NMR of magnetically oriented microcrystals

We review solid-state NMR of magnetically oriented microcrystals. Three-dimensional alignment makes experiments virtually equivalent to single-crystal NMR possible even if the sample of interest is polycrystalline. This leads to characterization of electronic structure through determination of chemical shift and electric-field gradient tensors. The magnetic alignment of microcrystals benefits materials for which it is desirable but difficult to grow a sufficiently large single crystal. Here, we summarize how three-dimensional orientation is achieved through application of a rotating magnetic field with appropriate modulation of amplitude or frequency. We also discuss the condition for alignment, how to experimentally realize spontaneous orientation of individual microcrystals in a common direction, and other expected advantages of this approach. Next, we provide an overview of the current applications of NMR of magnetically oriented microcrystals to ¹³C NMR and ¹⁴N NMR. These applications prove the feasibility of single-crystal NMR even with microcrystalline powder.