Cryogenic spin 3/2 nuclear quadrupole resonance: Spin relaxation and electric field gradient via Rabi frequency goniometry

Abstract

A straightforward way to determine the electric field gradient $-$ principal axes frame (EFG-PAF) on single crystal samples with spin 3/2 nuclei is demonstrated. Nuclear quadrupole resonance (NQR) spectroscopy is used to determine the Rabi frequency for ${}^{35}$Cl in a single crystal of potassium chlorate (KClO${}_3$) by comparing the NQR signal for powder and single crystal samples. By exploiting the geometrical dependence of the Rabi frequency with respect to the excitation direction, EFG-PAF is readily determined. Furthermore, relaxation times $T_1$ and $T_2^{\ast }$ were measured at multiple temperatures ranging from $17\text{K}$ to $200$K, extending the results of previous works to colder temperatures where new relaxation mechanisms become dominant. The experiments were performed in a cryogen-free cryostat, which posed distinct challenges compared to a conventional cryogenic cooling setup. The successful operation of the NQR probe within a cryogen-free cryostat has the potential to make the technique more accessible and widen applications.

10 pages, 12 figures

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