Crossed-coil nuclear magnetic resonance probe for high sensitivity low temperature measurements

A crossed-coil probe suitable for nuclear magnetic measurements at low temperatures is described. The probe may be used with commercial continuous wave spectrometers and enables improved sensitivity to be obtained, particularly at liquid helium temperatures. The electrical balance of the probe is controlled by an external circuit, and because the probe is compact and contains no moving parts, it may be cooled conveniently. Thermal insulation of the sample from the probe is, therefore, unnecessary and high filling factors may be obtained. High performance Dewar vessels may be used giving economy of refrigerant, freedom from microphonic interference, and the possibility of long uninterrupted runs at liquid helium temperatures. Factors that influence the design and performance of probes of this type are discussed.