An improved method for low temperature nuclear magnetic resonance (NMR) measurements on metal powders is presented. A Varian Wide-Line NMR Spectrometer of the crossed-coil type is used to observe the resonance in metallic powder samples at liquid nitrogen and liquid helium temperatures. The spectrometer probe, dewar and sample are shown in Figure 1. Powders having particle sizes less than the skin depth are used to permit sufficient penetration of the sample by the radio-frequency magnetic field. Motion of the sample caused by the bubbling refrigerant introduces electromagnetic noise and represents the limiting factor in making accurate measurements. We find that the most satisfactory method for holding the sample stationary in the probe and thereby eliminating this noise is to glue it to the bottom of the dewar with paraffin oil.
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