Conventional NMR experiments are typically conducted in strong magnetic fields, which serve to polarize the nuclei and induce rapid precession. This strong polarization and fast precession enhance the detected signal, which is recorded inductively by pickup coils.
However, using highly sensitive magnetometers allows for non-inductive detection. In this case, a strong magnetic field is no longer necessary to increase the precession frequency. As a result, detection becomes feasible even in weak—or even zero—magnetic fields.
This is the fundamental concept behind performing NMR spectroscopy in ultra-low fields (ULF). This unconventional approach paves the way for exploring new experimental scenarios. In ULF-NMR and zero-to-ULF regimes, signals from multiple elements can be detected simultaneously. In these conditions, the interaction energy between nuclear spins may become the dominant factor, no longer perturbative compared to the spin-field interaction. Other unique features also characterize NMR spectroscopy in this novel and unexplored regime.