Nuclear magnetic relaxation dispersion (NMRD) is a versatile tool to study nano-scale dynamic processes, at both fundamental and applied levels. Extremely slow molecular motion on ms to mus timescales and such as protein folding, aqueous complexation and surface adsorption phenomena impact spin relaxation rates strongly in the nT to mT field range. However, this range is inaccessible via conventional NMR systems based on inductive detection at high magnetic fields, since these assemblies are not compatible with magnetic shielding required to reach ultralow fields. Here we demonstrate ultralow-field NMR detection with optically pumped magnetometers and their compatibility with fast-field-cycling apparatus for NMR relaxation measurements between Hz and kHz Larmor frequencies. Beyond simple test experiments to validate performance of the setup, we show applications in mesoporous materials, paramagnetic solutions as well as detection of NMR through thick-walled metal tubes/pipes [1-3]. Detection at ultralow fields eliminates line broadening due to magnetic susceptibility differences, enabling high-resolution J coupling spectroscopy in combination with fast-field-cycling relaxation measurements.
[1] S. Bodenstedt, M. Mitchell, M. C. D. Tayler, Fast-field-cycling, ultralow- field nuclear magnetic relaxation dispersion, arXiv:2012.05546, (2020). [2] M. C. D. Tayler et al., Instrumentation for nuclear magnetic resonance in zero and ultralow magnetic fields, Rev. Sci. Instrum. 88, 091101 (2017) [3] M. C. D. Tayler et al., Ultralow-field nuclear magnetic resonance of liquids confined in ferromagnetic and paramagnetic materials, Appl. Phys. Let. 115, 7 (2019)