Solid-state NMR signals at zero-to-ultra-low-field

Zero-to-ultra-low-field nuclear magnetic resonance (ZULF NMR) is fast emerging as a viable spectroscopic approach to study samples under conditions dominated by internal spin interactions. In the absence of the truncating effects of Zeeman interaction, the NMR signal is determined by J-coupling, dipole-dipole, and/or quadrupolar interactions. But, the low spin-precession frequencies and equilibrium spin polarisation in low external fields necessitate the use of special techniques for detecting the signals. In this article, spin evolution in ultra-low-field regime for various systems is studied and the expected NMR signals are evaluated for solid samples. The methodologies that can be used to make low-field detection feasible especially in case of solid samples are described.