Minimizing the Perturbation of the Applied Magnetic Field by Optimizing Solid-State NMR Probe Structures

The NMR probe is likely the most specialized part of the NMR spectrometer with respect to the sample and is often the only component that needs to be exchanged when switching between different NMR samples (<i>e.g.</i> liquid, solids, gels) and experiments (<i>e.g. </i>static, spinning). It is essential that the probe locates the sample in the most homogeneous part of the magnetic field within the magnet, to allow for the best recorded spectra possible. In an ideal case, the probe itself would not perturb the applied magnetic field, yet effects of perturbation can be observed, which is why shimming of the probe is essential before every NMR experiment. In this work we want to present ways to minimize the perturbation of the applied magnetic field by optimizing solid-state NMR probe structures. This is achieved by a combination of simulations and experiments, which take susceptibilities of all parts in the NMR probe into account to then study the net effect upon the sample. Based on those results, modifications to NMR probes can be made, to minimize unwanted contributions. The smaller the perturbation of the applied magnetic field, the narrower the observed possible linewidth and the higher the resolution of the experiment.