Sensitivity considerations for NMR in metal single crystals

We report a study of the factors determining the sensitivity of NMR measurements using bulk metal single crystal samples. We show that, in an ideal case, the NMR signal intensity from such a sample can be characterized by a figure of merit which is a function of only the fractional radio-frequency power losses in the coil winding compared to the losses in the sample. This allows the Q factor of the NMR coil to be varied considerably with no appreciable change in the figure of merit, thus permitting the coil Q to be chosen on the basis of the noise characteristics of the spectrometer being used. Measurements indicate that the absolute signal intensity from a metal single crystal with a near-optimum coil is about 1/10 of that from a powdered sample with particle radii approximately equal to the rf skin depth.