in neutron-irradiated graphite probed by $^{13}$C NMR. https://doi.org/10.1088/1361-648x%2Faa8d47

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