In addition to conventional (high-field) NMR relaxometry studies, NMR relaxometry at (ultra-)low magnetic fields (ULFs) has been recently demonstrated . This became possible due to the application of non-inductive sensors, which are sensitive to low-frequency magnetic signals (particularly in the sub-kilohertz range) . Specifically, atomic magnetometers-offering high near-DC sensitivity, low price, small size, and non-cryogenic operation-have recently been used for such measurements . In ULFs, proton Larmor frequencies are in the range where they overlap with the rate of many slow biochemical processes of interest that occur on the microsecond to millisecond time scale such as protein folding , ligand binding , membrane transport , intramolecular diffusion , oxidation-reduction reactions , and chemical exchange in biomolecules . Therefore, compared to conventional NMR relaxometry, operation at ULFs enables the study of slow processes, as the spin evolution in this field regime occurs at similar timescales. Furthermore, the study of NMR samples in this field regime is especially interesting, as the relaxation properties strongly depend on the magnetic-field strength. This allows for the direct determination of molecular motion parameters .