Design and Development of Key Components for a Low-field Solid-state NMR Magic Angle Spinning (MAS) Probe

High-field solid-state nuclear magnetic resonance (NMR) technology boasts high sensitivity and multi-nucleus detection capability. However, when studying paramagnetic materials like lithium-ion batteries, the strong paramagnetism of transition metal ions (such as Mn3+, Fe3+, etc.) leads to issues like magnetic field inhomogeneity, spectral line broadening, signal attenuation, and inability to perform magic-angle spinning (MAS) at high magnetic fields. Under low-field conditions, the magnetic field distortion induced by paramagnetic effects is significantly reduced, offering a potential solution to these problems. This paper presents a theoretical analysis of the advantages of low-field environments for studying paramagnetic substances. A low-field solid-state MAS probe for a 0.5 T Halbach magnet was developed. Furthermore, a complete low-field solid-state MAS spectrometer was constructed. In experiments, 7Li NMR signals of various paramagnetic samples were acquired at a spinning speed of 12 kHz, verifying the feasibility of the self-developed low-field solid-state MAS technology for paramagnetic samples. This approach addresses the problems of overlapping spin sidebands and MAS failure at high fields, providing a new pathway for NMR research on paramagnetic materials.